EP3129693A1 - Coupling - Google Patents

Abstract

The invention relates to a coupling between two elongate elements (4,5) with a common central axis (19), wherein a sealing ring (21) deformed under pressure is situated between the end zones of the two elongate elements, and wherein the end surfaces (11,12) are in direct contact with each other under the influence of the pressing means, and wherein the protruding parts (24,25) have on their sides remote from each other rotation-symmetrical first contact surfaces (26,27) which widen in the direction of the end surfaces, and wherein during assembly of the coupling the contact surfaces are urged in axial direction toward each other by urging in radial directions toward each other the parts of a divided pressing ring (29,30) consisting of at least two parts and having a peripheral internal recess with two mutually facing second contact surfaces (31,32) which are substantially complementary to the first contact surfaces and wherein after the end surfaces have been thus pressed against each other a locking means (33) is activated.

Description

COUPLING

The invention relates to a coupling between two elongate tubular or rod-like elements through which medium can optionally flow via respective throughflow spaces, such as tubes, tube stubs, pipes, vessels, bodies, shafts, bars, with a common central axis, wherein

a sealing ring deformed under pressure is situated between the end zones of the two elongate elements, whereby the coupling has become medium-tight as a result of the end zones being moved with some force toward each other during assembly of the coupling;

peripheral laterally protruding parts are added to both end zones;

end surfaces are present on the mutually facing sides of both elongate elements and/or of both protruding parts;

pressing means are present which co-act with the protruding parts brought into at least roughly mutually aligned positions prior to realizing of the coupling and which hold these pressed toward each other while maintaining the deformation of the sealing ring; and

locking means co-acting with the pressing means are present for the purpose of maintaining the relative position of the protruding parts pressed toward each other and thus also maintaining the realized medium -tight coupling between the two elongate elements.

Such a coupling is generally known. Examples are couplings between tubular elements, for instance conduits, tubes, pipes, flexible hoses, segments of jet engines and the like. Such elements are hollow and medium can flow therethrough.

It is possible to envisage a usual generally rotational-symmetrical, so round form. The invention is however not limited thereto. Other external and, in the case of tubes, internal shapes can also be envisaged, for instance oval shapes.

It is also possible to envisage structures through which there is no flow, for instance the coupling between parts of the mast of a wind turbine, the coupling between the rotor and the roots of the turbine blades and the coupling between the nacelle and the underlying rotatable bearing construction supported by the turbine mast and comprising two or more flanges with bearings.

A known coupling is embodied such that the end zones of the two elongate elements have a peripherally arranged flange. The two flanges of the elongate elements are placed opposite each other, a sealing ring is placed between the flat end surfaces of the tubes and the flanges are then urged with force toward each other by a rim of bolts which co-act with nuts and which extend through the through-holes which are present in the flanges and which are placed in register such that a rim of double through-holes results through which the bolts can be arranged. Placing and tightening nuts on the ends of the bolt remote from the bolt heads enables a medium-tight coupling to be realized between the elongate elements. Attention is drawn to the fact that the bolts and the nuts combine two functions, i.e. that of pressing means and that of locking means. A displacement of the protruding parts toward each other with force does after all take place by tightening the nuts with force in a predetennined sequence and repeatedly. Owing to the nature of bolts and screws, in particular the small pitch, there need be no fear of spontaneous loosening of a nut once it has been tightened onto a bolt. The bolts and nuts thus also act as locking means.

The term "prismatic" is understood to mean a structure which has the same cross-section at any axial position. This also includes round or to some extent oval cross-sectional shapes.

The coupling can also be applied between for instance the end zone of a container, such as a vessel or a body closed by a lid, and a tubular element.

It is possible to envisage diameters of several tens of millimetres to substantially larger diameters, for instance in the range of 0.5-6 m.

This known coupling has a number of drawbacks

Because the inner diameter often not correspond to that of the tubular elements, and the positioning of the sealing ring and that of the tubular elements may vary from each other, it is not, or at least not wholly, possible to prevent one or more obstacles, or at least abrupt transitions, occurring in the area of the transition between the inner walls of the tubes. Vortices and turbulence can occur as a result, and it is even often the case that in the case of greater flow speeds such a connection begins to vibrate, hum, whistle or whine, this accompanied by flow losses. It is noted by way of illustration that sound pressure levels often occur in practice in the order of 110-115 dB SPL measured at a distance of 1-2 m and at a more less constant frequency of about 5 kHz. This is a great drawback which is however tolerated in practice.

The nuts of the rim must further be tightened very carefully and in a precisely

predetermined pattern. In the simple case of four bolts and nuts one nut is first slightly tightened, then the diagonally opposite nut and subsequently the remaining third and fourth nut. Through tightening of the second, third and fourth nuts the tension in the first nut will in the meantime have fallen considerably. This must therefore be tightened again. Tightening of the nuts, and thereby realizing of the coupling between the elongate elements, is therefore a precise, protracted task which therefore costs a relatively large amount of time and money. It is also the case that, even when torque wrenches are used, errors or inaccuracies cannot be wholly precluded from the correct realization of such a coupling.

For very high pressures of for instance 50 bar and higher and larger diameters, for instance in the already stated range of 0.5-6 m, it would seem at first sight logical that a relatively large number of bolts are applied. This appears to be a logical choice but has the great drawback that the flanges must be provided for this purpose with the same number of pairs of holes. Holes are mechanically highly undesirable since they weaken the mechanical stiffness and strength of the flanges to very considerable extent. As a result it is necessary, especially for relatively high pressures, to use very thick flanges. For tube couplings with a diameter in the order of a metre and pressures of 50 bar or higher it will further be necessary to expect bolts with a weight of several tens of kilograms. It will be apparent that these are difficult to handle and that the tightening of all nuts with a determined torque in wholly correct manner and in accordance with the set schedule requires much patience, professional skill, concentration and time.

It is further necessary to take into account that at the position of the transition of the tubes, so in the area of the sealing ring, the medium tends to force the tubes apart. This is prevented by the bolts and nuts engaging on the flanges, but there is a distance between the described source of the forces and the zone opposing them, so the area of the nuts and bolts. As a result the flanges are subject to a bending moment force which, especially at high pressures and in the case of tubes and flanges of substantial dimensions, can be very considerable. As a result of the occurring pressure the pressure force on the sealing ring will become smaller due to the force which is present between the tubular elements and which wants to drive the elements apart, which has the consequence that a risk of leakage will even occur because the sealing ring is after all also loaded in radial direction. It will therefore also be necessary to embody a sealing ring such that it can absorb such radial load. It is possible to envisage a reinforcing mat of tensively strong fibres, for instance more or less comparable to the known structure of radial tyres for cars.

When the flanges bend under high pressure in the medium the further undesirable phenomenon occurs that the bolt heads and the nuts are either forced to take up a slightly inclining position, whereby a bending moment occurs in the bolt, or, depending on the dimensioning of the bolt, the bolt remains straight and the bolt heads and the nuts are loaded considerably more heavily in their radially furthest inward zone than on the side remote therefrom. In any event, highly undesirable loads occur which in extreme cases can result in mechanically undesirable phenomena. In addition, the end surfaces tend to move apart under the medium pressure. The pressing force on the sealing ring hereby decreases, this entailing a risk of leakage.

When installing a tube coupling of the prior art type the kink resistance of the coupling depends to a significant extent on the compressibility of the sealing ring. In the case of a relatively hard and mechanically stiff sealing ring the kink resistance will be relatively great, while in the case more rubber-like materials or elastomers are for instance used the kink resistance can leave something to be desired.

A further very significant drawback of the known coupling with flanges provided with through-holes and bolts and nuts is that, owing to the nature of the construction, only discrete relative angular positions of the flanges, and thereby of the elongate elements, are possible. This is the reason why the through-holes always have large dimensions such that it is always possible during assembly of a coupling to still apply a small relative angular displacement. If such an angular displacement is not possible, an elongate element is in practice often then subjected to torsional stress so that the coupling can nevertheless be realized despite the given limitation. At least one elongate element is thus placed structurally under torsional stress, which is

understandably very undesirable, particularly in the light of the very high pressures to be accommodated and temperatures to be withstood.

It is further noted that arranging through-holes in the flanges with a larger diameter weakens these flanges still further. It will be apparent that this is also highly undesirable.

It must further be remembered that the bolts and nuts are situated in the known tube coupling at a substantial distance from the thermal transfer zone in the case where a heated or, conversely, cooled medium is transported through the tubes or in the case of a heat source outside the tube coupling. Substantial temperature differences can hereby occur inside the tube coupling. This could be formulated in that a delayed temperature change always occurs in the area of the bolts in the case of a change in the temperature of the medium in the tubes of the coupling. Such variations in temperature are however very usual in the process industry, for instance cracking plants and the like. Use is after all made of diverse active elements acting on the medium, such as pumps and compressors. There is as a result a very wide spectrum of pressures and temperatures which vary dynamically in an unpredictable sequence. The bolts in particular are subject to fatigue and premature ageing as a result.

Because the known flange coupling is not suitable for any exact calculation other than by making use of empirically determined tables and suchlike information, the known tube couplings are for safety reasons always substantially overdimensioned in practice. This is because it is necessary to take into account that in the case the bolts are for instance heated they will expand and the pressure forces on the seal will be reduced, which may be accompanied by a less reliable seal and even leakage. In the case of for instance a fire in the vicinity of a known tube coupling this may involve a very substantial safety hazard.

Because the bias in the coupling can vary in this way, the screw threads of the bolts and the nuts, when stainless steel is used and particularly in the case of compression fittings, are often silver-plated against scoring. Scoring is the phenomenon of an often strong plastic deformation of the material occurring locally under the influence of excessively high pressures as a result of small contact surfaces. Silver-plating is a costly process but is generally seen as being unavoidable as no safety risks whatever can be taken in for instance the process industry.

With a view to the essential safety standards, these drawbacks of overdimensioning and applying silver coatings and the like are tolerated for lack of any solution to these problems.

As described, the reliability of the seal thus depends to a substantial extent on the dynamic behaviour of the coupling at varying pressures and temperatures.

A coupling of the specified type is further known which is embodied such that the sealing ring is accommodated in a peripheral recess in at least one of the end surfaces; the end surfaces have complementary forms at least over corresponding peripheral zones; the end surfaces are in direct contact with each other at least in said peripheral zones under the influence of the pressing means; and

the scaling ring is embodied such that in the assembled state of the coupling it is deformed elasto-plastically under the influence of the pressing force exerted by the pressing means and has shaped itself in dominant measure to the shape of the peripheral recess(es) while leaving clear some free space.

The end surfaces of the elongate elements, which consist of a mechanically strong and stiff material, for instance stainless steel or the like, in this way lie against each other at least in said peripheral zones and are pressed at least lightly against each other. What is essential is that the force exerted by the pressing means is sufficiently great to ensure that the sealing ring acquires its correct state of deformation during assembly of the coupling and retains it after assembly of the coupling. At the position of the contact of the sealing ring with the wall or walls of the peripheral recess in which it is accommodated it is essential that the sealing ring wholly shapes itself to the associated surfaces during elasto-plastic deformation. These surfaces can never be completely smooth. Microscopic roughness will always remain and the minimum roughness is moreover also determined by the local crystal structure.

The sealing ring lies recessed in the peripheral recess and is therefore substantially not loaded in radial direction. This has the great advantage that, even when medium is fed under high pressure through the tubular elements, the sealing ring is subjected to only limited extent to radial forces. Use can therefore be made for instance of relatively soft rubber types or elastomers, while the leak-tightness of the coupling is nevertheless guaranteed under even the most extreme conditions. It is possible to consider finishing the end surfaces of the tubular elements such that when they co-act they already fulfil a substantial sealing function. Less high mechanical standards for the sealing ring can hereby also be set than in the above described case according to the prior art.

As stated above, the sealing ring has shaped itself in dominant measure to the form of the peripheral recess or recesses while leaving clear some free space in the assembled coupling. This is a condition for ensuring that the end surfaces can press against each other. Noted by way of example is the compression modulus of natural rubber, which is a material which can be envisaged for the sealing ring. Rubber, similarly to for instance water, is a substantially incompressible material. This means that, while it can change shape under mechanical pressure, its volume remains substantially the same. In the present case of for instance a recess with a rectangular radial cross-sectional form and a round rubber ring, so an O-ring, the ring is dimensioned such that its radial cross-sectional area is slightly smaller than the radial cross-sectional area of the recess. The effectiveness of the seal is determined in significant part by the path length per unit of peripheral length, or the surface area, with which the pressure medium is prevented from displacing outward.

Other than is often assumed, it is essential for a good seal that the sealing ring not only displays an clastic but also a local clasto-plastic deformation. This can be understood to mean that, when a sufficient pressure is exerted on the sealing ring, it presses according to the invention against the walls of the cavity enclosing the ring such that both an elastic and a plastic deformation take place. In the area of the pressure contact surfaces the material will be greatly deformed plastically, while mainly elastic deformation occurs in zones surrounding these plastically deformed zones. The plastically deformed zones are thus as it were surrounded in the manner of islands by elastically deformed zones. This is essential under all conditions for a good seal. It must be noted here that, when an assembled coupling must for instance be repaired and has to be dismantled for this purpose, the sealing ring may not be reused but must be replaced by a new sealing ring. In the assembled state of the coupling the material of the sealing ring is locally in a state of hydrostatic pressure, wherein the pressure is equal at every location in the material of the sealing ring.

A coupling of the above specified type is known from US-A-3 746 348.

According to the invention the coupling has the special feature that

the protruding parts have on their sides remote from each other rotation-symmetrical first contact surfaces which widen in the direction of the end surfaces and which have the same shapes but an opposite orientation;

during assembly of the coupling the contact surfaces are urged in axial direction toward each other by urging in radial directions toward each other the parts, with the same radial cross- section at each position, of a divided pressing ring consisting of at least two parts and having a peripheral internal recess with two mutually facing second contact surfaces which are substantially complementary to the first contact surfaces, and the form and inclination of which correspond to those of the first contact surfaces; and

after the end surfaces have been thus pressed against each other a locking means is activated, for instance a locking ring serving as locking means is arranged over the outer surfaces of the pressing ring parts.

Owing to this structure it is possible to wholly dispense with the use of holes, which do after all result in mechanical weakening. Owing to this structure according to the invention a completely smooth and uniform distribution of forces takes place without it being necessary to place bolts and to tighten nuts in accordance with a strict protocol.

In a practical exemplary embodiment the coupling is embodied such that the protruding parts are connected non-mo vably to the associated elongate elements. In this latter case an embodiment is recommended in which the protruding parts are formed integrally with the associated elongate elements or connected non-releasably thereto.

Use can alternatively be made of an embodiment in which the protruding parts are separate of the elongate elements and are coupled thereto by the pressure forces exerted by the pressing means.

The coupling according to the invention preferably has the feature that the or each recess lies symmetrically relative to the central axis.

This avoids any asymmetry, which could after all result in a mechanical load under the influence of the media fed through under pressure which could result in a certain kink at the position of the coupling.

According to yet another aspect of the invention, the coupling has the special feature that the elongate elements are tubular, and the open ends of the two throughflow spaces have the same shapes and the tubular elements are placed in register such that the walls of the two throughflow spaces connect substantially smoothly and evenly to each other.

Any disruption of the medium flow through the coupling is prevented from occurring with this embodiment. The described phenomena of the prior art, such as mechanical vibrations, humming, whistling and whining, are hereby de facto precluded.

In a specific embodiment the coupling has the special feature that

the pressing ring comprises two pressing ring segments which are separated in axial direction and which are each assembled from at least two pressing ring parts;

the locking ring comprises two locking ring parts which are separated in axial direction and which co-act with the two respective pressing ring segments; and

the pressing ring segments are connected to each other by means of an at least more or less conical screw coupling.

Such screw couplings are per se known. Many such screw couplings are however not suitable for the present objective, or hardly so. It must be remembered that a usual conical screw coupling is not self-centering, despite the appearance of correct alignment. Therefore

recommended is a coupling of the above described type which has the feature that

the one pressing ring segment has an external screw thread and another pressing ring segment has an internal screw thread complementary thereto,

the screw threads are superimposed on two for instance truncated conical base surfaces monotonously narrowing and widening respectively in the direction of a central axis,

the longitudinal section of each of the screw threads relative to the central axis is a periodic univalent function which is continuous at least at the inflection points,

the first derivative of the longitudinal section of each screw thread along the base surface is a continuous function; the second derivative of the longitudinal section of each screw thread along the base surface is a continuous function;

the second derivative of the longitudinal section of each screw thread relative to the central axis is a continuous function at least in the region of the inflection points;

the function is calculated on the basis of a Fourier scries; and

the harmonics above a chosen maximum ranking number, for instance 5, are ignored; as a result of which the screw threads are in mutual contact over a substantial surface area differing from line contact.

For extremely high reliability and a total absence of creep the coupling of the above described type can have the feature that the locking ring comprises a monocrystalline material, for instance monocrystalline steel or carbon.

Use can as alternative be made of a variant in which the coupling has a special feature that the locking ring comprises fibres with high tensile strength, for instance of glass, carbon, boron, aramid, reinforced PE (polyethylene).

According to yet another aspect of the invention, the coupling can have the feature that the first and the second contact surfaces both have a truncated cone shape.

In a specific embodiment the coupling has the special feature that the one pressing ring part comprises at least one first permanent magnet, for instance of neodymium; and

the second pressing ring part comprises at least one other permanent magnet co-acting with the first permanent magnet, or a ferromagnetic anchor. Neodymium is an extremely strong permanent-magnetic material. In the case where the ends of the pressing ring parts form the poles of a neodymium magnet and the poles of adjacent pressing ring parts attract each other and the associated surfaces are exactly complementary, in particular extend in radial direction, an extremely strong attachment is realized between the pressing ring parts. It nevertheless remains desirable under all conditions to make use of a locking ring which can for instance prevent the pressing ring falling apart as a result of improper use, in particular impacts.

The pressing ring preferably consists of two parts which can advantageously be identical.

The locking ring can be manufactured from a material which is relatively inherently stiff, such as steel. Use could optionally also be made of a cord, a wire or a tape which is arranged around the pressing ring parts, tightened to a certain tension and subsequently fixed. It is possible to envisage a clamp or a professional industrial embodiment of a known hose clip which comprises a closed tensively strong band, for instance of steel, the periphery of which can be reduced in size by tightening a screw. In relation to the very great forces which occur as a result of the high pressure in the medium in the tubular elements, the force required is essentially negligible. The locking ring need not therefore comply with mechanically very high standards. In a further embodiment the coupling has the special feature that the first and the second contact surfaces are parts of the jacket surfaces of imaginary cones, the half-apex angle of which has a dimension (90-X)°, wherein X has a value such that the pressing ring parts, after being pressed onto the protruding parts, remain in position thereon under the influence of the friction between the contact surfaces, and lies particularly in the following ranges, stated in order of preference, of 55°-85°, 60°-80°, 65°-75°, 67°-73°.

It will be apparent herefrom that a determined preference is evident in the order of magnitude of 70°. What is however essential is that, similarly to the action of a wedge, an axial pressing force occurs due to the radial displacement of the locking ring parts which compresses the sealing ring to the situation in which the end surfaces of the elongate elements press with force against each other.

Very great forces can act on the diverse elements of the coupling. In respect of the inevitable distance between the source of the forces, i.e. the pressure in the medium present in the tubular elements and the contact surfaces, it is not possible to prevent moments of force occurring. These will be substantially lower than those which occur in the prior art flange couplings, although they are not wholly absent. Recommended in this respect is an embodiment in which peripheral rounded recesses which act against notch effect are present in the annular transition areas between the outer surfaces of the elongate elements and the associated truncated conical first contact surfaces.

In another embodiment or in combination with the above described embodiment the coupling can for the same reason have the special feature that peripheral rounded recesses which act against notch effect are present in the annular transition areas between the surface extending between the second contact surfaces and these second contact surfaces of the pressing ring parts.

The coupling can further have the special feature that

the first and the second contact surfaces have smooth rounded forms and have on their wide end zones and on their narrow end zones mutually coinciding tangential cylinders coaxial with the central axis; and

the first and the second contact surfaces have inflection planes with a truncated cone form which have inflection circles in common with the contact surfaces.

Such a coupling has the advantage that there is no need to fear for any notch effect. It is hereby possible to dispense with anti-notch effect provisions in the form of milled recessed rounded grooves. This can have a considerable cost-reducing effect.

Because a technical preference emerges for contact surfaces with shapes largely corresponding to the jacket surfaces of truncated cones, use can advantageously be made of an embodiment in which the contact surfaces have over a substantial area on either side of the inflection circles shapes which at least approximately correspond to the shape of the inflection planes.

The shape of the inflection planes can correspond to the above stated specification, in order of preference, of 55°-85°, 60°-80°, 65°-75°, 67°-73°. With such a dimensioning the Coulomb friction remains decisive for the solidity of the coupling prior to arranging of the locking ring.

In a specific embodiment the coupling has the feature that the axial section of each of the contact surfaces satisfies the equation f(x) = A.sin^B πχ, in which

x = the axial location;

A = a constant directly proportional to the radial dimension of the associated contact surface;

B = a power to be selected, in order of preference: B > 10; B > 20; B > 40. According to a very important aspect of the invention, the coupling has the special feature that the locking ring parts are in engagement with the protruding parts solely through contact between the first and the second contact surfaces. Tt should be appreciated that the end surfaces of the mutually coupled elongate elements must be deemed as the only mechanical hard stop.

Essential to the invention is after all that these surfaces are in pressure contact with each other over at least substantially the whole of their areas. The contact pressure is hereby substantially lower than the contact pressure on the bolt heads and the nuts against the flanges of the known tube coupling while, other than in the known coupling, the extent of compression and deformation of the sealing ring moreover does not depend on the manner in which the coupling is assembled by an engineer, but only on the dimensioning specifications precisely determined in the factory.

Owing to the nature of the coupling according to the invention with the co-acting truncated conical contact surfaces a correct registration of the end zones of the elongate elements takes place of its own accord without any extra effort during assembly of the coupling. This also prevents any irregularity, for instance an obstacle acting as obstacle to flow, occurring at the position of the mutually connecting inner edges of the contact surfaces, also the end edges of the throughflow spaces of the elongate, in this case tubular elements, whereby the above described vibrating, humming whistling or whining may occur during a medium flow. As a result of the described structure with the truncated conical contact surfaces this undesirable phenomenon is substantially wholly prevented.

In order to further ensure a highly accurate registration the coupling can have the special feature that mutually co-acting registering steps connect to the end surfaces.

hi order to have the relative positioning of the end zones of the elongate elements comprising the registering steps take place as easily as possible during assembly of the coupling, the coupling can have the special feature that the registering steps have at least one positioning edge. In a specific embodiment the coupling can have the special feature that the pressing ring parts have a shape widening in radial direction outward and in axial direction to about the radial position of the radial outer edge of the protruding parts such that the local moment stresses in the pressing ring parts are at least more or less constant in the area of the widening form.

The pressing ring parts arc generally U-shapcd in axial section. As a result of this shape in combination with the annular shape the pressing ring parts have a very great bending stiffness. This is caused particularly by the legs of the U. In this respect the intermediate part, which has a generally cylindrical form, need not be mechanically very strong or stiff. It should be apparent however that from a mechanical viewpoint a certain minimum requirement must nevertheless be set therefor in respect of strength and stiffness. In this context the coupling can have the special feature that the elongate elements are tubular and have a determined wall thickness; and the smallest radial dimension of each pressing ring part in the axial area of the largest diameter of the protruding parts is at least approximately as great as the wall thickness of the tubular elements.

Only limited mechanical requirements are set for the locking ring. The local hoop stress on the outer surface of the pressing ring parts is low and the locking ring serves essentially to ensure only that the pressing ring parts co-act with the contact surfaces of the protruding parts such that the end surfaces of the elongate elements remain lying against each other under all conditions.

The coupling can in this respect have the feature that the locking ring fits tightly around the assembled pressing ring, optionally with some deformation.

In an important embodiment the coupling has the special feature that the locking ring is manufactured by stretching a ring of a steel to the desired circumference while strengthening the material such that the obtained locking ring consists of spring steel with a tensile strength that is increased substantially relative to the original steel.

In this embodiment the spring steel, which takes the form of a metal band, can have a small thickness as a result of its very high tensile strength. It is for instance possible to envisage a thickness in the order of only 0.5 mm.

The starting material, for instance chrome-nickel steel with a tensile strength in the order of 200 N/mm², can in this way be transformed into spring steel which through strengthening has acquired a tensile strength of for instance 1000 N/mm² or more.

For easy assembly of the coupling the coupling can have the feature that

the assembled pressing ring has a prismatic outer surface and the locking ring has a correspondingly formed prismatic locking ring part;

a peripheral positioning edge connects to the prismatic locking ring part on at least one axial end; and the prismatic part of the locking ring is brought into its position by passing over the positioning edge and the locking ring being pushed on further in sliding manner, optionally with some force.

The term "prismatic" is understood to mean a structure which has the same cross-sectional form at any axial location. This cross-section can for instance be round, elliptical or polygonal.

Use can be made of a simple tool which engages on the one side on at least one elongate element and on the other co-acts in pushing manner with the associated end edge of the locking ring.

According to a determined aspect of the invention, the coupling has the special feature that the outer surface has a cylindrical form. Such a rotation-symmetrical form is technically logical and is along the same lines as those embodiments of the present coupling in which the elongate elements can be coupled at any desired relative angular position.

The coupling can alternatively have the special feature that the outer surface has a non- round form.

This coupling can for instance be embodied such that the outer surface has a cross-section with the form of a regular polygon, in particular a hexagon or an octagon. Such an embodiment has the practical advantage that the pressing ring parts can be pressed toward each other more easily and with a lower contact pressure with a tool for the purpose of realizing the coupling than in the case of an outer surface of a cylindrical form. Especially in the case where use is made of a conical screw connection, the pressing ring parts must be pressed against each other and subsequently rotated with force. It will be apparent that a tool engages more easily on a non-round structure, for instance a polygonal form, than on a round structure.

According to yet another aspect of the invention, the coupling has the special feature that the locking ring is crimped onto the pressing ring either by first being heated, subsequently being slid into position over the pressing ring and finally being allowed to cool, or by first cooling the pressing ring, for instance using liquid nitrogen, subsequently sliding the locking ring into position over the pressing ring and then heating the pressing ring. Such a coupling has the advantage of being relatively easy to realize, i.e. by heating the pressing ring with a heating device or by cooling the pressing ring parts such that the locking ring can be pushed with little or no force over the pressing ring parts and is subsequently secured thereon under tensile stress by equalizing of the temperature of the pressing ring parts and the locking ring. For removal purposes the locking ring can be pushed off the pressing ring parts with a tool or for instance cut through and replaced by a new locking ring before reassembly of the coupling.

An essential advantage of the embodiment of the coupling according to the invention with the co-acting truncated conical contact surfaces is that, other than the prior art tube coupling with flanges, bolts and nuts, it can not only be assembled in discrete relative positions of the elongate elements but the relative angular position of the tubes can be chosen as desired without any limitation. Even some rotation of the end zones of the elongate elements can if desired take place during assembly should conditions make this desirable. Other than as described above in the case of the prior art, such a rotation does not have the consequence that torsional forces occur in the elongate elements. The elongate elements in the coupling according to this aspect of the invention, with all partial aspects, remain wholly free of any torsional stress under all conditions. This must be deemed a very essential advantage of this aspect of the invention.

For determined applications it may be required for the elongate elements to be locked against a relative rotation. Stated by way of example is a hollow drill shank for exploring ground layers when searching for gas or oil. For such an application the coupling can have the special feature that the two protruding parts are locked by rotation locking means against relative rotation around their common central axis.

A highly practical embodiment has the special feature that the rotation locking means comprise a key coupling between the two protruding parts and at least one pressing ring part.

As described above, it is essential that the contact surfaces press against each other in the assembled coupling. Recommended in this respect is a coupling which has the feature that the peripheral recess has a form relative to the sealing ring such that pinching of the sealing ring between the end surfaces is precluded during assembly of the coupling.

This coupling can for instance be embodied such that the sealing ring has a round cross- sectional form, the diameter of which is only a little larger than the radial width of the recess such that, prior to assembly of the coupling, the sealing ring can be pressed with some elastic deformation into the recess and the axial depth of the recess is greater than the cross-sectional radius of the sealing ring.

The material of the sealing ring can be of any suitable type. The coupling can for instance have the special feature that the material of the sealing ring is a natural rubber, a synthetic rubber, a rubber-like material or an elastomer. It is possible to envisage a rubber or a rubber-like material with a hardness in the order of magnitude of 60-70 Sh(A).

In an embodiment in which for instance the pressures or temperatures can be extremely high, an embodiment can be envisaged in which the material of the sealing ring or an optional cover layer thereof is a metal which has a lesser hardness and/or a lower yield point than the material of at least the walls of the peripheral recess.

An embodiment can also be envisaged in which the sealing ring comprises a crystalline material with a cover layer of a rubber-like material or an elastomer, such as PTFE, or copper, silver or babbitt. Pinching of the sealing ring between the end surfaces during assembly of the coupling can also be prevented effectively with an embodiment in which both side walls of the or each recess connect via an outward widening surface to the associated end surface.

According to another aspect of the invention, the coupling according to the invention has the special feature that the end surfaces arc flat and extend perpendicularly of the axial direction. Flat surfaces have the advantage that they can be manufactured mechanically in a relatively simple manner and can be ground with a very high dimensional accuracy and low roughness. Even casting and forging can be performed with a high degree of accuracy and a low surface roughness using modern techniques. For understandable reasons it is practical in general to ensure that the end surfaces extend perpendicularly of the axial direction. The total freedom in the relative angular position of the elongate elements of the coupling is after all not hereby restricted under any circumstances whatever.

The same consideration applies for a variant in which

the end surfaces have a profile pattern which is wave-shaped, in particular sine-shaped relative to a main plane extending at least more or less transversely of the axial direction; and the or each peripheral recess is located in a peripheral zone free of profiling.

It must be assumed here that the flat main planes on which the profiling is superimposed also extend perpendicularly of the axial direction. This choice can also have the advantage in some conditions that the two elongate elements which together form part of the coupling can be identical. This is not essential. The only requirement with which the coupling must comply is after all that the relevant main planes, whatever form they have, are complementary. For the freedom of the relative rotation both main planes must, in addition to being complementary, also be relatively rotatable around the central axis. It is for instance necessary in the case of truncated conical end surfaces with a peripheral sine-shaped profiling superimposed thereon to make sure that no undercuts occur in the general shape obtained with this superimposed form.

According to yet another aspect of the invention, the coupling has the feature that the sealing ring is hollow and consists of a material, for instance metal, which is inherently stiff and tensively strong relative to rubber, optionally with a relatively deformable cover layer or a cover layer of a material with a lower yield point than the material of the sealing ring.

Metal sealing rings have the advantage of generally having a higher temperature resistance than rubber-like materials, elastomers and the like. They can however have the drawback under some conditions that they are less well able to withstand chemically aggressive media. Use can therefore be made of a relatively resilient cover layer, for instance of a chemically substantially wholly inert material such as PTFE.

According to yet another aspect of the invention, the coupling has the special feature that the elongate elements are tubular and the wall of the sealing ring has on its side facing toward the throughflow space at least one continuous pressure-equalizing hole in the area of the associated end surface. The medium pressure is hereby transmitted via the generally very small gaps between the end surfaces to the cavity inside the sealing ring. This latter hereby expands, which can result in a substantial contribution toward an excellent seal.

This latter variant can be embodied such that the wall of the scaling ring has a rim of pressure-equalizing holes.

In yet another embodiment the coupling has the special feature that the wall of the sealing ring has a slotted hole extending over the whole periphery of the sealing ring.

The coupling according to the invention with a hollow sealing ring can have the special feature that the material of a sealing ring consisting of one material or the materials of a sealing ring of laminated construction is/are respectively chosen from the group including: steel, spring steel, Inconel, silver, copper, titanium and alloys on the basis of these materials, such as beryllium copper. A laminated construction of the sealing ring can for instance be realized by rolling or explosive deformation followed by a modelling process with which the ring is brought into the desired form, for instance using, among others, a laser-welding process.

According to yet another aspect of the invention, the coupling can be embodied such that the elongate elements are tubular and a tubular element connecting thereto is connected medium- tightly to the free end of at least one of the tubular elements, for instance is welded thereto. A compression fitting can also be applied for the connection instead of a welded connection.

This latter variant can advantageously have the special feature that the two elongate elements are tubular and have throughflow spaces of the same cross-sectional form, are provided with complementary peripheral registering steps prior to being welded to each other, are slid into each other and subsequently welded to each other over an external orbital weld zone such that the walls of the mutually connecting throughflow spaces connect substantially smoothly and evenly to each other. As in the above described embodiment with registering steps in the area of the widened portions and the end surfaces, this embodiment achieves that the flow can take place without any obstacle and without undesirable side-effects such as vortices, turbulence, vibration, humming, whistling and whining.

This latter embodiment can advantageously have the special feature that the peripheral end edges of the two tubular elements are chamfered such that they together bound a generally V- shaped peripheral groove which is filled with weld material following the welding operation. After the V-shaped peripheral groove has been filled with weld material, the excess weld material can if desired be removed by a grinding operation such that the outer surfaces of the two tubular elements also connect substantially smoothly and evenly to each other.

In yet another embodiment the coupling can have the special feature that a compression fitting is connected to the free end zone of at least one tubular element for the purpose of connection to a further tubular element or a flexible conduit or hose. A coupling between different tubular elements can hereby be realized quickly and easily. It should be understood that the advantage of a compression fitting is that during assembly some axial displacement of the tubular elements to be coupled to each other can if necessary still be allowed. This can be a practical consideration in some circumstances. A welding operation for welding further tubular elements to the tubular elements of the coupling could also be dispensed with in some circumstances.

In a further embodiment the coupling has the feature that

the elongate elements are tubular;

a flexible conduit or hose connects directly to at least one tubular element of the coupling; the conduit or hose is pushed over the outward protruding part of the tubular element as far as a stop surface forming part of the end zone of the associated tubular element; and

the edges of the pressing ring parts located radially furthest inward press the flexible conduit or hose with force sealingly against the outer surface of the end zone of the associated tubular element.

Of great importance is that, at variance with the above described prior art coupling with flanges, bolts and nuts, the coupling according to the invention lends itself to an exact analysis and calculation for the purpose of optimizing the design on the basis of set design requirements. The invention provides in this respect a coupling of the type according to the invention in which the coupling is designed on the basis of an exact analysis, for instance with a computer and the use of software for performing an iterative, highly non-linear finite element calculation in which the friction forces between the contact surfaces are taken into account.

According to yet another aspect of the invention, the coupling according to the invention can have a special feature that

the elongate elements are tubular;

a sleeve serving as sealing ring extends over the end zones of the tubular elements;

the sleeve lies tightly over the outer surfaces of the end zones of the tubular elements; the two side zones of the sleeves on either side of the central zone thereof narrow toward their free ends;

the sleeve is accommodated in the peripheral recesses in the end surfaces of the protruding parts;

the recesses are the same as each other;

the central zone of the sleeve has a peripheral inner flange which extends from its inner surface and which extends over at least a part of the wall thickness of the tubular elements between the end surfaces of these elements and is in pressure contact with a least a part of the end surfaces of the tubular elements; and the end surfaces of the separate protruding parts are urged toward each other under the influence of the pressing means such that the axial displacement of the protruding parts in a direction toward each other during assembly of the coupling defonns the side zones of the sleeve radially inward, whereby the tubular elements also deform inward locally, which defomiations are retained under the influence of the pressing means and the locking means following the assembly of the coupling;

this such that the two tubular elements are coupled sealingly to each other while using the sleeve by two compression fittings which are the same and are placed symmetrically relative to the end surfaces of the tubular elements.

In a first practical embodiment of this latter aspect the coupling can be embodied such that the inner flange extends over the whole wall thickness of the tubular elements. It must be taken into account here that, on the basis of rheological considerations, it is recommended that the inner surfaces of the tubular elements connect to each other without any appreciable abrupt transition. When an inner flange of the latter stated type is used, it must therefore be manufactured with a certain degree of accuracy in order to satisfy this criterion.

This latter embodiment can advantageously be embodied such that the end surfaces of the tubular elements are flat.

The coupling can alternatively be embodied such that the inner flange extends over a part of the wall thickness of the tubular elements and the end surfaces of the tubular elements are in contact with each other over the remaining part of the wall thickness.

In yet another embodiment the coupling can be embodied such that the end surfaces of the tubular elements together bound a generally V-shaped groove. The V-shaped groove can in principle have any depth, for instance from 0.3x the wall thickness to Ix the wall thickness. It is essential under all conditions that the inner flange provides for an accurate symmetrical positioning of the side zones of the sleeve over the end zones of the tubular elements.

According to yet another aspect of the invention, the coupling has a special feature that the central zone of the sleeve has a peripheral outer flange which extends from its outer surface and which is accommodated fittingly in an annular cavity which is bounded by two peripheral registering steps which are the same and which connect to the peripheral recesses; such that the outer flange ensures a symmetrical positioning of the protruding parts relative to the end surfaces of the tubular elements during the assembly of the coupling.

Both a pressure coupling and a compression fitting according to the invention can be realized with a specific embodiment, in which

the first and the second contact surfaces are parts of jacket surfaces of imaginary cones on which complementary co-acting screw threads are superimposed; the projections in axial direction of the two pairs of complementary screw threads coincide with each other or are rotated through a certain angle relative to each other;

the half-apex angle of the cones has a dimension (90-X)°, wherein X lies in the following ranges, stated in order of preference, of: 35°-55°, 40°-50°, 43°-47°;

rotation locking means arc present in order to block the relative rotation of the protruding parts during and after assembly of the coupling; and

the pressing ring parts are pressed toward each other and rotated together with force by means of a tool during assembly of the coupling such that, as a result of the co-action of the conical screw threads, the end surfaces are brought into and, after assembly, held in contact with each other at least in the peripheral zones.

Reference is made for the at least more or less conical screw threads to the European patent EP-B-2 268 930. This patent shows that, with the screw connection protected by this patent, even with relatively small angles of rotation, for instance in the order of 0.2x-0.7x a revolution, the screw connection can already have reached its stable end position, other than is the case with usual screws which require several complete rotations in order to reach this position.

A usual conical screw thread has the drawback of not being self-centering. This is the case however with the screw connection according to EP-B-2 268 930. Because the screw threads of this patented screw thread are in mutual engagement over relatively large contact surface areas, the pressure at the position of the contact zones is relatively small as a consequence of the large contact surface area, whereby only elastic and not plastic deformation takes place. As a result such couplings according to this patent can be repeatedly realized and uncoupled again in practically unlimited manner. Scoring, i.e. the plastic deformation, does not occur owing to the low contact pressure. Attention is drawn in this respect to the fact that the generally known couplings, for instance hose couplings and the like of Gardena/Husqvarna (trade names), suffer premature wear and ageing as a result of the very high contact pressures which occur.

The pairs of complementary screw threads on the pressing surfaces of the two protruding parts must be exact projections of each other in axial direction. It is therefore of essential importance that the rotation locking means are always placed in correct manner by an engineer during assembly of the coupling. Important in this respect is an embodiment in which the rotation locking means are embodied such that they enable only one relative angular position of the protruding parts. It is possible here to envisage for instance the use of two or more locking pins on the one end surface which are disposed such that they can engage in only one way in

corresponding blind holes in the opposite end surface.

The compression fittings of the type according to the invention can be assembled and taken apart again very easily. With a correct dimensioning and inter alia the use of conical screw connections of the type according to the European patent EP-B-2 268 930, there need be no fear of scoring and other undesirable irreparable damage. Compression fittings from, among others, the firms Gyro and Swagelock (trade names) are highly susceptible to this phenomenon. Such compression fittings can therefore be realized only once in practice and must be completely replaced after dismantling.

The tube coupling according to the invention can also be applied with great advantage to the mutual coupling of the tubular segments of jet engines. The usual jet engines of for instance General Electric, or GE, Rolls-Royce, or RR, and Pratt and Whitney (trade names) have the very great drawback that the many segments of the housing and the segments of the gas turbine accommodated therein are coupled to each other with rims of bolts and nuts as according to the above described prior art. Because as will be apparent extremely high standards are set for jet engines for safety reasons and the number of bolts and nuts to be arranged lies in the order of many- thousands per jet engine, it will be evident that application of the tube coupling according to the invention will also provide very great technical, safety engineering and economic advantages in the case of jet engines. The human factor, which is so decisive in realizing the prior art tube couplings with flanges, bolts and nuts, is in fact wholly precluded with the invention. With the tube coupling of the above described type with at least to some extent truncated conical co-acting contact surfaces the engineer need after all only ensure that, when a radial pressure is exerted on the pressing ring parts, they urge the protruding parts, and so the end surfaces, simultaneously toward each other. The described position is obtained with this simple operation. This position is fixed with a locking ring around the pressing ring parts. This coupling according to the invention is therefore foolproof. Added to this is the fact that it can be assembled in a fraction of the time needed to arrange a large number of bolts and nuts, this resulting in a substantial economic advantage.

In yet another embodiment the coupling has the special feature that registered peripheral recesses are present in both end surfaces, in each of which recesses a sealing ring is

accommodated, which registered sealing rings co-act sealingly with each other. This can achieve that both coupling parts can be given a completely symmetrical, even identical form, which can offer advantages in some circumstances. In an important embodiment the coupling has the special feature that the pressing ring parts are connected on the one side by an axial hinge and on the other side comprise respectively a resilient locking tongue with a first hook part and a locking protrusion means with a second hook part co-acting therewith. With this embodiment it is possible to dispense with the use of a locking ring for locking the coupling in its operational state. Exerting a sufficient more or less radially inward directed force ensures that the end surfaces come into contact with each other. The co-acting hook parts fix the coupling in this position.

In a further development this variant can have the special feature that the locking protrusion means comprise a number of at least more or less tangentially disposed second hook parts. The array of second hook parts form a ratchet, whereby the greatest possible pressing force can always be realized and there is no need to fear that the coupling will spring open during assembly because of an incorrect manoeuvre.

hi yet another embodiment the above described hinge connection is omitted. Such a coupling has the feature that both pressing ring parts comprise a resilient locking tongue with a first hook part and a locking protrusion means with a second hook part, which first hook parts co- act in locking manner with the second hook parts of the other pressing ring part. It will be apparent that this embodiment can also be embodied such that use is made of an array of at least more or less tangentially disposed second hook parts. Also important in this embodiment is that it is possible to opt for an embodiment in which both pressing ring parts are identical.

In an embodiment in which the coupling comprises pressing ring parts in which the closure and the maintaining of the closing force between the pressing ring parts is at least partially provided by magnet means, for instance two co-acting permanent magnets or a permanent magnets co-acting with a ferromagnetic anchor, the coupling can advantageously have the feature that at least one pressing ring part comprises two permanent magnets or a generally U-shaped permanent magnet, the poles of which debouch at the separating surface between the pressing ring parts; and a ferromagnetic shunt movable from outside by operating means is present which is movable between a passive position, in which it extends at a distance from the poles and so substantially does not influence the magnetic field between the poles; and an active position in which it extends between the poles and reduces the strength of the magnetic field substantially to zero.

Such an embodiment has the great advantage that the closure with magnet means can be very strong and reliable, and can moreover be easily deactivated.

The coupling can in similar manner have the special feature that at the separating surface between the pressing ring parts a first pair of magnetic poles debouches at the one pressing ring part and a second pair of magnetic poles debouches at the other pressing ring part; and at least one of the pairs is movable from outside by operating means between a first position, in which the pairs attract each other; and a second position in which the pairs are substantially free of mutual attraction.

This latter variant can with great advantage be embodied such that the at least one pair can be moved by the operating means between the first position, the second position; and a third position in which the pairs repel each other.

It should be understood that the first position is the coupled position in which the coupling is active, the second position is a neutral position in which the attractive magnetic forces have been reduced to substantially zero, and the third position in which the pairs repel each other and so contribute toward an easy dismantling of the coupling. It should be understood that both the attractive and the repelling forces between respectively opposite and like magnetic poles can be very high in the case of a small mutual distance between the end surfaces of these poles. The displacement between the first and the second or the first, the second and third position must therefore take place such that the magnets are not pulled away from each other transversely of the plane of the poles, since this attractive force is after all very high there, but must be displaced laterally in this plane. The displacement between said positions must therefore preferably take place in transverse direction relative to the magnetic field between the poles.

In order to be able to overcome the attractive magnetic forces of an active coupling use can be made of mechanical means for exerting on the two pressing ring parts in the area of the at least one permanent magnet a separating force urging these pressing ring parts apart.

In the simplest case use could be made of a screwdriver which by means of rotation can exert opposing forces on the two pressing ring parts in the area of the separating surface, for instance via recesses arranged for this purpose on the outer surface in the pressing ring parts.

According to yet another aspect of the invention, this latter embodiment can be embodied such that the mechanical means are also configured to serve as ferromagnetic shunt.

Use is made in this embodiment of a more or less screwdriver-like auxiliary means, at least the active front side of which is ferromagnetic and which by means of a modified shaping of the pressing ring parts forms a ferromagnetic shunt between the magnetic poles when inserted into respective recesses, whereby the effective magnetic attractive force between the two pressing ring parts is reduced very substantially, and moves the pressing ring parts apart with for instance a rotation in the manner of a screwdriver.

Very simple is an embodiment in which the mechanical means are embodied unitarily with the operating means.

The invention will now be elucidated with reference to the accompanying drawings.

In the drawings:

figure 1 shows an axial section through a coupling between two prior art tubular elements; figure 2 shows a section corresponding to figure 1 in which the deformations occurring in the case of load by a medium under pressure are shown in highly exaggerated manner;

figure 3 is a perspective view of the tube coupling according to figure 1 ;

figure 4 shows an axial section corresponding to figure 1 through a first embodiment of a tube coupling according to the invention comprising a flange connection with bolts and nuts and a countersunk sealing ring according to the invention;

figure 5 shows the detail V according to figure 4 on larger scale;

figure 6 shows a variant according to figure 5 with a peripheral registering step;

figure 7 shows an axial section of an embodiment of the tube coupling according to the invention in which the widened portions on the end zones of the associated tubular elements are provided with truncated conical contact surfaces which co-act in pressing manner with the correspondingly formed contact surfaces of a pressing ring consisting of parts, which parts are held together by a locking ring;

figure 8 shows an axial section corresponding to figure 7 in which the pressing means comprise two conical screw threads;

figure 9 is an exploded view of the tube coupling according to figure 8 in which the diverse components are placed at mutual distance such as prior to the assembly of the tube coupling;

figure 10 shows an axial section corresponding to figure 8 in which the pressing means comprise inclining pressing surfaces having the general shape of f(x) = sin²⁰7ix;

figure 11 is an exploded view of the tube coupling according to figure 10 in which the diverse components are placed at mutual distance such as prior to the assembly of the tube coupling;

figure 12 shows an axial section corresponding to figures 8 and 10 in which the pressing means comprise two at least more or less conical screw threads, wherein the axial section through the base plane satisfies the equation f(x) = sin²⁰jix;

figure 13 is an exploded view of the tube coupling according to figure 12 in which the diverse components are placed at mutual distance such as prior to the assembly of the tube coupling;

figure 14 shows an axial section corresponding to figure 1 of a tube coupling according to the invention on the same scale as figure 1;

figure 15 shows an assembled tube coupling according to the invention corresponding to figure 3 and drawn on the same scale as figure 3;

figure 16A shows a view corresponding to figure 7 of an embodiment in which a peripheral registering step connects to the end surfaces;

figures 16B, 16C and 16D show variants with positioning edges on the registering steps in accordance with the detail XVI of figure 16 A;

figure 17 is an exploded view of the embodiment of figure 14;

figure 18 is a partially broken-away exploded view corresponding to figure 17 of a variant in which the widened portions have keyways and one of the pressing ring parts has an integrally formed key such that the tubes can be placed in only one relative angular position and are locked against rotation in this position;

figure 19 is a partially transparent perspective view of a coupling during assembly thereof making use of a tool;

figure 20 shows an axial section corresponding to figure 14 through a coupling according to the invention during assembly thereof as according to figure 19; figure 21 shows an axial section corresponding to figure 20 during dismantling of the coupling making use of the tool according to figures 19 and 20;

figure 22 shows on enlarged scale an axial section corresponding to the detail XXII of figure 16D through the widened portions at the position of the end surfaces, with a rectangular recess in which a substantially undeformed O-ring is placed as scaling ring prior to assembly of the coupling;

figure 23 shows on enlarged scale a detail corresponding to the detail XXIII of figure 16A of the situation in which the coupling is assembled and the O-ring is compressed in the recess while leaving some space clear;

figure 24 shows a section corresponding to figure 22 through an embodiment of an impractical embodiment by way of elucidating the risk of pinching of material of the sealing ring during placing of the end surfaces against each other during assembly of the coupling;

figure 25 shows a view according to figure 24 of an embodiment in which the risk of pinching is practically precluded by chamfering the edges of the recesses;

figure 26 shows a section as according to figures 24 and 21 of an embodiment in which the depth of the recess has a value lying between 0.5x and lx the diameter of the cross-section of the sealing ring;

figure 27 show s an axial section through a variant of the embodiment according to figure 7 in which rotation-symmetrical, at least more or less sine-shaped profiles are superimposed on the flat end surfaces on either side of the locking ring recess, which profiles of both end surfaces are complementary in the non-assembled state of the coupling;

figure 28 is a perspective view of the coupling according to figure 27;

figure 29 shows a section corresponding to figures 16B, 16C and 16D through an embodiment in which the sealing ring is hollow and consists of metal with a cover layer and has a pressure-equalizing slotted hole extending over the whole periphery of the sealing ring;

figure 30A shows a section corresponding to figure 29 through a sealing ring provided with a rim of pressure-equalizing holes;

figure 30B is a perspective view of a part of the sealing ring according to figure 30A; figure 31 shows an axial section through a tool for fixing the registered positions of a tube stub of a coupling according to the invention and an external tube for welding thereof to each other;

figure 32 shows a cross-section through the tool and the tubes according to figure 31; figure 33 shows a variant of the welded connection sought as according to figures 31 and 32 in which the tube stub of the pipe connection according to the invention and the additional tube have complementary peripheral registering steps as well as respective chamfered surfaces with the form of truncated cones which together define a V-groove for the purpose of the welded connection;

figure 34 shows a coupling according to the invention comprising a tube coupling according to figure 7 and compression fittings connecting on either side thereto;

figure 35 A shows a variant of the tube coupling according to figure 16A in which a flexible hose is connected to one end by means of a clamp coupling;

figure 35B shows a part of the variant according to figure 35A on larger scale;

figure 36 shows an axial section corresponding to figure 35A through a tube coupling in which a flexible hose is connected to both ends by means of a clamp coupling;

figure 37 shows an axial section through a hose coupling which is commercially available from the manufacturers Gardena/Husqvarna (trade names);

figure 38 is an exploded view of the known coupling of Gardena/Husqvarna (trade names); figure 39 is an exploded view of a coupling which is a variant of the coupling according to figure 36 on the same scale as the known coupling according to figure 38;

figure 40 is an axial section corresponding to figures 35A, 35B and 36 in which the pressing ring parts are connected to each other by a conical screw connection;

figure 41 is an axial section through a variant of the embodiment according to figure 40; figure 42 shows a further variant of the coupling according to figure 40;

figure 43 shows an axial section through a first embodiment of an alternative tube coupling according to the invention which is based on the use of two compression fittings;

figure 44 shows in one graph schematic representations of the tension curves of steel, aluminium and softer metals such as copper and silver;

figure 45 shows an axial section corresponding to figure 43 through a second embodiment of a tube coupling according to the invention which is based on two compression fittings;

figure 46 shows the detail XLI of figure 45;

figure 47 shows a view corresponding to figure 46 of a variant;

figure 48 shows a view corresponding to figures 46 and 47 of a further variant;

figure 49 is a cut-away schematic perspective view of a known jet engine which incorporates a large number of prior art flange couplings;

figure 50 is a perspective view of a part of the housing of a jet engine, two segments of which are being coupled to each other by an engineer in the manner according to prior art using flanges and bolt/nut connections;

figure 51 shows a flange section in axial direction of a tube connection on the basis of flanges, bolts and nuts forming part of the jet engine according to figure 49; figure 52 shows on the same scale an axial section corresponding to figure 1 through a tube connection according to the invention for replacing the tube connection according to figure

51;

figure 53 shows an axial section through a variant of the tube coupling according to figure 43 in which the pressing means comprise two conical screw threads;

figure 54 shows an axial section corresponding to figure 45 through a variant of the tube coupling according to the invention in which the pressing means comprise two conical screw threads;

figure 55 is a partially transparent perspective view corresponding to figure 19 of the variant of the tube coupling according to figures 8, 9, 53 and 54 during assembly thereof while making use of a tool;

figure 56 show s an axial section of the tube coupling according to figure 39 on the same scale as figure 37;

figure 57 shows a section corresponding to figures 24, 25, 26 in which both peripheral protruding parts are provided with identical recesses in which identical sealing rings are accommodated;

figure 58 is a perspective view corresponding to figure 39 in which both hoses have been arranged on the coupling pieces;

figure 59 shows a cross-section through the coupling according to figure 58;

figure 60 is a perspective view of an opened pressing ring in which the hinge is not a film hinge as in figure 8 but is embodied as a divisible hinge with a separate pin;

figure 61 shows a cross-section through the pressing ring according to figure 60;

figure 62 is a perspective view of a pressing ring partially corresponding to the pressing ring according to figure 39 but provided with a closing tongue with a number of teeth embodied as ratchet;

figure 63 shows a cross-section through the pressing ring according to figure 62;

figure 64 is a perspective view of a pressing ring which consists of two separate identical pressing ring parts in accordance with the upper pressing ring part in the embodiment according to figure 62;

figure 65 shows a cross-section of the pressing ring according to figure 64;

figure 66 is a perspective view of an opened pressing ring with a peripheral recess in which a strap can be placed in countersunk manner, the strap being either integrally formed on the pressing ring parts or being a separate strap;

figure 67 shows a section through the pressing ring according to figure 66;

figure 68 is a perspective view of an opened pressing ring, the pressing ring parts of which are provided with respectively hook tape and loop tape; figure 69 shows a cross-section of the pressing ring according to figure 68;

figure 70 is a perspective view of a pivotable pressing ring in which the pressing ring parts are provided with mutually attracting magnet poles;

figure 71 shows a cross-section through the pressing ring according to figure 70;

figure 72 is a perspective view corresponding to figure 70 of an embodiment in which by means of a ferromagnetic implement the magnet means can be short-circuited and the pressing ring can be opened by a turning movement;

figure 73 shows a cross-section through the pressing ring according to figure 72;

figure 74 is a perspective view of a pressing ring with permanent magnets and a shunt which can be activated and deactivated and which can also serve as mechanical auxiliary means for opening the pressing ring;

figure 75 is a front view of the pressing ring according to figure 74;

figure 76 shows the cross-section of the pressing ring according to figure 74;

figure 77 is a perspective view of a pressing ring in a subsequent embodiment;

figure 78 shows a horizontal section through the pressing ring according to figure 77; figure 79 is a partially transparent front view of the pressing ring according to figure 77; figure 80 shows a vertical section through the pressing ring according to figure 77;

figure 81 is a perspective view of yet another embodiment of a pressing ring according to the invention;

figure 82 shows a horizontal section through the pressing ring according to figure 81; figure 83 is a partially transparent front view of the pressing ring according to figure 81 ; figure 84 shows a vertical section through the pressing ring according to figure 81;

figure 85 shows a cross-section of a permanent magnet embedded in an undercut cavity in a plastic component by injection moulding;

figure 86 is a bottom view of the component according to figure 85 with permanent magnet;

figure 87 shows a cross-section of an alternative in which the magnet likewise has an undercut form and is anchored in the plastic;

figure 88 is a bottom view corresponding to figure 86 of the pressing ring part according to figure 87;

figure 89 shows a cross-section of an alternative wherein the magnet is received not in an undercut cavity but in a prismatic cavity, i.e. a cavity having the same cross-section at any axial position, the magnet being generally star-shaped;

figure 90 is a bottom view of the pressing ring part according to figure 89 showing the star shape of the permanent magnet; figure 91 shows a cross-section of a variant of the embodiment of figure 85 in which the magnet is received in an undercut space in a plastic sleeve which is welded, for instance ultrasonically, into a non-undercut cylindrical cavity in a plastic pressing ring part; and

figure 92 show s a bottom view of the pressing ring part according to figure 91.

Attention is drawn to the fact that figures 1 and 14, figures 3 and 15, figures 37 and 56 (on smaller scale) and also figures 38 and 39 are shown together on the same scales on respective pages by way of comparing the known art and the invention, and by way of illustrating the extremely compact construction of the coupling according to the invention compared to the prior art and the very small number of components of the coupling according to the invention compared to the known art.

By way of comparison to figures 24, 25 and 26, figure 57 is also shown on the same page as these figures.

Figure 1 shows a coupling 1 from the manufacturer Vector (trade name) between two more or less cylindrical tubes 4, 5 through which medium can flow via respective throughflow spaces 2, 3 and in which a sealing ring 8 deformed under pressure is situated between the mutually facing end zones 6, 7 of the two tubes 4, 5, whereby as a result of end zones 6, 7 being moved toward each other with some force during the assembly of coupling 1 the coupling 1 has become medium- tight, peripheral laterally protruding parts or flanges 9, 10 are formed integrally on both end zones 6, 7, on the mutually facing sides of which two tubes end surfaces 11, 12 are present, pressing means in the form of a rim of bolts 13 and associated nuts 14 are present which co-act with the flanges 9, 10 placed prior to realizing of coupling 1 in at least roughly aligned positions relative to each other and hold them pressed toward each other while retaining the deformation of sealing ring 8, and locking means also formed by bolts 13 and nuts 14 for maintaining the relative position of flanges 9, 10 pressed toward each other and so also maintaining the medium -tight coupling realized between tubes 4, 5. In the embodiment according to figure 1 coupling 1 comprises four bolts 13 and nuts 14. The bolts extend through at least roughly aligned through-holes 15, 16 in the respective flanges 9, 10.

Further tubes 17, 18 are welded to tubes 4, 5 via orbital weld zones 45, 46. These comprise inward oriented flat contact zones between tubes 3, 4 and tubes 17, 18 and V-shaped grooves on the outer side thereof. The V-shaped grooves have a depth in the order of magnitude of half the local wall thicknesses and are filled with welding material through a welding operation.

Figure 2 shows the coupling according to figure 1 in full lines. The broken lines show, in highly exaggerated manner for the sake of clarity, the mechanical deformation of flanges 9, 10 under the influence of the pressure of the medium in throughflow spaces 2 and 3. Shown in exaggerated and therefore somewhat symbolic manner is that end surfaces 11, 12 tend to move apart under the pressure of the medium, thereby causing a risk of leakage in that the pressure on sealing ring 8 becomes lower due to the medium pressure.

Attention is further drawn to the fact that in coupling 1 at the position of the sealing ring the flow of the medium is greatly impeded locally by the peripheral recess, since in this commercially available coupling 1 the radially furthest inward peripheral circular surface of sealing ring 8 lies radially further outward relative to central axis 19 than the walls of tubes 4 and 5. As a result of this obstacle the extremely undesirable phenomenon can occur during throughflow of medium under pressure at high flow rate that coupling 1 produces a very irritating or loud sound, for instance a very sharp whine at a frequency in the order of 5 kHz, and at sound pressure levels at a distance in the order of 1 to 2 m of up to 115 dB SPL.

It is noted that the coupling according to figures 1 and 2 is commercially available and is applied on a large scale. The associated drawbacks are tolerated for lack of better solutions in the prior art.

Figure 3 is a perspective view of coupling 1 . The arrangement of bolts 13 and nuts 14 can be clearly seen herein, as can the holes 15 in flange 9. It should be appreciated that during assembly of coupling 1 one nut 14 is first slightly tightened, then the diagonally opposite nut and subsequently one of the other nuts, followed by the diagonally opposite nut, after which the whole procedure is repeated one or more times until the torque wrench being used indicates that all nuts have been tightened with substantially the same torque. This final torque is predetermined. It will be apparent that during successive assembly of a large number of such couplings the human factor in the form of a lack of concentration or fatigue can begin to play a part, whereby it occurs in practice that couplings are not assembled with the required care and accuracy.

Figure 4 shows a coupling 20 according to the invention. Components of this coupling 20 corresponding to those of coupling 1 according to figures 1, 2 and 3 are designated with the same reference numerals as therein.

Other than in the case of coupling 1 according to figures 1, 2 and 3, end surfaces 11, 12 are in direct contact with each other. Present in end zone 6 is a peripheral recess which is positioned concentrically relative to central axis 19 and debouches on end surface 11. As shown particularly clearly in figure 5, an O-ring 21 is located in recess 20. In the case where this O-iing is manufactured from for instance rubber or a rubber4ike material, and is therefore substantially non- compressible, the volume of ring 21 must be slightly smaller than the volume of recess 20. This ensures that end surfaces 11, 12 can come into contact with each other, hi the compressed state according to figure 5 sealing ring 21 does not therefore completely fill recess 20. Some space is left clear.

In the case where nuts 14 have been tightened with a sufficiently great torque, coupling 22 is highly resistant to bending moments. This is a result of the fact that end surfaces 11, 12 of the tubes 4, 5 generally consisting of metal will not deform, or hardly so, in the case of a bending moment, in contrast to coupling 1 in which tubes 4, 5 are in contact with each other via sealing ring 8 which displays a certain degree of defonnability and therefore tends to be compressed on one side under the influence of a bending moment.

Figure 6 shows a variant in which complementary rotation-symmetrical registering steps

23 connect to end surfaces 11, 12. These ensure that the cylindrical inner walls of throughflow spaces 2, 3 are exactly aligned relative to central axis 19 and that no disruption whatever of the throughflowing medium can therefore occur at the position of the transition between end surfaces 11, 12. In the case of flat surfaces 11, 12 as according to figure 5 special measures must be taken in order to ensure this exact positioning. The registering steps 23 according to figure 6 are therefore strongly recommended.

Figure 7 shows a coupling 28 which is free of bolts and nuts and which can be assembled with a high degree of accuracy and reliability with little or no professional skill and does not have the above described drawbacks of the known art, or hardly so, such as coupling 1 and even the simple embodiment of the coupling 22 according to figure 4.

Components corresponding functionally to each other are also designated in this figure 7 with the same reference numerals as in the foregoing figures. It is noted that the relevant components need not be of the same shape but do fulfil the same functions.

In coupling 28 the end zones 6, 7 of tubes 4, 5 have peripheral protruding parts 24, 25. These have on their sides facing away from each other truncated conical first contact surfaces 26, 27 which have the same shapes but are in opposed orientation. During assembly of coupling 28 the contact surfaces 26, 27 are urged toward each other in axial direction, so along central axis 19, by urging in radial direction toward each other the parts, with the same radial section at each position, of a divided pressing ring consisting in this case of two parts 29, 30 and having a peripheral internal recess with two mutually facing truncated conical second contact surfaces 31, 32, the shape and inclination of which correspond to those of first contact surfaces 26, 27. After the end surfaces 11, 12 have been thus pressed with force against each other as a result of the inward directed displacement of pressing ring parts 29, 30, a locking ring 33 serving as locking means is finally arranged over the outer surfaces of pressing ring parts 29, 30.

It is noted for a good understanding that end surfaces 11, 12 determine the assembled positions of all the components involved. The pressing ring parts are after all pressed toward each other with compression of the O-ring 21 until end surfaces 11, 12 are in contact with each other. This means that the furthest inward partly cylindrical surfaces 34, 35 and also the partly cylindrical inner surface 36, 37 of the recess defined by pressing ring parts 29, 30 must remain located some distance from the outer surfaces of respectively tubes 4, 5 and the peripheral protruding parts 24, 25. Figure 7 shows coupling 28 in assembled state in which the above is clearly shown. Owing to the pressing ring parts 29, 30 being pressed toward each other with a sufficient force by means of a tool, in combination with the angle of inclination of the co-acting contact surfaces 26, 31 and 27, 32 shown in figure 7, the friction between these contact surfaces holds the coupling in its assembled state, even without locking ring 33 being necessary for this purpose. It will however be apparent that for a system loaded by medium pressure, such as coupling 28, it is not possible to depend solely on friction for the sealing of the coupling. The use of a locking ring 33 is therefore mandatory under all conditions in respect of the required safety.

The half-apex angle of the imaginary cones defined by surfaces 26, 27, 31 and 32 amounts in this embodiment to about 70°.

Attention is further drawn to the fact that, other than in the above shown and described couplings 1 and 22, the use of registering steps 23 as according to figure 6 is not strictly necessary. Owing to the rotation symmetry the system is as it were self-positioning during assembly of the coupling. As a result of the pressure forces and friction forces which occur the peripheral protruding parts 24, 25 will move themselves to the position aligned around central axis 1 shown in figure 7.

Present in the peripheral transition areas where there is a possibility of notch effect are peripheral hollow recesses which act against notch effect and which are all designated 38. Possible formation of notches under strain of bending is hereby effectively prevented.

Figures 8 and 9 show an alternative coupling which differs from coupling 28 according to figure 7 in the sense that the first contact surfaces 26, 27 and the second contact surfaces 31, 32 are parts of jacket surfaces of imaginary cones on which complementary co-acting screw threads are superimposed, whereby conical screw couplings are formed. The screw threads, all designated with reference numeral 40, on the generally truncated conical contact surfaces 26, 27, 31, 32 have a form and relative angular position such that their axial projections exactly coincide. Although the screw thread profiles have rounded shapes and are relatively shallow, for instance have a sine- shaped profiling, a highly pressure and tension-resistant coupling can be realized with the shown construction owing to the angles of contact surfaces 26, 27, 31, 32, which in this embodiment amount to about 45°.

Because it is essential that the screw threads always have the same angular position, coupling 39 is provided with rotation locking means for the purpose of blocking the relative rotation of the protruding parts 24, 25 particularly during, but also after, assembly of coupling 39. End surface 12 has for this purpose two locking pins 41, 42 which fit tightly into correspondingly shaped blind holes 43, 44 debouching on end surface 11. Because it is essential never to make the mistake during assembly of unintentionally rotating the tubes 4, 5 for instance 180° relative to the nominal position, whereby the screw connection with the conical screw threads cannot be brought about, locking pins 41, 42 and the associated blind holes 43, 44 are positioned such that they fit into each other in only one angular position. This angular position corresponds to the assembled form of coupling 39 as according to figure 8. Pressing the pressing ring parts 29, 30 toward each other following an initial rough positioning enables the pressing ring parts 29, 30, in this pressed- together situation, to be rotated together through a certain angle, optionally even after locking ring 33 has been arranged, this with a force such that end surfaces 11, 12 arc brought into contact with each other while compressing O-ring 21. The coupling is hereby completed. Owing to the nature of the screw coupling applied, in particular such a coupling as according to EP-B 2 268 930, there need be no fear of loosening of the thus realized, highly pressure-resistant tube coupling.

Attention is drawn to the fact that locking ring 33 in the embodiment according to figure 7 has a round form while locking ring 33 according to figures 8 and 9 has in this embodiment a hexagonal form corresponding to the outer surface of the assembled pressing ring parts 29, 30.

Figures 10 and 11 show a coupling 121 which largely corresponds to coupling 28 according to figure 7, but which differs therefrom in the sense that contact surfaces 1, 32 have shapes corresponding to the function f(x) = sin²Vx.

It is noted that in figures 10 and 11 those components corresponding to those according to figure 7 are designated with the same reference numerals as therein.

Figures 12 and 13 show a variant of coupling 121 according to figures lO and 11. Coupling 122 comprises pressing ring parts 29, 30 which, in contrast to coupling 121 according to figures 10 and 11, are provided with complimentary screw threads on the inclining, rounded contact surfaces 26, 27 such that an at least more or less conical screw coupling is created therewith.

As in the case of coupling 39 according to figures 8 and 9, tubes 4, 5 are locked against relative rotation by means of pins 41, 42 which co-act with holes 43, 44. The main shape of contact surfaces 26, 27 corresponds to that of the corresponding contact surfaces of coupling 121. An at least more or less conical screw thread is however superimposed on these contact surfaces. These conical screw threads of the peripheral protruding parts 24, 25 have coinciding axial projections. This is a condition for making it possible to ensure that, when pressing ring parts 29, 30 are rotated, the screw threads can function correctly such that tubes 4, 5 are urged toward each other until end surfaces 11, 12 make contact with each other. It is noted here that the mutually facing, in this case substantially radially oriented surfaces 301, 302 may not make contact with each other on at least one side, since otherwise there is a danger of end surfaces 11, 12 not making contact with each other, and this would be contrary to the teaching of the invention.

Figure 14 shows a tube coupling 47, the main construction of which corresponds to that of coupling 28 according to figure 7. For the purpose of an absolutely certain accurate alignment use is made in this embodiment of the rotation-symmetrical registering steps 23, whereby the peripheral protruding parts 24, 25 are precisely aligned relative to central axis 19. Figure 15 is a perspective view of coupling 47 according to figure 14. It is important to note that figure 14 is drawn to the same scale as figure 1. The same applies for figures 3 and 15. When prior art coupling 1 is compared to coupling 47 according to the invention it is immediately noticeable how much simpler, smaller, lighter and easier to assemble coupling 47 is than coupling 1.

Figure 16A shows a coupling 48 which corresponds in significant part to coupling 28 according to figure 7 but differs therefrom in the sense that end surfaces 11, 12 have registering steps 23. An extremely accurate alignment is hereby ensured relative to the central axis 19 of the walls of throughflow spaces 2, 3 without the risk of there being any obstacle at the position of the transition between the two. Attention is drawn to the fact that the radial surfaces 11, 12 are in contact with each other and that the radial annular surfaces 54, 55 of step 23 are located some distance from each other. This ensures that, as described above, surfaces 11, 12 are in contact with each other.

Figure 16B shows that the peripheral protrusion 24 can be provided at the position of registering step 23 with a peripheral positioning edge 49.

Figure 16C shows a variant in which the peripheral protruding part 25 is provided with a positioning edge 50.

Figure 16D shows a combination of the aspects according to figures 16B and 16C, wherein the peripheral protrusion 24 is provided with a positioning edge 49 and the peripheral protrusion 25 is provided with a positioning edge 50.

The use of positioning edges has the advantage that the peripheral protrusion 24 and 25 can be placed more easily in their exact registered positions.

Figure 17 is an exploded view of the coupling 48 according to figure 16A. This view corresponds to a drawing of the situation in which the constituent parts of coupling 48 have not yet been put together to form an assembled coupling, but in which they are in the preliminary stage of assembly.

During the assembly process the peripheral protruding parts are first placed substantially in register against each other, whereby sealing ring 21 is not yet compressed, or hardly so. Pressing ring parts 29 and 30 are then moved toward each other such that the first contact surfaces 26, 27 come into contact with second contact surfaces 31, 32, whereby these surfaces slide over each other and an axial pressing movement takes place wherein end surfaces 11, 12 are moved with force toward each other while deforming the sealing ring 21. As soon as end surfaces 11, 12 are in contact with each other, locking ring 33 is pushed over the now assembled pressing ring parts 29, 30. Coupling 48 is hereby assembled.

Figure 18 shows a coupling 51 which is in significant part the same as coupling 48 according to figure 13, but differs therefrom in the sense that the protruding parts 24 and 25, in contrast to coupling 48 according to figure 13, do not have a freely selectable angular position but can be fixed in only two angular positions. The inner surfaces of pressing ring parts 29 and 30 are for this purpose provided with a key, both of which keys co-act in locking manner with keyways 52 in the form of continuous recesses 52 which extend in axial direction and into which keys 53 fit with small clearance. Following assembly, coupling 51 can be used for instance as drill shank for extracting mineral oil and gas.

Figure 19 shows highly schematically the manner in which couplings 48 or 51 can be realized. As described above, as final step locking ring 33 must be pushed with a quite

considerable pressure force over the outer surfaces of the assembled pressing ring parts 29, 30. Used for this purpose is a tool which, on the basis of for instance electrical or hydraulic actuation, moves two forks 56, 57 with force toward each other. Use is made in the drawn embodiment of a hydraulic cylinder 58 which is actuated by a hydraulic pump 59.

Fork 56 engages on the outer side of the peripheral protruding part 24, while fork 57 engages on the furthest outward rear edge 60 of locking ring 33.

It is appropriate here to draw attention to the presence of two positioning zones 61, 62 on respectively the front and rear side of locking ring 33 in for instance figures 17 and 19 respectively. These positioning zones have an outward widening form, whereby in the situation according to figures 17 and 19 the locking ring 33 can easily be initially pushed via the front positioning zone 61 over the outer surfaces of pressing ring parts 29, 30 onto the correct location. Owing to the pressure force exerted on forks 56, 57 by actuation of hydraulic cylinder 58 the locking ring 33 is thus pushed with force into the position shown for instance in figures 8, 10, 12, 14, 15, 16A. The associated coupling, in this case coupling 48, is hereby completed. Actuation of pump 59 can be ended and the hydraulic cylinder can be moved back to its starting position.

Figure 20 shows the situation in which the positioning zone 61 has just passed over the front edge of the outer surfaces of pressing ring parts 29, 30 and is being pressed further as according to arrow 63.

Figure 21 shows the situation prior to removal of locking ring 33 using an axially divided tube part 303 and the tool according to figure 19.

Figure 22 shows that in the situation according to figure 16D the sealing ring in the form of O-ring 21 is accommodated substantially undeformed in recess 20.

Figure 23 shows the situation in which protruding parts 24, 25 have been moved toward each other until their end surfaces 11, 12 make contact with each other, hi this situation sealing ring 21 has been compressed into the shape shown in figure 23 in which it fills recess 20 for the major part but in which some free space nevertheless remains. This free space is shown with reference numerals 64 and is located in the four corner zones. Figure 24 shows by way of illustration a completely impractical embodiment in which the centre of the round O-ring 21 lies outside end surface 11. When protruding parts 24 and 25 are moved toward each other there is a great risk of the sealing ring 21 being pinched between the sharp edges of recess 20 in protruding part 24 and the opposite recess 20' co-acting therewith in protruding part 25.

Figure 25 shows an embodiment in which the risk of pinching is substantially wholly precluded. The edges of recesses 20, 20' are for this purpose chamfered and rounded. These edges are all designated with reference numeral 65.

Figure 26 shows a variant in which the round sealing ring 21 lies so deeply in recess 20 that its centre lies inward relative to end surface 1 1. It will be apparent that there need be no fear of the ring being pinched here when end surfaces 1 1, 12 are moved toward each other.

Figures 27 and 28 show parts of a coupling 66. This relates to tubes 4, 5 with their respective peripheral protruding parts 24, 25 and sealing ring 21, while pressing ring parts 29, 30, see for instance figure 7, are omitted for the sake of clarity.

Coupling 66 differs from coupling 28 according to figure 7 in the sense that end surfaces

11, 12 have a wave-shaped, in particular sine-shaped profiling pattern 166 relative to respective main planes extending at least more or less transversely of the axial direction. The peripheral recess 20 is located in a peripheral zone 67 which is free of such a profiling.

Tubes 17, 18 connecting to tubes 4, 5 are welded to the free ends of these latter over weld zones 45, 46.

Figure 29 shows an embodiment in which sealing ring 68 is hollow and consists of a material, for instance metal, which is inherently stiff and tensively strong compared to rubber and which in this embodiment is provided with a relatively deformable cover layer or a cover layer 69 of a material with a lower yield point than the material of the sealing ring.

The wall of the sealing ring has on its side facing toward throughflow spaces 2, 3 in the area of end surface 11 a pressure-equalizing slotted hole 70 extending over the whole periphery.

Figures 3 OA and 30B show a variant in which a sealing ring has a rim of pressure- equalizing holes 72.

Figures 31 and 32 show a tool for placing accurately in register with each other and temporarily holding the tube 5 with the peripheral protrusion 25 integrally formed thereon and the tube 18 to be welded thereto. It is noted that tubes 5 and 18 have identical dimensions.

The two tubes are laid in the manner shown in figure 31 against each other and supported by a V-shaped trestle 72 shown in figure 32. Following this positioning the relevant end zones of tubes 5 and 18 are pressed against trestle 72 by tightening a clamping screw 73 via a clamping block 74 which has a lower surface with a curvature adapted to the curvature of tubes 5, 18. The tubes are thus located with their end surfaces against each other and fixed in this position. With a simple welding operation the hereby resulting V-shaped groove 75 already described in the foregoing can be filled with welding material, and tubes 5, 18 are thus welded partially to each other, at least to the extent the weld zone is accessible. As soon as the welding operation has progressed such that the tubes are fixed non-releasably to each other, the tubes 5, 18 welded fixedly to each other can be removed from clamping device 72, 73, 74 and the welding operation can be completed. Alternatively , the clamping force of screw 73 can be reduced to some extent, whereby the combination 5, 18 can be rotated and the orbital welding operation can thus be completed.

Figure 33 shows an embodiment in which the end zones of tubes 5, 18 are provided with registering steps 77, 78 connecting to the inclining surfaces 75, 76 of the V-groove, whereby tubes 5, 18 can easily be exactly registered, optionally even without use of clamping device 72, 73, 74. Here too at least one of the edges of steps 77 and/or 78 could be provided with a chamfered positioning edge.

Figure 34 shows a structure wherein a compression fitting is added on both sides of the tube coupling according to figures 14 and 15.

These compression fittings, which are designated with reference numerals 79 and 80, are identical. Only compression fitting 80 will therefore be discussed here.

Arranged around tube 18 is a so-called ferrule 81. This has an outward narrowing form and co-acts in that area with a correspondingly formed sleeve 82 with external screw thread which co- acts with a cap 83 which undergoes an axial displacement during rotation and thus exerts a pressure force on ferrule 81 via a pressing ring 84. Sleeve 82 can be coupled with its end zone 85 with conical screw thread to a further tubular element. When cap 83 is rotated with force the pressing ring and the ferrule are subjected to a great pressure force. Since they are enclosed between the cap and sleeve 82, they both have only one possible manner of deforming and thus reducing the applied pressure, i.e. deforming of tube 18 in the area of pressing ring 84 and the tapering end zone of ferrule 81. A very great pressure force is thus exerted on tube 18, whereby tube 18, which can for instance be manufactured from steel or copper, deforms in elasto-plastic manner. Compression fitting 80 is hereby realized.

Figure 35A shows a coupling 86 which can be deemed a variant of coupling 48 according to figure 16A. The right-hand part of coupling 86 is the same as the right-hand part of coupling 48. The left-hand part is however configured for coupling to a flexible conduit or hose 87. This hose 87 is pushed over tube 4 as far as an annular stop surface 88 and the radially furthest inward edges of pressing ring parts 29, 30 press hose 87 with force sealingly against the outer surface of tube 4. For an optimum seal and a high degree of tensile strength the tube 4 is provided with an annular thickened portion 89 which co-acts via hose 87 with the associated peripheral end edge 90 of pressing ring parts 29, 30. Figure 35B shows a part of coupling 86 according to figure 35A on larger scale such that the details are more clearly visible. Attention is drawn to the fact that the peripheral end edge 90 is situated in the assembled form of coupling 86 on the right-hand side of the annular thickened portion 89 and comprises two annular ribs.

Figure 36 shows a tube coupling 123 which can be deemed a two-sided, substantially symmetrical embodiment of coupling 86 according to figure 35. In order to underline this symmetry the relevant components which are identical but placed in mirror image are designated on both sides with the same reference numerals.

Figure 37 shows a known commercially available hose coupling 333 from the

manufacturer Gardena/Husqvarna (trade names). Drawn adjacency of figure 37 is a hose coupling 323 according to the invention, which for the purpose of comparison to hose coupling 333 according to figure 37 is drawn on the same scale as coupling 333. It is evident that coupling 323 according to the invention is very considerably more compact than prior art coupling 333.

Figure 38 is an exploded view of coupling 333. Shown on the same page is an exploded view of coupling 323 according to the invention as shown in longitudinal section in figure 56.

Noticeable in addition to the already mentioned compactness is that the number of components of the coupling according to the invention is very substantially smaller than the number of components of prior art coupling 323.

Figure 39 is an exploded view of coupling 323 according to the invention. Figure 39 is drawn on the same scale as the exploded view of prior art coupling 333 as shown in figure 38.

It should be understood that figure 37, the adjacent figure 56 and figures 38 and 39 are drawn on the same scale.

Figures 37 and 38 show prior art hose coupling 333. Figures 39 and 56 show hose coupling 323 according to the invention on the same scale. To the left of centre of the coupling in figures 38 and 39 the diverse components are shown coupled to hose 87. On the right-hand side the hose is shown separated from the components which are shown in exploded view. Hose 87 is pushed over tube stub 307 in the area of a rim of resilient plastic tongues 308 which, when a screw cap 309 is screwed on in axial direction, undergo a radially inward displacement and so clamp hose 87 fixedly on tube stub 307. Tongues 308 are formed integrally with the plastic component 310 to which three barbs 311 are added as separate components which co-act with a peripheral edge 312 of a coupling piece 313. An O-ring 314 is added on each side to coupling piece 312. Extending around a part of the component 310 and coupling piece 330 is a release sleeve 315 which is loaded by a compression spring 316 in the direction of a central flange 317 which fon s part of coupling piece 313. By moving release sleeve 315 outward with some force in the direction of hose 87 counter to the action of spring 316 the barbs 311 are relieved of tension and can thus pass freely over the annular widened portion or edge 312 in backward direction such that the complete unit 318 (see the left-hand part of coupling 333 shown in integrated form in figure 38) can be detached from coupling piece 313.

Attention is further drawn to the fact that an O-ring 314 is added on both sides to coupling piece 313. These O-rings are pushed with some elastic elongation over the ends of tube stubs 326 and accommodated in respective peripheral recesses 327.

Compression spring 316 is on the one hand enclosed on either side between a peripheral stop surface 328 on the inner surface of release sleeve 315 and a peripheral stop surface 329 which forms part of a flange 330 present on the outer surface of component 310.

The positioning of barbs 311 is ensured by three pairs of positioning ribs 331.

Figures 39 and 56 show coupling 323 according to the invention. Immediately noticeable is the great simplicity of this coupling in combination with its spectacular compactness compared to the prior art coupling 333.

Coupling 323 comprises to coupling parts 319, 320 with tube stubs 321 over which hose 87 is placed. For mutual coupling the coupling parts 31 , 320 are moved toward each other such that the mutually registered sealing rings 21 make contact, or at least substantially make contact, with each other and end surfaces 11, 12 therefore lie in register opposite each other. Pressing ring parts 29, 30 are then placed and manipulated in the manner already described above such that an axial displacement of coupling parts 319, 320 toward each other takes place until end surfaces 11, 12 come into contact with each other with elasto-plastic deformation of the sealing rings.

Other than in the many exemplary embodiments described above and shown in the drawings, pressing ring parts 29, 30 are, although similarly formed, are in this embodiment not separate of each other but connected pivotally to each other by means of a hinge 322 extending in axial direction. It is possible here to envisage for instance a film hinge in the case where the whole pressing ring 29, 30, 322 is manufactured as injection-moulded component from plastic. Reference is made for the operation in principle of the pressing ring parts to, among others, the coupling 28 according to figure 7.

Other than is the case with the foregoing exemplary embodiments, pressing ring parts 29, 30 comprise co-acting locking means which are integrated with these pressing ring parts. It is hereby possible to dispense with the use of a locking ring. Pressing ring part 29 thus comprises a resilient locking tongue with a first hook part and pressing ring part 30 comprises a locking protrusion co-acting therewith and having a second hook part. By pivoting the pressing ring parts 29, 30 with force toward each other in the described situation the end surfaces 11, 12 are moved toward each other counter to the elasto-plastic deforming forces of sealing rings 21, and hooks 324, 325 snap over each other such that the connection is locked. The connection can be released by moving the end of tongue 324 outward with sufficient force in roughly radial direction, whereby said hooks disengage, the locking ring releases, can be removed and coupling parts 319, 320 are separated from each other.

Particularly, though not exclusively, with reference to the throughflow coupling 323 according to figures 39 and 56 it is noted that on one of the two sides a coupling part 319, 320 can form part of or be coupled to a tap, in particular an outdoor tap, wherein hose 87 is for instance a garden hose. The coupling of a coupling part to the tap can optionally take place by making use of an adapter which can be screwed on one side onto the external screw thread of a known outdoor tap, or the relevant coupling part forms part of the tap itself.

It will now be apparent that coupling 323 according to figures 39 and 56 need only consist of three parts, in particular injection-moulded parts and at least one, but preferably two identical and mutually registered sealing rings. This latter is important because different components have to be coupled in completely random manner, which is not compatible with the use of two types of component. Envisaged as material is PA (nylon), PC (polycarbonate), ABS or such superior plastics. The use of an inferior material such as PVC is rejected in principle. PVC is in general a material which is too soft, vulnerable and subject to rapid ageing and fatigue. When the stated superior materials are used fibre reinforcement will not be necessary in most common applications.

It will otherwise be apparent that other known construction materials, such as brass, can also be applied for more stylish embodiments or more exacting applications.

As shown particularly clearly in figure 56, hoses 87 are held under pressure between annular thickened portions, in which respect reference is made by way of comparison to figures 36,

40, 41, 42. An extremely tensively strong connection is hereby guaranteed and the coupling can also withstand very high medium pressures. This is otherwise in the case of coupling 333 according to figures 37 and 38, where the hose is engaged locally by the inward oriented thickened portions on resilient tongues 308.

Coupling piece 313 according to figure 37 has a central flange 317 formed unitarily with the coupling piece. Flange 317 extends peripherally in transverse direction relative to the central axis of the structure.

In coupling 333 according to figure 37 the screw cap 309 is provided internally with a truncated conical pressure surface which, during rotation for the purpose of clamping each of the two hoses 87, scrapes with great force over the outer surfaces of resilient tongues 308. These tongues are manufactured from PVC and have only a limited mechanical strength and resistance to scraping. PVC is a relatively soft plastic. Owing to this scraping with great force over the outer surfaces of resilient tongues 308 they are not only forced radially inward but are also loaded laterally with great force relative to their longitudinal direction, so in tangential direction. Tongues 308 are thus heavily loaded mechanically during rotation of screw cap 309 in a manner for which the tongues are essentially not configured both in terms of material choice and form. The service life of these tongues is hereby limited. In practice therefore the tongues break off after a number of said rotations of screw cap 309. It will be apparent that this has a greatly adverse effect on the lifespan of coupling 333. This is highly disadvantageous for the consumer, as it will be apparent that the coupling 333 constructed from many complicated injection-moulded parts is by no means cheap.

Comparison to the coupling 323 according to the invention, which is shown in among others figure 36, shows that this coupling not only takes a very considerably simpler form but moreover has no components which rotate and/or scrape against each other. Coupling 323 according to the invention will thus have a very considerably longer service life than prior art coupling 333.

Reference is further made, perhaps unnecessarily, to the exploded views of respectively coupling 333 according to figure 38 and coupling 323 according to the invention as shown in figure 39.

In anticipation of the further variants of the coupling according to the invention to be described below it is noted that figures 58-84 show important variants of the coupling according to the invention. It will become apparent on the basis of the description of these figures that particularly this coupling according to the invention can be closed and opened very easily and highly reliably without this adversely affecting the service life of the couplings.

Figure 40 shows a coupling 124 which differs from coupling 123 according to figure 36 in that pressing ring 29, 30 comprises two pressing ring segments 125, 126 separated in axial direction, each of which segments is assembled from at least two pressing ring parts. The locking ring, which in the coupling 123 according to figure 36 and all the couplings described and drawn prior thereto consists of one part, takes a divided form in the coupling 124 according to figure 40. It consists of two locking ring parts 33a and 33b which are separated in axial direction and which co-act with the two respective pressing ring segments 125, 126. Pressing ring segments 125, 126 are connected to each other in the manner shown in figure 40 by means of an at least more or less conical screw connection 127. This is preferably of the type as described in the above

specification. Using such a superior screw connection a very firm screw connection can be realized by a relative rotation of pressing ring segments 125, 126 of only a fraction of a revolution, for instance in the range of 90-180°. In order to perform such a rotation it is recommended that the outer surfaces of pressing ring segments 125 and 126 are non-round, for instance have a hexagonal form. Prior to the rotation each pressing ring must be assembled by mutually connecting pressing ring parts 29, 30 by means of the respective locking ring parts 33a and 33b. These have a shape modified to the non-round form of the outer surfaces of pressing ring segments 125, 126.

Attention is drawn to the fact that pressing ring segments 125 and 126 are provided with rims of shallow recesses 135, whereby during mutual coupling of pressing ring segments 125, 126 by rotation a user has a firm grip thereon. It is noted that such shallow recesses are generally known per se.

Figure 41 shows a hose coupling 134 which is largely similar to coupling 124 according to figure 40 but differs from this coupling in the sense that locking ring parts 33a and 33b fit tightly round each other in the manner clearly shown in figure 41 and thus contribute toward the permanent coupling between pressing ring segments 125 and 126.

Figure 42 shows a hose coupling 136 which differs from couplings 124 and 134 according to the respective figures 40 and 41 in the sense that the peripheral end edges 90, which each comprise two peripheral ribs, are situated on the outer side relative to the annular thickened portion 89.

Other than in couplings 124 and 134, where locking ring parts 33a and 33b consist of spring steel or other suitably strong material, locking ring 137 of coupling 136 according to figure 42 consists of a silicone rubber. Any potential relative rotation of pressing ring segments 125, 126 is hereby effectively prevented due to friction contact. Attention is drawn to the fact that due to the nature of the conical screw coupling, which has already been discussed above, there is no need to fear detaching of the coupling. Under very extreme conditions, in particular a very strong impact load, it is however possible to envisage the conical coupling becoming detached. The locking ring 137 of silicone rubber effectively prevents this, and in a very simple manner.

It is noted that in the embodiments according to figures 40 and 41 the annular thickened portion 89 is situated outward relative to end edges 304 of pressing ring parts 29, 30. In the embodiment according to figure 42 this relative placing is reversed. In this embodiment the annular thickened portions 89 lie inward relative to end edges 304. Attention is further drawn to the fact that end edges 304 take a dual form. The local contact pressure on hose 87 is hereby increased.

Attention is further drawn to the fact that in all couplings according to the invention, wherein the pressing ring parts are coupled to each other by means of a conical screw coupling, these pressing ring parts preferably have a non-round outer surface and use is made of a correspondingly shaped non-round locking ring, or use is made of recesses 135, whereby a user has a better grip on the relevant pressing ring parts to be rotated relative to each other. For heavier constructions, which can only be assembled with a relatively great force, it will in some circumstances not be possible to couple the pressing ring parts to each other by hand. Use must then be made of two co-acting tools. It is then recommended for this purpose to make use of non- round outer surfaces.

Referring to figure 42 it is further noted that the silicone rubber locking ring 137 can have a small thickness. It can in that case be easily rolled over the assembled coupling. This arranging is facilitated by the slight barrel shape shown in figure 42.

The silicone rubber locking ring 137 also acts as impact protection. Figure 43 shows a coupling of 190 which combines a number of aspects of for instance coupling 28 according to figure 7 and compression fittings 79 and 80 according to figure 34.

Other than in the tube couplings according to the invention discussed in the foregoing, the peripheral protruding parts 24, 25 are not connected non-releasably to tubes 4, 5 but are embodied as separate rings with the same shape as for instance the peripheral protruding parts 24, 25 in coupling 28 according to figure 7. Parts 24, 25 are slidable over tubes 4, 5.

A sleeve 1 serving as sealing ring extends over the end zones of tubes 4, 5. This sleeve 91 lies tightly over the outer surfaces of the end zones. The two side zones 92, 96 of the sleeve, i.e. the zones on either side of the central zone thereof, narrow toward their free ends. Sleeve 91 is accommodated in the peripheral recesses 93, 94 which connect to end surfaces 11, 12 of protruding parts 24, 25. These recesses 93, 94 are the same as each other. The central zone of sleeve 91 has a peripheral inner flange 95 which extends inward from its inner surface and which in this embodiment extends over the whole wall thickness of tubes 4, 5 between the end surfaces of these tubes and is in pressure contact therewith. As described above, end surfaces 1 1 , 12 are urged toward and brought into contact with each other under the influence of the radial movement of pressing ring parts 29, 30 toward each other such that the axial displacement of protruding parts 24, 25 toward each other during assembly of the coupling deforms said side zones 92, 96 of sleeve 91 radially inward, whereby the end zones of tubes 4, 5 also deform inward locally. These annular deformations are retained after assembly of coupling 190 under the influence of the action of pressing ring parts 29, 30 and the locking ring 33 arranged tensioned around them. The two tubes 4, 5 are thus coupled sealingly to each other while making use of sleeve 91 by two compression fittings which are the same and placed symmetrically relative to the mutually facing end surfaces of tubes 4, 5.

Figure 44 shows by way of illustration a graph in which three tension curves are shown, i.e. the tension curve 97 of steel, the tension curve 98 of aluminium and the tension curve of copper and silver. It is noted that for the sake of clarity the curves are drawn only by way of indication and that the actual tension curves have other shapes.

The tensile stress σ, expressed in N/mm², is plotted vertically and the elongation ε in horizontal direction in %.

The tension curve 97 of steel has three parts. The elastic part 100 has a very great inclination in accordance with the E-modulus of steel. It will be apparent that the steepness of part 100 is such that it cannot be drawn to scale in this figure. Connecting to the elastic part is a part of more or less constant tensile stress in which the elongation increases. To the part with roughly constant tensile stress connects the final part 102 of the tension curve. Here can be seen a gradual rise to a maximum tension, followed by a decrease in the tensile stress to the breaking point 103. If in the area 102 the tensile stress were to be reduced to zero, the material will not then return to the value σ=0 and ε=0, so the origin of the graph, but retains a plastic deformation, whereby in the transition from area 102 to area 101 it returns as according to the broken line 104 to a new rest value ε₀ corresponding to the pennanent plastic defonnation of the material. Lines 100 and 104 run parallel.

The tension curve 98 of aluminium initially also displays an clastic behaviour of the material, i.e. the elastic part 105, which has a smaller angle of inclination than that of the elastic part 100 of steel, in accordance with the lower E-modulus of aluminium. The rest 106 of the tension curve connects thereto. It will be apparent that steel is a substantially stronger material than aluminium. The elongation at break of aluminium is considerably greater than that of steel, as can be seen from the location of breaking point 107.

The tension curve 99 of copper, which largely corresponds to that of silver, shows that this material is even softer than aluminium and has an elongation at break 108 corresponding to an even greater s than the point 107 for aluminium.

On the basis of this qualitative representation of several material properties of steel, aluminium, copper and silver it appears that for instance copper would be possibly suitable as material for the sealing ring. Copper displays a behaviour other than for instance steel as according to curve 97. The tension curve 99 of copper shows that the elasticity modulus, i.e. the tangent of the angle of inclination at small ε, is considerably smaller than the tangent of the angle of inclination of the elastic part 100 of tension curve 79 of steel, which complies with Hooke's law. With continued stretching the tension in the material increases only to limited extent and the elongation at break 108 is considerably greater than the elongation at break 103 in the case of steel. Copper is thus found to be a material which deforms elasto-plastically relatively easily. In accordance with the teaching of the invention it is hereby possible to realize that a sealing ring of copper deforms relatively easily and can shape itself extremely well to even very small unevenness on the surface of the material which bounds the peripheral recess in which the sealing ring is accommodated. Envisaged here are small surface roughnesses and even crystal surfaces which can be very troublesome in the case where a good seal is required.

Figure 45 shows a coupling 112 which forms a variant of coupling 190 according to figure 43. In coupling 112 the peripheral recesses 93, 94 take a bent form such that they initially accommodate the narrowing side zones 92, 96 of sleeve 91 with some clearance, wherein as in the case of coupling 190 the volume of sleeve 91 is smaller than the space bounded by the peripheral recesses 93 and the outer surfaces of tubes 4, 5. By pressing end surfaces 11, 12 against each other in the above described manner the end zones 92, 96 press against tubes 4, 5 with a great force such that they deform plastically and the compression fitting is realized.

Figure 46 shows on larger scale the described structure of sleeve 91 with inner flange 95 and outer flange 109 in the assembled state of coupling 112. It will also be apparent that peripheral recesses 93, 94 have a form such that particularly the narrowed end zones of side zones 92, 96 are under strain of pressure and the local pressure on tubes 4, 5 therefore becomes so large that the tubes become plastically deformed locally.

hi the case of couplings 90 according to figures 43, 45 and 46 and coupling 212 according to figures 45 and 46 the inner flange 95 extends over the whole wall thickness of tubes 4, 5. The form of flange 95 is such that the throughflowing medium does not encounter any disruptive transition.

Figure 47 shows an alternative of sleeve 91 in which the flange is received in a V-shaped groove 212 which has the same shape as the flange and which is formed by the oblique end surfaces of tubes 4, 5.

Figure 48 shows a further variant in which flange 95 is likewise received in a groove 112 which has the same shape and which, at variance with figure 47, extends only to about halfway along the thickness of the walls of tubes 4, 5. The remaining parts of the flat end surfaces of tubes 4, 5 press against each other.

Figure 49 shows very schematically a jet engine 113 known from the literature. It is known that all sections of jet engines are normally coupled to each other with flange connections with bolts and nuts. They are hereby subject to the limitations described above with reference to figures 1, 2 and 3 which show very schematically elements of the prior art.

Several flange connections according to the described prior art are all designated in figure 49 with reference numeral 114. The designations 114 are however given only by way of indication. Every jet engine, in particular jet engines for passenger aircraft, have many tens of flange connections of the described type according to the prior art. Because jet engines always involve high-tech structures which are heavily loaded thermally and in respect of pressure, the most extreme care is taken in the design and during the manufacture of a jet engine to guarantee the safety of every jet engine as far as possible, also in the very long term. It must after all be remembered that jet engines represent a significant factor in the safety of passengers and crew.

Figure 50 shows the manner in which an engineer 128 couples two segments 130, 131 of a jet engine housing to each other by means of a flange connection 129 with bolts 13 and nuts 14 in the manner as indicated with reference to figure 1. The engineer 128 must arrange the bolts and nuts in extremely careful manner through the pre-registered holes in flanges 9, 10. These are placed very precisely in register beforehand by means of locating pins. Even the arrangement of the through-holes for receiving the bolts must take place meticulously, and even then it is not wholly possible under all circumstances to prevent a slight shift occurring on the inner surfaces of segments 130 and 131 at the position of the coupling, which in the case of the extreme flows as in jet engines could cause turbulence and flow losses. From the realistic representation of the work of the engineer 128 for assembling a flange coupling with bolts and nuts between two jet engine segments 130, 131 it should be apparent that the work of the engineer is highly demanding. He/she will sometimes have to take up very strange positions during the assembly of the coupling because the segments supported by trestles 305 are fixedly disposed and the engineer must therefore often bend over or work above his/her head or choose a working position as well as possible making use of a ladder device.

It will be apparent, for instance by comparing figures 1 and 14, that the very protracted and highly exacting work of the engineer 128 according to the prior art as shown in figure 50 can be replaced with very great technical and economic advantage by arranging the simple coupling of the type as shown in figure 14. Advance reference is made in this respect to the following discussion of figures 51 and 52.

Figure 51 shows coupling 114 of the type as usual in jet engines 113. As always in this specification, components in figure 51 which correspond functionally to components of coupling 1 according to figures 1 , 2 and 3 are designated with the same reference numerals as therein An exception is made for the gasket ring which is designated in figure 1 with the reference numeral 8 and in figure 51, so in the case of coupling 114, with the reference numeral 115. This is because ring 11 differs very substantially in form from ring 8. It not only extends over the full wall thickness of tubes 4, 5 but also over the whole of the mutually facing end surfaces 11, 12 of peripheral flanges 9, 10.

Situated between flange 9 and bolt head 116 is a locking ring 117. Likewise situated between flange 10 and nut 14 is a locking ring designated with 118. Owing to this structure scoring during tightening of nuts 14 and optionally bolt heads 116 relative to flanges 9, 10 is prevented. In addition, rings 117, 118 can be provided in per se known manner with a rim of oblique tongues which prevent unintended loosening of the nuts relative to bolts 13.

Figure 52 shows on the same scale as the prior art coupling 114 as drawn in figure 51 a coupling 119 as inventive alternative according to the invention to coupling 114. Coupling 119 has a structure which corresponds to that of coupling 47 according to figures 14 and 15. Attention is drawn to the fact that tubes 4, 5 are placed in register relative to each other via registering steps 23.

It will be apparent that use of coupling 119 as replacement for prior art coupling 114 in jet engine 113 will result in very great advantages. An immediately obvious advantage is that couplings 119 can be assembled with a considerably increased accuracy in a substantially shorter time than the couplings of the type 114. Since what is involved here are large rims with bolts, for instance of a diameter in the order of 2.5-3 m, and the number of bolts per coupling is often in the order of 50-150, and also taking into account the fact that there are many tens of such couplings, it will be apparent that, by making unnecessary the successive tightening of the nuts several times according to a very closely regulated and controlled protocol followed by a very precise inspection and follow-up checks, the relatively simple procedure for assembling the coupling according to the invention results in extremely great economic advantages. Added to this is that with the coupling according to the invention a very significant source of possible malfunctions and failure is eliminated, i.e. the human factor in the fomi of the engineers who have to arrange and nuts using torque wrenches and other advanced equipment. In addition, the coupling according to the invention requires very considerably less material than the prior art coupling. Reference is made in this respect to a comparison between coupling 1 14 according to figure 51 and the coupling 119, drawn on the same scale, according to figure 52. Because the coupling according to the invention can be so much lighter, a considerable weight-saving will also be possible. Finally, attention is drawn to the fact that the coupling according to the invention can be manufactured in considerably shorter time than the prior art coupling. Orders can thus be filled in a shorter time.

Figure 53 shows a coupling 219 which can be deemed as a hybrid form of coupling 90 according to figure 43, which is based on the principle of the compression fitting, and coupling 39 according to figures 8 and 9 in which use is made of conical screw threads between the peripheral protruding parts 24, 25 and the pressing ring parts 29, 30.

Coupling 219 is assembled in the same way as coupling 90, with the understanding that the peripheral protruding parts 24, 25 are separately slidable over tubes 4, 5 as according to figure 43 and are locked for rotation in the manner of figure 8 by locking pin 41 which is accommodated fittingly in the blind hole 43.

Other than in the case of coupling 90, the pressing ring parts 29, 30 are not pressed radially toward each other but are brought with their internal conical screw threads 40 into engagement with the corresponding complementanly formed conical screw threads 40 on the corresponding inner surfaces of pressing ring parts 29, 30.

When realizing the coupling 119 the pressing ring parts 29, 30 must first be assembled to form one pressing ring. This takes place by arranging locking ring 33. After this locking ring 33 has been arranged, a rotation force is exerted with a tool on pressing ring 29, 30. As a result of the effect of the relative action of the screw threads a displacement of the protruding parts 24, 25 directed axially toward each other hereby takes place. Further reference is made in this respect to the description of figure 43.

In the manner described above with reference to figures 8 and 9, joint rotation of pressing ring parts 29, 30 with force brings about the coupling by the peripheral protruding parts being pressed together axially until end surfaces 1 1, 12 are in contact with each other. The compression fitting is hereby wholly assembled.

Figure 54 shows a coupling 220, the structure and operation of which largely correspond to those of coupling 1 19 according to figure 53, with the understanding that the form of sleeve 91 and the forms of the peripheral recesses 93, 94 are the same as those shown in figures 45 and 46 for coupling 212.

Figure 55 shows the manner in which the assembly of coupling 219 or coupling 220 is completed by sliding with force over the outer surfaces of pressing ring parts 29, 30 the hexagonal locking ring 33, the form of which corresponds to the hexagonal outer form of the assembled pressing ring parts 29, 30. Reference is otherwise made to the description of figure 19. It is noted that fork 56 is provided on both its legs with pressure plates 120 which, prior to sliding on of locking ring 33, co-act in pressing manner with the associated outer surfaces of pressing ring parts 29, 30. Pressing ring parts 29, 30 are thus held in their desired relative position in which locking ring 33 can be pushed thereover. Before or optionally after this the thus mutually connected pressing ring parts can be rotated with force, whereby as a result of the presence of the co-acting conical screw threads 40 the coupling 219 or 220 is assembled in sealing manner.

Everywhere where this is technically appropriate, the zones under strain of bending with surfaces connected to each other via diagonals can be provided with peripheral recesses acting against notch effect. These peripheral hollow recesses with a smooth rounded shape are designated everywhere in the drawings with the reference numeral 38.

Figure 57 shows a variant in which the peripheral protruding parts 24, 25 are identical but placed mirror-symmetrically and each provided with the same peripheral recess 20, 20' in which identical sealing rings 21, 2Γ are accommodated. When a coupling is closed the flat end surfaces 11, 12 lie against each other and O-rings 21, 2 Γ are compressed, while some free space filled with air remains in cavities 20, 20'.

Figure 58 corresponds to figure 39. At variance with figure 39, the hose 87 on the right- hand side is shown in the situation coupled to coupling part 320. This is the situation in practice in which the user, after coupling hoses 87 to coupling parts 319, 320, need only couple the coupling parts firmly and sealingly to each other by means of locking ring 30, 31.

Figure 59 shows in cross-section that the resilient tongue 324 is provided on its inner side with a locking protrusion 401 which is displaceable together with tongue 324 and which in the coupled situation of figure 59 is urged inward under the spring force of resilient tongue 324 and so hooks behind the fixed locking protrusion 402 formed together with the lower locking ring part 30. In this situation the coupling has been realized and it can only be uncoupled by engaging the end zone 402 of tongue 324 and displacing it outward in more or less radial direction such that locking protrusion 401 disengages from the fixed locking protrusion 402. As soon as this co-action is ended, the locking ring parts 29, 30 can be folded open again around film hinge 322 to the position shown in figure 58 in which coupling parts 319, 320 are each free.

Figure 60 shows a variant of coupling 29, 30 in which use is not made of a film hinge 322 but of a hinge 404 with a hinge pin 405. Such a hinge can be applied in the case where the use of a film hinge is not appropriate, for instance in the case metal is used as material for locking ring parts 29, 30.

Figure 61 shows locking ring 29, 30, 404, 405 in cross-section. With the exception of hinge 404, this corresponds exactly to the locking ring drawn in figure 59.

Figure 62 shows a variant in which a resilient tongue 406, which in principle corresponds functionally to resilient tongue 324 according to figures 58 and 59, is not provided on its inner side with only one displaceable locking protrusion 401 but with a number of such locking protrusions, all designated with 407. These together form a ratchet which, during pressing of the locking ring parts 29, 30. are in successive ratcheting co-action with the fixed locking protrusion 402 until the desired pressing force has reached its maximum value and the coupling is completed.

Figure 63 shows a cross-section of the variant according to figure 62.

It will be apparent that, by displacing end zone 403 outward, the coupling can be released in all three of the above described embodiments.

Tn the embodiment according to figures 58-63 the resilient tongues 324, 406 do not protrude outside the substantially cylindrical main outer surface of the assembled locking rings 29, 30. These tongues are accommodated in a correspondingly formed recess 408 which provides sufficient space not only to accommodate the resilient tongue 324, 406 but also to engage the end zone 403 of the relevant resilient tongue, for instance using a finger or a screwdriver.

Figure 64 shows an embodiment in which the locking ring parts consist of two separate, albeit identical parts 29, 30. On each side the embodiment corresponds in principle to the embodiment according to figures 58 and 59. Other than in this embodiment, each of the two locking ring parts 29 comprises a resilient tongue 324 which, similarly to the embodiment according to figures 62, 63, co-acts with the fixed locking protrusion 402 which forms part of the other locking ring part. It will be apparent that the coupled state can be obtained by displacing the locking ring parts 29, 30 as according to figure 64 toward each other.

Release of the coupling according to figure 65 can again take place by first displacing an end zone 403 of a resilient tongue 326 outward, after which the same operation can be performed on the other side of the locking ring.

Figure 66 shows a variant in which locking ring parts 29, 30 are provided with a strap construction of for instance a tensively strong plastic. Extending on the upper locking ring part 29 from film hinge 322 is a tensively strong plastic strip 410 which is provided on the outer side with teeth or ridges 409 and which can be inserted into a coupling sleeve 411 of per se known structure with barb means on the inner side which can co-act with the teeth or ridges 409 acting as barbs. Coupling sleeve 411 is formed integrally on the end of a second strip 412 which is fixedly connected to the lower locking ring part 30 adjacently of film hinge 322. In the coupled situation of figure 67 the strap 410, 411, 412 is accommodated in a substantially peripheral recess 413 such that it falls within the more or less cylindrical outer main surface of coupling 29, 30.

It should be understood that the coupling according to figures 66 and 67 is for once-only use and, following tightening of strip 40 with force through coupling sleeve 411, can no longer be removed other than by cutting through one of the strips 410, 412.

Figures 68 and 69 show a variant in which use is made of a similar principle as in figures 66 and 67, be it that the coupling according to figures 68 and 69 can be reopened after having been closed. Attached for this purpose to each of the locking ring parts 29, 30 is a part of a hook/loop tape combination. Figure 68 shows that a hook tape element 414 is fixedly attached in a recess 413 in the lower locking ring part 30 while a first part of a loop tape element 415 is attached in the same recess 414 in the upper locking ring part 29 and protrudes therefrom, as shown in figure 68, in the opened position of the locking ring and can be brought into co-action with hook tape element 414 after the locking ring elements 29, 30 have been moved with force toward each other to the closed position of figure 69. From the closed position shown in figure 69 the locking ring can be opened again by gripping the end of the hook tape element 414 and moving it outward in the per se known manner, whereby the coupling to the loop tape element 414 is lost.

Figures 70 and 71 show a variant in which locking ring parts 29, 30 remain closed under the influence of the force of co-acting strong permanent magnets, in particular neodymium magnets 416, 417; 418, 419. As is known, the smaller the distance between the north and south poles of magnets, the greater the force becomes with which the two poles attract each other. In the case drawn in figure 70 the distance can and even must be small but not completely zero since end surfaces 11, 12 of the coupling pieces must after all rest against each other in accordance with the teaching of the invention. If magnets 416, 417; 418, 419 were to rest against each other, said end surfaces 11, 12 would not rest against each other, and this would be contrary to the invention.

After reaching the closed position shown in figure 71, pressing ring parts 29, 30 can be removed from each other again by placing a screwdriver (not shown) between edge recesses 420, 421 and performing a rotary movement therewith with some force. A great force can hereby be exerted such that this exceeds the attractive force between magnets 416, 417; 418, 419, whereby the coupling is opened and the opened position according to figure 17 is obtained.

Figures 72 and 73 show an embodiment which corresponds in significant part to the embodiment according to figures 70 and 71, but differs therefrom in the sense that edge recesses 420, 421 extend to a greater depth and moreover extend laterally between the magnet poles 416, 418; 417, 419.

Added to pressing ring 29, 30 is a tool 422 using which the pressing ring can be opened easily from its closed position, even more easily than by rotating a screwdriver as described with reference to figures 70 and 71. Tool 422 comprises a ferromagnetic tongue 423 which is supported by a handle 424. The ferromagnetic tongue 423 can be inserted into the mutually connecting edge recesses 420, 421 of the closed pressing ring 29, 30. These edge recesses 420, 421 have the same shape as the front edge of ferromagnetic tongue 423. The magnet poles 416, 418; 417, 419 are magnetically short-circuited by inserting this tongue 423 into the common edge recesses 420, 421, whereby their attractive force is reduced substantially to zero. The insertion movement is indicated with an arrow 425. Following the insertion as according to arrow 425 as described above and the neutralizing of the attractive forces between said magnets, the pressing ring can be opened by a rotation of handle 424, and thereby of tongue 423, as according to an arrow 426 so that pressing ring parts 29, 30 are separated from each other.

Figures 74, 75 and 76 show a pressing ring 427, of which the component pressing ring parts 29, 30 carry generally U-shaped magnets 428, 429.

Situated in a largely cylindrical assembled edge recess 430, 431 is a manually rotatable operating wing 432 of ferromagnetic material. In the shown position the operating wing extends at a distance from the poles of magnets 428, 429. By way of elucidating the placing of these poles reference is made for the sake of convenience to the similar placing according to figures 70 and 72. In this position the operating wing is magnetically passive. It can be rotated as according to an arrow 433 to a position in which, similarly to the inserted ferromagnetic tongue 423 according to figure 72, it is effectively active as magnetic shunt and thus reduces the attractive magnetic forces between magnets 428, 429 to negligible proportions.

In order to allow the pressing ring parts to pivot around hinge 322 and so separate the parts from each other and release the coupling, the operating wing 432 can be rotated according to arrow 433 further from the position indicated with 434, whereby with a continued powerful rotation around rotation shaft 435, which is connected to the upper pressing ring part 29, it can set itself off against a step 436, owing to which mechanical force pressing ring parts can be separated from each other into the opened position similar to that shown in figures 70 and 72.

The outer surface of pressing ring part 29 is marked with indicators 437 for the closed situation and 438 for the opened situation of the pressing ring.

Figures 77, 78, 79 and 80 show a pressing ring 29, 30, the functionality of which corresponds to pressing ring 29, 30 according to figures 74, 75, 76, but differs therefrom in the sense that a ferromagnetic shunt 439 can be displaced by a wingnut and bolt head 440 in longitudinal direction between the passive position shown in figures 78, 79 and 80, in which shunt 439 lies outside the range of magnets 428, 429, and an active position in which shunt 439 extends between the magnet poles 428, 429 and short-circuits the magnetic field, hi the active position the attractive force between magnets 428, 429 is maximal and pressing ring 29, 30 can only be opened by exerting a correspondingly great force. In the passive position the attractive force between magnets 428, 429 is practically zero and the force needed to open the pressing ring is small. In the passive position described in the previous sentence the force necessary to open the pressing ring is limited to overcoming the Coulomb friction between the truncated conical first contact surfaces 26, 27 on the one side and the second contact surfaces 31, 32 on the other, for which reference is made for the sake of clarity to figure 7. It is noted here, perhaps unnecessarily, that in order to realize the coupling according to figure 7 and all other embodiments with such co- acting truncated conical first and second contact surfaces, the locking ring parts 29, 30 must be moved with some force toward each other in order to overcome the Coulomb friction. It may even be desirable in some circumstances to give these pressing ring parts a light tap, for instance with a plastic hammer, whereby they in fact become firmly fixed, even in the absence of the locking ring 33 to be arranged later.

As soon as the attractive force between magnets 428, 429 has become zero in said passive position, the Coulomb friction between said first and second contact surfaces must be eliminated, which can for instance take place by inserting and rotating a screwdriver as according to figures 70 and 71 , inserting and rotating the tool 422 as according to figures 72 and 73, rotating the operating wing 432 with force so that it sets itself off against step 436 as according to figures 74, 75 and 76, and making use of continued rotation of rotatable carrier 446 as according to figures 81-84 to the position in which the magnets repel each other with great force. All these stated auxiliary means contribute toward overcoming said Coulomb friction forces, and being able to remove the locking ring parts from each other with relative ease in order to release the coupling.

The translation of shunt 439 takes place in that, locked against rotation, it co-acts in the manner of a nut with a threaded end 441 arranged fixedly on the wingnut. The displacement in the longitudinal direction takes place by rotating the wmgnut between positions 437 and 438.

Figures 81, 82, 83, 84 show yet another embodiment of a pressing ring. In this embodiment each of the pressing ring parts 29, 30 is provided with bar magnets. The lower pressing ring part 30 carries two bar magnets 444, 445 embedded fixedly in the plastic of pressing ring part 30, while the upper pressing ring part 29 has a rotatable carrier 446 in which are embedded bar magnets 442, 443 disposed in exact register relative to magnets 444, 445. In said registered state according to figure 83, pressing ring 29, 30 is in its closed and locked position. A rotary knob 447 formed integrally on rotatable carrier 446 is therefore oriented toward the marking 437 "closed" as shown in figure 81. By rotating rotary knob 447 through 90° to the marking 438 "open" the pairs of magnets 442, 443 are rotated through 90° relative to magnets 444, 445. This is the wholly neutral central position in which the attractive force between the respective magnets 442, 444 and 443, 445 is in principle reduced to zero. As shown in figure 81, the outer surface of the upper pressing ring part 29 has a third marking 448. In the situation corresponding thereto the magnets 442, 443 have changed places relative to the position shown in figure 83. The oppositely oriented and therefore attracting respective magnets 442, 444 and 443, 445 are now replaced by the respective repelling pairs 443, 444 and 442, 445. In this position there is no longer a neutral situation free of forces, but the magnets exert a very strong repelling force on each other whereby the pressing ring parts 29, 30 can be separated from each other without the least effort to a position similar to that according to figures 70 and 72.

It is noted that use could also be made in the embodiment according to figures 81, 82, 83,

84 of generally U-shaped magnets. This is not strictly necessary. Use is after all preferably made of permanent magnets of neodymium. Neodymium is an extremely powerful permanent magnetic material and the addition of extra magnetic mass and weight provides only little advantage relative to the bar magnets in the present embodiment.

Figures 85 and 86 show a pressing ring part or a rotatable carrier 29, 30, 446 in which in an undercut cavity a correspondingly shaped permanent magnet 449 is embedded in the plastic of the associated component. The magnet is placed therein as insert during the injection moulding. Figures 87 and 88 show a variant in which a magnet 450 has a rotation-symmetrical form with a number of protruding rounded flanges, and is thus embedded as insert in the same manner as magnet 449 in the associated plastic during injection moulding of component 29, 30, 446.

Figures 89 and 90 show that it is not strictly necessary under all conditions to make use of undercut forms. A magnet 451 has a prismatic form, i.e. it has the same diameter at any axial position. The cross-section can be seen in the bottom view according to figure 89. A generally cylindrical shape is supplemented with six rounded ribs extending in longitudinal direction of magnet 451. The hereby resulting greatly enlarged surface area is sufficient in practice to realize an adhering force of magnet 451 in the material of component 29, 30, 446 such that, when the magnet means of a pressing ring described in the foregoing are removed from each other, there need be no fear of the relevant magnet becoming detached from the associated plastic.

Figures 91 and 92 show a variant of the embodiment of figures 85 and 86 in which magnet 449 is embedded in a cylindrical plastic sleeve 452 which is subsequently welded, for instance by a welding process such as ultrasonic welding, into a correspondingly shaped cylindrical cavity in component 29, 30, 446.

It will be apparent that all four exemplary embodiments according to figures 85-92 guarantee a very strong attachment of magnets 449, 450, 451 in the plastic of component 29, 30, 446 and that this ensures that there are no practical conditions whatever in which the relevant magnets can come loose under the influence of the high attractive magnetic forces which can occur during opening of the associated pressing ring.

hi all embodiments the end surfaces of the peripheral protruding parts are preferably in contact with each other with all their overlapping parts.

The hardness of the sealing rings is selected on the basis of the application of the coupling according to the invention.

Claims

Claims

1. Coupling between two elongate tubular or rod-like elements through which medium can optionally flow via respective througliflow spaces, such as tubes, tube stubs, pipes, vessels, bodies, shafts, bars, with a common central axis, wherein

a sealing ring deformed under pressure is situated between the end zones of the two elongate elements, whereby the coupling has become medium-tight as a result of the end zones being moved with some force toward each other during assembly of the coupling;

peripheral laterally protruding parts are added to both end zones;

end surfaces are present on the mutually facing sides of both elongate elements and/or of both protruding parts;

pressing means are present which co-act with the protruding parts brought into at least roughly mutually aligned positions prior to realizing of the coupling and which hold these pressed toward each other while maintaining the deformation of the sealing ring;

locking means co-acting with the pressing means are present for the purpose of maintaining the relative position of the protruding parts pressed toward each other and thus also maintaining the realized medium -tight coupling between the two elongate elements;

the sealing ring is accommodated in a peripheral recess in at least one of the end surfaces; the end surfaces have complementary forms at least over corresponding peripheral zones; the end surfaces are in direct contact with each other at least in said peripheral zones under the influence of the pressing means; and

the sealing ring is embodied such that in the assembled state of the coupling it is deformed elasto-plastically under the influence of the pressing force exerted by the pressing means and has shaped itself in dominant measure to the shape of the peripheral recess(es) while leaving clear some free space;

characterized in that

the protruding parts have on their sides remote from each other rotation-symmetrical first contact surfaces which widen in the direction of the end surfaces and which have the same shapes but an opposite orientation;

during assembly of the coupling the contact surfaces are urged in axial direction toward each other by urging in radial directions toward each other the parts, with the same radial cross- section at each position, of a divided pressing ring consisting of at least two parts and having a peripheral internal recess with two mutually facing second contact surfaces which are substantially complementary to the first contact surfaces, and the form and inclination of which correspond to those of the first contact surfaces; and after the end surfaces have been thus pressed against each other a locking means is activated, for instance a locking ring serving as locking means is arranged over the outer surfaces of the pressing ring parts.

2. Coupling as claimed in claim 1, wherein the protruding parts arc connected non- movably to the associated elongate elements.

3. Coupling as claimed in claim 2, wherein the protruding parts are formed integrally with the associated elongate elements or connected non-re leasably thereto.

4. Coupling as claimed in claim 1, wherein the protruding parts are separate of the elongate elements and are coupled thereto by the pressure forces exerted by the pressing means.

5. Coupling as claimed in any of the foregoing claims, wherein the or each recess lies symmetrically relative to the central axis.

6. Coupling as claimed in any of the foregoing claims, wherein the elongate elements are tubular, and the open ends of the two throughflow spaces have the same shapes and the tubular elements are placed in register such that the walls of the two throughflow spaces connect substantially smoothly and evenly to each other.

7. Coupling as claimed in any of the foregoing claims, wherein

the pressing ring comprises two pressing ring segments which are separated in axial direction and which are each assembled from at least two pressing ring parts;

the locking ring comprises two locking ring parts which are separated in axial direction and which co-act with the two respective pressing ring segments; and

the pressing ring segments are connected to each other by means of an at least more or less conical screw coupling.

8. Coupling as claimed in claim 7, wherein

the one pressing ring segment has an external screw thread and another pressing ring segment has an internal screw thread complementary thereto,

the screw threads are superimposed on two for instance truncated conical base surfaces monotonously narrowing and widening respectively in the direction of a central axis,

the longitudinal section of each of the screw threads relative to the central axis is a periodic univalent function which is continuous at least at the inflection points, the first derivative of the longitudinal section of each screw thread along the base surface is a continuous function;

the second derivative of the longitudinal section of each screw thread along the base surface is a continuous function;

the second derivative of the longitudinal section of each screw thread relative to the central axis is a continuous function at least in the region of the inflection points;

the function is calculated on the basis of a Fourier series; and

the harmonics above a chosen maximum ranking number, for instance 5, are ignored; as a result of which the screw threads are in mutual contact over a substantial surface area differing from line contact.

9. Coupling as claimed in any of the foregoing claims, wherein the locking ring comprises a monocrystalline material, for instance monocrystalline steel or carbon.

10. Coupling as claimed in any of the foregoing claims, wherein the locking ring comprises fibres with high tensile strength, for instance of glass, carbon, boron, aramid, reinforced PE (polyethylene).

11. Coupling as claimed in any of the foregoing claims, wherein the first and the second contact surfaces both have a truncated cone shape.

12. Coupling as claimed in any of the foregoing claims, wherein

the one pressing ring part comprises at least one first permanent magnet, for instance of neodymium; and

the second pressing ring part comprises at least one other permanent magnet co-acting with the first permanent magnet, or a ferromagnetic anchor.

13. Coupling as claimed in any of the foregoing claims, wherein the pressing ring consists of two pressing ring parts which each cover an arc of 180°.

14. Coupling as claimed in any of the foregoing claims, wherein all pressing ring parts are identical.

15. Coupling as claimed in any of the claims 7-14, wherein the first and the second contact surfaces are parts of the jacket surfaces of imaginary cones, the half-apex angle of which has a dimension (90-X)°, wherein X has a value such that the pressing ring parts, after being pressed onto the protruding parts, remain in position thereon under the influence of the friction between the contact surfaces, and lies particularly in the following ranges, stated in order of preference, of 55°- 85°, 60°-80°, 65°-75°, 67°-73°.

16. Coupling as claimed in any of the foregoing claims, wherein peripheral rounded recesses which act against notch effect are present in the annular transition areas between the outer surfaces of the elongate elements and the associated first contact surfaces.

17. Coupling as claimed in any of the foregoing claims, wherein peripheral rounded recesses which act against notch effect are present in the annular transition areas between the surface extending between the second contact surfaces and these second contact surfaces of the pressing ring parts.

18. Coupling as claimed in any of the foregoing claims, wherein

the first and the second contact surfaces have smooth rounded forms and have on their wide end zones and on their narrow end zones mutually coinciding tangential cylinders coaxial with the central axis; and

the first and the second contact surfaces have inflection planes with a truncated cone form which have inflection circles in common with the contact surfaces.

19. Coupling as claimed in claim 18, wherein the contact surfaces have over a substantial area on either side of the inflection circles shapes which at least approximately correspond to the shape of the inflection planes.

20. Coupling as claimed in claim 19, wherein the axial section of each of the contact surfaces satisfies the equation f(x) = A.sin^B πχ, in which

x = the axial location;

A = a constant directly proportional to the radial dimension of the associated contact surface;

B = a power to be selected, in order of preference: B > 10; B > 20; B > 40.

21. Coupling as claimed in any of the foregoing claims, wherein the locking ring parts are in engagement with the protruding parts solely through contact between the first and the second contact surfaces.

22. Coupling as claimed in any of the foregoing claims, wherein mutually co-acting registering steps connect to the end surfaces.

23. Coupling as claimed in claim 22, wherein the registering steps have at least one positioning edge.

24. Coupling as claimed in any of the foregoing claims, wherein the pressing ring parts have a shape widening in radial direction outward and in axial direction to about the radial position of the radial outer edge of the protruding parts such that the local moment stresses in the pressing ring parts are at least more or less constant in the area of the widening form.

25. Coupling as claimed in any of the foregoing claims, wherein

the elongate elements are tubular and have a determined wall thickness; and

the smallest radial dimension of each pressing ring part in the axial area of the largest diameter of the protruding parts is at least approximately as great as the wall thickness of the tubular elements.

26. Coupling as claimed in any of the foregoing claims, wherein the locking ring fits tightly around the assembled pressing ring, optionally with some deformation.

27. Coupling as claimed in claim 26, wherein the locking ring is manufactured by stretching a ring of a steel to the desired circumference while strengthening the material such that the obtained locking ring consists of spring steel with a tensile strength that is increased substantially relative to the original steel.

28. Coupling as claimed in either of the claims 26 and 27, wherein

the assembled pressing ring has a prismatic outer surface and the locking ring has a correspondingly formed prismatic locking ring part;

a peripheral positioning edge connects to the prismatic locking ring part on at least one axial end; and

the prismatic part of the locking ring is brought into its position by passing over the positioning edge and the locking ring being pushed on further in sliding manner, optionally with some force.

29. Coupling as claimed in claim 28, wherein the outer surface has a cylindrical form.

30. Coupling as claimed in claim 28, wherein the outer surface has a non-round form.

31. Coupling as claimed in claim 30, wherein the outer surface has a cross-section with the form of a regular polygon, in particular a hexagon or an octagon.

32. Coupling as claimed in any of the claims 26-31, wherein the locking ring is crimped onto the pressing ring either by first being heated, subsequently being slid into position over the pressing ring and finally being allowed to cool, or by first cooling the pressing ring, for instance using liquid nitrogen, subsequently sliding the locking ring into position over the pressing ring and then heating the pressing ring.

33. Coupling as claimed in any of the foregoing claims, wherein the two protruding parts are locked by rotation locking means against relative rotation around their common central axis.

34. Coupling as claimed in claim 33, wherein the rotation locking means comprise a key coupling between the two protruding parts and at least one pressing ring part.

35. Coupling as claimed in any of the foregoing claims, wherein the peripheral recess has a form relative to the sealing ring such that pinching of the sealing ring between the end surfaces is precluded during assembly of the coupling.

36. Coupling as claimed in claim 35, wherein the sealing ring has a round cross-sectional form, the diameter of which is only a little larger than the radial width of the recess such that, prior to assembly of the coupling, the sealing ring can be pressed with some elastic deformation into the recess and the axial depth of the recess is greater than the cross-sectional radius of the sealing ring.

37. Coupling as claimed in any of the foregoing claims, wherein the material of the sealing ring or an optional cover layer thereof is a natural rubber, a synthetic rubber, a rubber-like material or an elastomer.

38. Coupling as claimed in any of the claims 1-36, wherein the material of the sealing ring or an optional cover layer thereof is a metal which has a lesser hardness and/or a lower yield point than the material of at least the walls of the peripheral recess.

39. Coupling as claimed in any of the claims 1-36, wherein the sealing ring comprises a crystalline material with a cover layer of a rubber-like material or an elastomer, such as PTFE, or copper, silver or babbitt.

40. Coupling as claimed in claim 35, wherein both side walls of the or each recess connect via an outward widening surface to the associated end surface.

41. Coupling as claimed in any of the foregoing claims, wherein the end surfaces are flat and extend perpendicularly of the axial direction.

42. Coupling as claimed in any of the foregoing claims, wherein

the end surfaces have a profile pattern which is wave-shaped, in particular sine-shaped relative to a main plane extending at least more or less transversely of the axial direction; and the or each peripheral recess is located in a peripheral zone free of profiling.

43. Coupling as claimed in any of the foregoing claims, wherein the sealing ring is hollow and consists of a material, for instance metal, which is inherently stiff and tensively strong relative to rubber, optionally with a relatively deformable cover layer or a cover layer of a material with a lower yield point than the material of the sealing ring.

44. Coupling as claimed in claim 43, wherein

the elongate elements are tubular; and

the wall of the sealing ring has on its side facing toward the throughflow space at least one continuous pressure-equalizing hole in the area of the associated end surface.

45. Coupling as claimed in claim 44, wherein the wall of the sealing ring has a rim of pressure-equalizing holes.

46. Coupling as claimed in claim 44, wherein the wall of the sealing ring has a slotted hole extending over the whole periphery of the sealing ring.

47. Coupling as claimed in any of the claims 43-46, wherein the material of a sealing ring consisting of one material or the materials of a sealing ring of laminated construction is/are respectively chosen from the group including: steel, spring steel, Inconel, silver, copper, titanium and alloys on the basis of these materials, such as beryllium copper.

48. Coupling as claimed in any of the foregoing claims, wherein

the elongate elements are tubular; and

a tubular element connecting thereto is connected medium-tightly to the free end of at least one of the tubular elements, for instance is welded thereto.

49. Coupling as claimed in claim 48, wherein the two elongate elements are tubular and have throughflow spaces of the same cross-sectional form, are provided with complementary peripheral registering steps prior to being welded to each other, are slid into each other and subsequently welded to each other over an external orbital weld zone such that the walls of the mutually connecting throughflow spaces connect substantially smoothly and evenly to each other.

50. Coupling as claimed in claim 49, wherein the peripheral end edges of the two elongate elements are chamfered such that they together bound a generally V-shaped peripheral groove which is filled with weld material following the welding operation.

51. Coupling as claimed in any of the foregoing claims, wherein

the elongate elements are tubular; and

a compression fitting is connected to the free end zone of at least one tubular element for the purpose of connection to a further tubular element or a flexible conduit or hose.

52. Coupling as claimed in any of the foregoing claims, wherein

the elongate elements are tubular;

a flexible conduit or hose connects directly to at least one tubular element of the coupling; the conduit or hose is pushed over the outward protruding part of the tubular element as far as a stop surface forming part of the end zone of the associated tubular element; and

the edges of the pressing ring parts located radially furthest inward press the flexible conduit or hose with force sealingly against the outer surface of the end zone of the associated tubular element.

53. Coupling as claimed in any of the foregoing claims, wherein the coupling is designed on the basis of an exact analysis, for instance with a computer and the use of software for perfomiing an iterative, highly non-linear finite element calculation in which the friction forces between the contact surfaces are taken into account.

54. Coupling as claimed in claim 5, wherein

the elongate elements are tubular; a sleeve serving as sealing ring extends over the end zones of the tubular elements;

the sleeve lies tightly over the outer surfaces of the end zones of the tubular elements; the two side zones of the sleeves on either side of the central zone thereof narrow toward their free ends;

the sleeve is accommodated in the peripheral recesses in the end surfaces of the protruding parts;

the recesses are the same as each other;

the central zone of the sleeve has a peripheral inner flange which extends from its inner surface and which extends over at least a part of the wall thickness of the tubular elements between the end surfaces of these elements and is in pressure contact with a least a part of the end surfaces of the tubular elements; and

the end surfaces of the separate protruding parts are urged toward each other under the influence of the pressing means such that the axial displacement of the protruding parts in a direction toward each other during assembly of the coupling deforms the side zones of the sleeve radially inward, whereby the tubular elements also deform inward locally, which deformations are retained under the influence of the pressing means and the locking means following the assembly of the coupling;

this such that the two tubular elements are coupled sealingly to each other while using the sleeve by two compression fittings which are the same and are placed symmetrically relative to the end surfaces of the tubular elements.

55. Coupling as claimed in claim 54, wherein the inner flange extends over the whole wall thickness of the tubular elements.

56. Coupling as claimed in claim 55, wherein the end surfaces of the tubular elements are flat.

57. Coupling as claimed in claim 55, wherein the inner flange extends over a part of the wall thickness of the tubular elements and the end surfaces of the tubular elements are in contact with each other over the remaining part of the wall thickness.

58. Coupling as claimed in claim 55 or 56, wherein the end surfaces of the tubular elements together bound a generally V-shaped groove.

59. Coupling as claimed in any of the claims 54-58, wherein the central zone of the sleeve has a peripheral outer flange which extends from its outer surface and which is accommodated fittingly in an annular cavity which is bounded by two peripheral registering steps which are the same and which connect to the peripheral recesses; such that the outer flange ensures a symmetrical positioning of the protruding parts relative to the end surfaces of the tubular elements during the assembly of the coupling.

60. Coupling as claimed in claim 6, wherein

the first and the second contact surfaces are parts of jacket surfaces of imaginary cones on which complementary co-acting screw threads are superimposed;

the projections in axial direction of the two pairs of complementary screw threads coincide with each other or are rotated through a certain angle relative to each other;

the half-apex angle of the cones has a dimension (90-X)°, wherein X lies in the following ranges, stated in order of preference, of: 35°-55°, 40°-50°, 43°-47°;

rotation locking means are present in order to block the relative rotation of the protruding parts during and after assembly of the coupling; and

the pressing ring parts are pressed toward each other and rotated together with force by means of a tool during assembly of the coupling such that, as a result of the co-action of the conical scre threads, the end surfaces are brought into and, after assembly, held in contact with each other at least in the peripheral zones.

61. Coupling as claimed in claim 60, wherein the rotation locking means are embodied such that they enable only one relative angular position of the protruding parts.

62. Coupling as claimed in any of the foregoing claims, wherein registered peripheral recesses are present in both end surfaces, in each of which recesses a sealing ring is

accommodated, which registered sealing rings co-act sealingly with each other.

63. Coupling as claimed in any of the foregoing claims, wherein the pressing ring parts are connected on the one side by an axial hinge and on the other side comprise respectively a resilient locking tongue with a first hook part and a locking protrusion means with a second hook part co- acting therewith.

64. Coupling as claimed in claim 63, wherein the locking protrusion means comprise a number of at least more or less tangentially disposed second hook parts.

65. Coupling as claimed in any of the foregoing claims, wherein both pressing ring parts comprise a resilient locking tongue with a first hook part and a locking protrusion means with a second hook part, which first hook parts co-act in locking manner with the second hook parts of the other pressing ring part.

66. Coupling as claimed in claim 65, wherein both pressing ring parts are identical.

67. Coupling as claimed in claim 12, wherein

at least one pressing ring part comprises two permanent magnets or a generally U-shaped permanent magnet, the poles of which debouch at the separating surface between the pressing ring parts; and

a ferromagnetic shunt movable from outside by operating means is present which is movable between

a passive position, in which it extends at a distance from the poles and so substantially does not influence the magnetic field between the poles; and

an active position in which it extends between the poles and reduces the strength of the magnetic field substantially to zero.

68. Coupling as claimed in claim 12, wherein

at the separating surface between the pressing ring parts a first pair of magnetic poles debouches at the one pressing ring part and a second pair of magnetic poles debouches at the other pressing ring part; and

at least one of the pairs is movable from outside by operating means between

a first position, in which the pairs attract each other; and

a second position in which the pairs are substantially free of mutual attraction.

69. Coupling as claimed in claim 68, wherein the at least one pair can be moved by the operating means between

the first position;

the second position; and

a third position in which the pairs repel each other.

70. Coupling as claimed in any of the claims 12, 67, 68 or 69, comprising mechanical means for exerting on the two pressing ring parts in the area of the at least one permanent magnet a separating force urging these pressing ring parts apart.

71. Coupling as claimed in claim 70, wherein the mechanical means are also configured to serve as ferromagnetic shunt.

72. Coupling as claimed in claim 70 and any of the claims 67, 68 and 69, wherein the mechanical means arc embodied unitarily with the operating means.

73. Coupling as claimed in claim 68 or 69, wherein the displacement between said positions takes place in transverse direction relative to the magnetic field between the poles.