NZ250931A - Pipe coupling with sealing sleeve held in place by flanged inner and outer casings - Google Patents

Description

Priority Date{3): . nipi^te Specification Filed: c-fc&s: v.?).

Publication Data: ?...§..JAN..I??.?.., P.O. Journal No: 250 93 *» provt«lom of R»g»- 33 (1) th# ®r* Mfc rtun has boon ant^-daie# to ~ ■r— T ^ ^tanjift'. 1 NEW ZEALAND PATENTS ACT, 1953 No. : Date: Divided from New Zealand Patent Specificat: No. 238986 filed 16 July 1991 COMPLETE SPECIFICATION PIPE COUPLING AIL N.Z. PATENT 2 1 FEB 1994 RECEIVLD ^we, TAYLOR KERR (COUPLINGS) LIMITED, a British company of 14-18 Heddon Street, Regent Street, London W1R 7LF, ENGLAND hereby declare the invention for which^Z/we pray that a patent may be granted to pelns, and the method by which it is to be performed, to be particularly described in and by the following statement: - (followed by page la) 25093 - la - o The present invention relates to pipe couplings for connecting together two plain-ended pipes in a fluid-tight manner, of the type consisting of a tubular casing 5 formed with a longitudinal gap, a sealing sleeve of resilient flexible material arranged within the casing, and tensioning means "ior reducing the width of the longitudinal gap. In use, the sealing sleeve is placed around the adjacent pipe ends and the tensioning means 10 are tightened to clamp the sleeve against the outer surfaces of the pipe ends to form a fluid tight seal. jr One known pipe coupling of this type is described in GB - A 1582858. The sealing sleeve is of C-shaped 15 longitudinal cross-section having two lips extending axially inwardly towards one smother so as to form a groove between the extension and the web portion. When the casing is tightened around the pipe ends the lips of the sealing sleeve are pressed into sealing engagement 20 with the outer surfaces of the pipe ends to form a seal. In use fluid carried by the pipes passes through the gap between the pipe ends into the space between the outside of the pipe end and the inside of the web portion of the sleeve. The fluid enters the grooves between the 25 extensions of the lips causing the sealing pressure of the extensions against the pipes to increase as the pressure of the fluid increases.

According, to the present invention there is provided a 30 pipe coupling for coupling together two pipes in a fluid-tight manner, comprising an outer tubular casing, an inner tubular casing located within the outer casing, a tubular sealing sleeve located within the inner casing and means for tensioning the outer casing around the 35 inner casing and the sleeve, the inner and outer casings having inwardly directed end flanges, the tubular sealing sleeve being located between the end flanges of 250931 the inner and outer casing/ the end flanges of the outer casing being adjacent the end flanges of the inner casing and providing lateral support therefor.

Preferably the coupling includes gripping means for securing the pipes axially, the gripping means being located axially inside the flanges of the inner casing. Preferably the gripping means are in the form of toothed rings. By locating all the components inside the inner 10 an.d outer casings and their side flanges a strong and stable structure is achieved.

Preferably the tubular sealing sleeve includes two sets of annular inwardly projecting sealing ribs on the inner 15 surface of the sleeve which engage the respective pipe ends in a fluid tight manner. With this arrangement only the portion of the sleeve between the axially innermost.pair of ribs is exposed to the hydrostatic pressure of the fluid in the pipe. The casing is 20 therefore less prone to bulging at high hydrostatic pressures and, in consequence, the casing can be made of lighter construction than a conventional coupling with the equivalent performance specification. This means that the coupling is less expensive and easier to handle"1 25 during manufacture.

O t Joining together pipes with plain ends with couplings without the need for pipe preparation is quicker and more economical than other methods such as welding, 30 screw threading, flanging, grooving or shouldering.

However because of the enormous axial forces that may be involved in pipelines operating at pressures of say 16 bars, it is difficult to construct a coupling that can reliably withstand such forces.

In the coupling of GB-A-1582858, axial restraint is provided by two frustoconical rings with gripping teeth on their inner edges. The gripping rings are located at 25093 the sides of the sealing sleeve and held in position within the casing by means of snap rings. When the casing is tightened the gripping teeth bite into the pipe ends to provide axial restraint for the pipes.

There are a number of disadvantages with this arrangement. The gripping teeth are sharp and are exposed. This prea ;mts a hazard to the pipe fitters who might cut themselves when handling the couplings prior 10 to, fitting.

The teeth are exposed and may come into contact with water and other corrosive liquids depending on the environment in which they are employed. The teeth are 15 usually made of a hard steel that is prone to crevice corrosion; The geometry of the toothed gripping device is upset on clamping on to the pipe. The specially shaped snap 20 rings that are required to support the gripping rings add to the complexity of the coupling and they only provide partial support for the gripping ring. The snap rings may act as fulcrums over which the teeth are bent" when loaded and there is thus a potential for the teeth" 25 to snap off. '-1 /*. . i / ' • The geometry of the gripping ring is liable to be further upset if a C-shaped sealing sleeve is used for the reasons explained above. The bulging of the casing 3 0 may cause the toothed gripping ring to be lifted out of contact with the pipe leading to failure.

Another type of known coupling is described In GB-A-2167145. This coupling, does not include toothed rings 35 as described above, but it utilises annular sealing members arranged at either end of an annular sleeve, which has wedge-shaped ends. Two flange members fit at either end of the coupling, and a tensioning means is 25093 4 - provided so that the flange members can be urged axially towards one another. This movement compresses the sealing members against the wedge-shaped ends of the sleeve, which in turn forces the sealing members 5 radially inwardly to form a seal against the surface of the pipes.

A plurality of hard gripping members is embedded in each sealing member. Each gripping member has a tooth or 10 teeth formed at one end, and is arranged in the sealing member so WUit_the teeth are flush with, or adjacent, the inner surface of the sealing member. The gripping member is inclined at an angle relative to the axis of the coupling, and the axially outer end of each gripping 15 member is arranged to be completely covered by, but closely adjacent, the outer surface of the sealing member near the corner in the flange member. As the coupling is tightened, the flange members move axially inwardly, compressing the sealing member, and urging the 20 gripping members towards the pipes, causing them to bite into the surfaces of the pipes. Because of the axial displacement between the inner and outer ends of the gripping members, the gripping members will pivot as the sealing member is compressed.

In this coupling, the sealing action of the sealing member against the pipes' surfaces, and the biting ' action of the gripping members are not independent of each other. The gripping members and the sealing 30 members are acted on simultaneously as the flanges are moved axially. Thus the gripping members and the sealing members restrict one another's movement. If the teeth of the gripping member bite the surface of the pipe before the sealing member is properly seated 35 against the surface of the pipe, this could affect the sealing properties of the seal.

According to a preferred embodiment of the present 25093 invention the sealing sleeve has a circumferential slot in its outer surface and a gripping ring with inwardly projecting gripping teeth is located in the slot, the arrangement being such that, in use, tightening the 5 tensioning means causes the sealing sleeve to be pressed into sealing engagement with the pipe ends and the gripping teeth to penetrate the bottom of the slot and to engage the outer surface of the pipe.

Inj a preferred form of the invention a slot with a gripping rincj_.is provided at each end of the coupling. The slot may be frustoconical with the inner end nearer the -^Eucial middle of the coupling than the outer end. The gripping ring is also preferably frustoconical and 15 preferably is an incomplete ring so that it can easily be expanded and compressed.

Preferably, the inner casing fits within the outer casing. The inner casing and the outer casing both have 20 longitudinal gaps and the gap in the inner casing is offset circumferentially from the gap in the outer casing so that the sealing sleeve is supported around its entire periphery either by the inner casing, or the outer casing, or both casings.

By locating the gripping rings in slots in the outer surface of the sealing sleeve the gripping teeth are ... protected and will not injure the pipe fitter when being handled prior to use. 25093 The sealing sleeve may be provided with end seals which form seals between the flanges and the pipe ends. In this way the ingress of water and other contaminants into the seal is prevented, and so the gripping rings 5 are protected from corrosion.

Preferably the slot in the sleeve is wider than the thickness of the gripping rings so that the sealing sleeve does not interfere with the action of the 10 gripping r^ng. The ring is only restrained by the angle of the inner ^and outer casings formed between their tubular walls and their annular flanges. The casing beard directly against the outer edge of the gripping ring. The inner casing bears against the gripping ring. 15 This further reduces the tendency of the outer casing to bulge, compared with a single piece casing.

In the preferred embodiment of the invention the tensioning means applies a radially compressive force to 20 the casing.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, of which:- Fig. 1 shows a perspective cut-away view of a coupling in accordance with the invention; Fig. 2 shows an end view of the coupling of Fig. 1; 2 Fig. 3 shows a longitudinal section through the coupling-30 of Fig. 1; Fig. 4 shows a perspective view of gripping ring of the coupling of Figs. 1 to 3; and Fig. 5 shows a longitudinal section through a coupling similar to the coupling of Figs 1 to 4 hut with a 35 modified sealing sleeve. 25093 A pipe coupling 1 comprises an outer tubular casing 10 an inner tubular casing 20 and a sealing gasket 30. The outer tubular casing 10 is formed of rolled steel, with a longitudinal gap 13. The casing is folded back on 5 itself at its free ends and welded at 14 to form loops 15 along opposite edges of the longitudinal gap 13.

Pins 16 are inserted in the loops. Tensioning screws 17 pass through transverse holes in one of the pins 16 into tapped transverse holes in the other of the pins 16, so 10 as.to interconnect the two free ends of the outer casing. &£cts 18 are cut in the loops 15 so as to provide clearance for the screws. The axial end margins of the casing 1G are beat inwardly at right angles to form radial flanges 19.

The inner tubular casing 20 is of rolled steel and has a longitudinal gap 23. The end margins of the casing 20 are bent inwardly at right angles to form radial flanges 24. The casing 20 fits inside the outer casing 10, the 20 axial length of the casing 20 being slightly less than that of the casing 10 so that the flanges 24 fit inside and, in use, are supported laterally by the flanges 19.

The sealing gasket 30 is o£ rubber formed from a length 25 of flat extrusion which is rolled into a tube and joined by welding to form a complete cylinder. Alternatively, the rubber gasket may be moulded. The outer surface 31 of the gasket is smooth but the inner surface is formed with two sets of annular sealing ribs 32 which project 30 inwardly and have a square profile. In the present embodiment there are three ribs in each set. Towards each end of the gasket the inner surface is stepped inwardly to form lands 33. The extreme ends of the gasket are formed by axial extensions of the inner part 35 of the gasket, which form end seals 34.

The gasket 3 0 fits inside the inner casing with the side flanges 24 fitting into a recess 35 formed behind the 25093 end seals 34.

A frustoconical slot 36 Is formed in the outer surface of the gasket at each end of the gasket. The outer end 5 of each slot lies at the axial end of the outer surface, the inner end of the slot lies close to the inner surface of the land 33. The slope of the slot is such that the inner end is* nearer the axial middle of the gasket than the outer end.

A gripping^ device in the form of a frustoconical ring 40 is .located in the slot 36. The ring 40 is made of hard steel and is an incomplete ring having a gap 41 so that it can be fitted into the slot 36. The width of the 15 slot is greater than the thickness of the steel sheet from which the ring is formed so that the sides of the slot do not interfere with the operation of the ring. The inner edge of the ring 40 is cut at intervals and the portions between cuts are distorted to form teeth 20 42. When the coupling is assembled the teeth sit in the bottom of the slot 36 and the outer edge 43 of the ring sits in the angle formed by the flange 24 on the inner casing.

In use the ends of two plain ended pipes are inserted into the coupling from opposite ends as shown in Fig. 3. A space of say 10mm may be left between the pipe ends to allow for angular deflection, or to avoid abrasive wear, or to dampen vibration. With the coupling in place, the 30 screws 17 are tightened to clamp the coupling to the pipes. As the screws 17 are tightened, the loops 15 of the outer casing 10 are drawn together, thereby applying a radially compressive force to the outer casing. The inner casing is arranged so that its longitudinal gap 23 35 is diametrically opposite the longitudinal gap 13 in the outer casing. In this may the inner casing supports the gasket in the region of the gap 13 where there is to support from the outer casing. The inner casing is 250 dimensioned so that when the coupling is tightened around the pipe ends, then only a small longitudinal gap 23 remains.

The tightening of the tensioning screws 17 presses the annular sealing ribs 32 into sealing contact with the outer surfaces of the pipe ends, the sealing ribs deforming easily due "to their height, width and the grade of material used. At the same time, the gripping 10 ripg 40 is pushed inwardly by the angle of the inner casing gripping the outer edge of the ring. The compression of the gripping ring causes the edges of its teeth 42 to penetrate through the gasket 30 at the bottom of the plot 36 and bite into the surface of the 15 pipe, thereby providing locking of the coupling to the pipe against axial movement. The teeth are designed to make contact at approximately 5mm centres around the circumference with a width of approximately 2mm for each tooth, giving approximately 40% contact around the 20 periphery of the pipe.

The extensions 34 are trapped between the flanges 19 and 24 on the-inner and outer casings and the outer surfaces of the pipe ends to form end seals. Thus liquid and dirt is prevented from entering the coupling from outside. ' ,l t I The coupling described has a number of advantages over known couplings. By using a series of ribs a seal is 30 achieved which is effective at high hydrostatic pressures, for example 16 bars. However, the axial length of the gasket that is exposed to the hydrostatic pressure is small compared with the overall length h of the coupling. This means that the tendency for the 35 casing to bulge is less than with known couplings where almost the entire length of the gasket is exposed to the hydrostatic pressure of the fluid. As a result, the casing of the coupling of the present invention can be 250! of lighter construction than an equivalent conventional coupling. For example, with a coupling for joining together two pipes of around 20cm in diameter, (approximately 8 inches), the thickness of the outer 5 casing can be approximately 3mm, and the thickness of the inner casing approximately 2.5mm. An advantage of using thinner metal is that the machinery required to form the casings is less expensive.

By. locating the gripping ring in a slot in the outside of the gae&etjr, the teeth are protected when the coupling is.not all use and the coupling can be handled easily without a risk of the operator being cut. The resilience of the gripping ring and of the rubber of the 15 gasket causes the teeth to retract back into the slot when the coupling is unfastened so that they no longer project through the inner surface of the gasket. The end seals keep out contamination which right enter the seals from outside and thereby affect performance. The 20 use of low alloy, or high carbon, steel to produce hard teeth on the gripping ring renders them prone to corrosion. The end seals prevent the ingress of moisture, for example sea water, which could cause such corrosion.

The arrangement for holding the gripping rings is of simple construction and apart from the casings and the 2 gasket, involves no separate parts. The entire structure is accommodated within the two pairs of 30 annular flanges 19 and 24 which gives the total structure great strength and stability.

Because of the resilience in the gripping ring and the rubber, the clamping arrangement releases itself when 35 the coupling is released.

The axial restraints operate independent Ay of the gasket. 250931 The teeth do not cut through the gasket entirely, they merely pierce it a 5mm intervals and so the coupling can be repeatedly used.

Because the toothed ring is placed in a wide slot it is free to find its own settlement. The outer edge is located in the angle between the flange and web portions of the inner casing, and the position of the inner edge is merely determined by the position where it bites into 10 th<p pipe. As the coupling is tightened the teeth bite deeper int?o"the pipe. The angle of approximately 45 degrees which is established between the ring and the piper surface when the ring first bites is maintained as the coupling is tightened. The angle in the inner 15 casing bears directly against the outer edge of the gripping ring.

Because the toothed ring bears against the angle in the inner casing, the reaction forces from the toothed ring 20 can be spread through the surface of the inner casing to the outer casing. This further reduces the tendency of *;he casing to bulge, compared to a single piece casing.

Since in the preferred embodiment the seal is not of the 25 C shaped type, it is not dependent on the hydrostatic pressure for effectiveness and therefore the structure is stable in both the charged and uncharged states. Likewise the axial gripping force is independent of the fluid pressure in the pipeline. t Although in the preferred embodiment the teeth are ^ ^ approximately 5mm apart, and each tooth has a width of approximately 2mm, the actual design of the spacing and width of each tooth will depend to some extent on the 35 material from which the pipes are made. Different designs of the coupling can use alternative teeth spacings and teeth widths, depending on the hardness of the pipes for which the coupling is intended. The 25093 sharpness of the teeth may also depend on the material of the pipes for which the coupling is intended. For example, in a coupling intended for joining pipes made of plastics material, the teeth may be blunt. In such 5 an embodiment, as the casing is tightened around the joint, the teeth might not penetrate all of the way through the rubber gasket to bite into the surface of the pipes. In this case, the teeth can still exert sufficient force through the rubber gasket to grip the 10 plastics pipes to axially restrain the coupling on the pipes. r" Although the invention has been described in relation to a coupling for joining pipes of equal diameter it will 15 he appreciated that it can be modified to form a stepped coupling of asymmetric configuration for joining pipes of unequal diameter.

In such a stepped coupling the outer and inner casings 20 would be constructed to extend deeper on tb.e side of the smaller pipe. The gasket would be radially thicker on the side of the smaller pipe, and include a slot, as described above, into which a toothed ring could be fitted. In one form of construction of a stepped 25 coupling, the radial thickness (i.e. the radial dimension from the outer periphery to the inner r;:\'J; fJ periphery) of the toothed ring on the side of the smaller pipe could be greater than that of the other '. V-"] toothed ring. • nUt •/;' Alternatively, the radial thickness of the toothed rings ' ' could he the same, the overall diameter of the ring on the side of the smaller pipe being less than that of the other ring. In this form of construction, the thickness 35 of the inner casing would be increased, on the side of the smaller pipe, so that the respective toothed ring would bear against a portion of the inner casing.

Referring now to Fig. 5, this shows a coupling similar f 250931 to the coupling of Figs 1 to 4 but with a modified sealing sleeve. In Fig. 5 the corresponding elements have the same reference numerals as Figs 1 to 4. The sealing sleeve 30 of Fig. 5 differs from that of Fig. 3 5 in that there is no cavity formed in the region 60 adjacent the ends of the pipes, between the web portion of the sleeve 30 the ribs 32 and the outsides of the pipe ends. Instead the web portion extends inwardly to form an annular land 61 which is pressed against the 10 outside of- the pipe ends when the coupling is tightened around the pipes to form a seal.

The absence of the cavity does not impair the sealing qualities of the coupling and allows the coupling to be 15 used in sanitary applications such as food and chemical processing where the presence of a cavity as in Fig. 3 would preclude the use of the coupling because the fluid passing through the coupling would accumulate in the cavity and could not be cleared out easily by flushing. 20 Typically the width of the land 61 would be 25 to 45mm.

Features of the pipe coupling described above are also described and claimed in our New Zealand Patent Specification Nos 238986, 272180 and 272181.

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Claims (1)

1. WHAT WE CLAIM IS: 1. A pipe coupling for coupling together two pipes in a fluid-tight manner, comprising an outer tubular 5 casing, an inner tubular casing located within the outer tubular casing, a tubular sealing sleeve located within the inner casing and means for tensioning the "outer casing around the inner casing and the sleeve, the inner and outer casings having •'1,511* 10 inwardly directed end flanges, the tubular sealing sle&re being located between the end flanges of the inner and outer casings, the end flanges'1 of the outer casing being adjacent the end flanges^of the inner casing and providing lateral support therefor. A coupling according to Claim 1 including gripping means for securing the pipes axially, the gripping means being located axially inside the_. flanges of the inner casing. A coupling according to Claim 2 in which the gripping means are in the form of a toothed ring. A coupling according to Claim 3 in which a gripping ring is provided at each end of the coupling. A coupling according to Claims 3 or 4 in which the gripping ring is frustoconical. A coupling according to any one of Claims 3 to 5 in which the gripping ring is an incomplete ring. A coupling according to any one of Claims 1 to 6 in which the inner casing and the outer casing both have longitudinal gaps, the gap in the inner casing being offset circumferentially from the gap in the outer casing so that the sealing sleeve is 15 2. 20 3 . 25 4. 30 5. 6. 7. 35 250 931 - 15 - supported around its entire periphery either by the inner casing or by the outer casing or by both casings. 5 8. A coupling according to any one of Claims 1 to 7 in which the sealing sleeve is provided with end seals which form seals between the flanges and the pipe ends. • 10 9. A coupling according to Claim 8 in which the end seal/»".are axial extensions of the sealing sleeve which are trapped between the flanges and the pipe. Jt- 10. A coupling according to any one of the preceding claims 15 in which the sleeve includes two sets of annular inwardly projecting sealing ribs on the inner surface of the sleeve which engage the respective pipe ends in a fluid-tight manner, the sealing ribs being of substantially square profile, one rib of 20 each set being located so as in use to be near the end of the corresponding pipe whereby the length of the sealing sleeve that is exposed to the hydrostatic pressure in the pipes is small compared with the overall length of the sealing sleeve. 25 30 11. A coupling according to Claim 10 including a central annular inwardly projecting sealing land „ which in use overlaps the ends of the pipes and ^ 7^]£?5 forms a seal against their outer surfaces. 12. A pipe coupling according to Claim 1 and substantially as hereinbefore described with reference to the accompanying drawings. 14 n,-: !authorised agents A J PARK & SON Per ■ \f V\ C\ a a i