US3012546A

US3012546A - Hydraulic props, particularly pit props

Info

Publication number: US3012546A
Application number: US811827A
Authority: US
Inventors: Heintzmann Hans Friedrich; Selz Rudolf; Blenkle Erwin; Lerbs Hellmut
Original assignee: Phoenix Gummiwerke AG
Current assignee: Phoenix AG
Priority date: 1958-05-10
Filing date: 1959-05-08
Publication date: 1961-12-12
Anticipated expiration: 1978-12-12
Also published as: FR1226787A

Description

Dec. 12, 1961 H. F. HEINTZMANN ET Al.

HYDRAULIC PROPS, PARTICULARLY PIT PROPS Filed May 8, 1959 4 Sheets-Sheet 1 mum/rags, 44W MM H W 3- Wk I Dec. 12, 1961 H. F. HEINTZMANN ETAI.

HYDRAULIC PROPS, PARTICULARLY PIT PROPS Filed May 8, 1959 4 Sheets-Sheet 2 M W 5.2mm!

OAT -M;

Dec. 12, 1961 H. F. HEINTZMANN ETAL 3,012,545

HYDRAULIC PROPS, PARTICULARLY PIT PROPS Filed May 8, 1959 4 Sheets-Sheet 3 PIC-i5 i llll Dec. 12, 1961 H. F. HEINTZMANN ETAL HYDRAULIC PROPS, PARTICULARLY PIT PROPS 4 Sheets-Sheet 4 Filed May 8, 1959 FIG. 6

IN VENfO/Pg H MW 1M Rum a Unite 3,012,546 HYDRAULIC PROPS, PARTICULARLY PH PROPS Hans Friedrich Heintzmaun, Rudolf Seiz, and Erwin Blenlile, Bochum, and Hellmut Lerhs, Hamburg-Langenhorn, Germany, assignors to Bochumer Gesellschaft fiir Grubenaushau u. Technik m.b.H., Bochum, Germany, and Phoenix Gummiwerlre Aktiengesellschnft, Hamburg-Harburg, Germany Filed May 8, 1959, Scr. No. 811,827 Claims priority, application Austria May 10, 1958 14 Ciaims. (Cl. Ell-46) There are hydraulic props, and particularly pit props, having an inner prop member which is guided for axial displacement in an outer prop member, constituting a compression chamber, with a sealing means arranged between them. Further hydraulically-operating supporting devices and constructional apparatus comprising a plurality of props, for example pillars, frames and walls, are known.

Water or oil, or a water-oil emulsion, are in these various instances, used as hydraulic media. The admission and discharge of the hydraulic medium may, for example in a mining installation, be performed from a supply container common to a plurality of props and through connecting conduits disposed in a gallery, these conduits being connected to couplings which are, for example, provided on the outer prop member. It is also possible, however, to effect the admission and discharge of the pressure medium through the inner prop member. It is possible, moreover, that a separate supply container is associated with each prop, this for example being disposed inside the inner prop member, and the pressure medium is supplied from this container to the compression chamber formed by the outer prop member, during the extension of the prop parts, i.e. during the bracing of the prop between the roof and the floor.

In these known hydraulic props or supports, difficulty is met in effecting the sealing between the telescopically interengaged prop parts. In known forms of construction the sealing is almost exclusively carried out between the surfaces which are movable relatively to one another, and more particularly between a piston which is provided at the inner end of the inner prop member and the inner wall of the compression chamber of the outer prop member.

To ensure adequate sealing, the sealing means must be fitted absolutely tight at these parts. The result of this, however, is that when the prop is relieved of pressure, i.e. when an exhaust valve associated with the compression chamber is opened, the inner prop is not inherently capable of sliding within the outer prop member on account of the large frictional resistance set up by the inner member, and an additional application and expenditure of eifort and work is required for this purpose.

Fabrication of these known props is comparatively costly because the sealing surfaces require accurate machining. Moreover, the walls of the inner and outer prop members which constitute the sealing surfaces are exposed to considerable danger of corrosion and rusting, particularly when water is used as the pressure medium and, in view of the unavoidable mechanical stresses and strains applied to the prop parts in mining operations deformation and/or superficial damage of the sealing walls of the prop readily occurs, and this may have the result that the coupling between the inner and outer prop members becomes imperfectly sealed, and/or there may be jamming of the two telescopic prop members.

Such hydraulic props, support, pillars, frames, walls, or supporting structures made up of pit props, of the kind referred to are generally referred to hereinafter as props,

' tion, by the fact that the inner prop member and the p and are improved, in accordance with the present invenouter prop member surrounding the same are interconnected by a fluidtight'bellows of flexible, for example resiliently deformable, material, which is guided for inversion and is adapted to perform a voluting movement on the inner and outer prop members during relative movement of these members. I

As a result, the connection between the two prop members is independent of any intersliding sealing surfaces, and consequently the frictional forces which are developed during the relative shifting of the prop members is reduced to a small proportion of the figure which is met with in known prop constructions. Since there is no direct sealing between the telescoping prop walls, it is possible to allow considerably greater manufacturing tolerances than in known constructions. Moreover, any corrosion and/or deformation of the prop walls is precluded from impairing the sealing of the prop members in any way whatsoever.

Advantageously the end sections of the volute bellows are firmly clamped to the inner and outer prop members, and it is generally found advisable to arrange for the clamping to take place at the outer wall of the inner prop member and the inner wall of the outer prop membet.

The volute bellows, firmly clamped atits ends and effecting the required sealing, rolls on the confronting surfaces of the inner and outer structural parts, i.e. the inner and outer prop members, rolling off one simultaneously with its being rolled out over the other, i.e. being both inverted and performing a volute movement. For this purpose only a small, and preferably resilient, deformation of the material of the bellows is required, and a correspondingly small expenditure of effort.

By virtue of the volute bellows which connects the two prop members in fiuidtight fashion, the part of the prop or support disposed outside the compression chambet is protected very effectively against corrosion. Furthermore, and particularly when water is used as the pres-. sure fluid, the prop surfaces which are directly exposed to the pressure fluid can very easily be given a corrosionresisting protective coating, since these surfaces no long er have to fulfill the function of sealing surfaces, in which case they would require very special and careful treatment.

The tluidtight volute bellows is advantageously made of a suitable resilient material, for example being of natural or artificial rubber, one of the various kinds of plastics, or mixtures thereof, and is provided with fabric inlays.

It is primarily of a construction such that the requisite rolling movements, and the consequent variations in the diameter of the bellows can be implemented without any difliculty. The bellows does not require to be expansible in its longitudinal direction, or only to a small extent. The degree of variation of the bellows diameter which is required during the volute movement is kept as small as possible. 'It is not necessary for the bellows to conform exactly to the dimensions of the inner and outer prop members since the wall surfaces of the bellows facing the inner and outer prop members are applied by the pressure of the pressure fluid against these confronting walls.

In an advantageous embodiment, the clamping to the Advantageously a guide plate is attached to the inner j I end of the inner prop member, this being provided with perforations or peripheral recesses for connecting the parts of the compression chamber, arranged at the two sides of the guide plate, for fluidflow between them. In this event, the end section of the volute bellows adjacent the inner prop member can be clamped between this guide plate and the end of the inner prop member.

In an advantageous arrangement the outer prop member comprises two cylindrical sections which are divided along a plane extending substantially at right angles to the axis of the prop, and the end section of the volute bellows adjacent the outer prop member is gripped between these cylindrical sections.

It is particularly advantageous in such an arrangement, for the two cylindrical sections of the outer prop member to be detachably coupled together by a coupling ring which encloses the adjacent ends of said cylindrical sections in sleeve fashion externally and/ or internally. This enables the use of cylindrical sections for the outer prop member which are of the same diameter at their adjacent ends. Use may therefore be made of sections of tube which are to be come by in the trade without, for example, one end of the cylindrical section having to be enlarged and/or machined for the insertion or screwing in of the other cylindrical section. At the same time, any reduction in wall thickness and in variation of the tensile strength in relation to the untouched part of the length of the cylindrical section is avoided. The use of cylindrical or tubular sections which are readily available in the trade also reduces the Overheads and costs of manufacture, without harming the etficiency of the prop.

in accordance with a further feature of the invention, the coupling ring has a sealing flange which projects inwards in a substantially radial direction and against which the adjacent ends of the two cylindrical sections seal. From this it will be immediately apparent that the sealing of the high pressure prop and the fluid therein is greatly simplified and improved, since the sealing is not only performed by the annular surfaces of the coupling ring which bear against the outer and inner peripheries of the cylindrical sections of the prop, but also at the end faces of the sealing flange.

A further improvement is secured by making the sealing flange of substantial thickness in the longitudinal direction of the prop and housing in this flange all the valves associated with the compression chamber of the prop. This has the advantage that the valves are at a part of the prop, substantially in fact at about half the height of the latter, outside the zone of movement of the inner prop piston, so that these valves can be arranged entirely within the prop without interfering with the longitudinal shifting of the prop members. Apart from the fact that this guards the valves against damage (which is a very desirable condition in undergroundmining), this positioning of the valves has the attribute that they are readily accessible for maintenance, when the prop is appropriately disposed, and are exposed only to a very small degree to the liability of contamination or damage by coal, stone or rubble.

Generally speaking it is advantageous to arrange the valves in the same cross-sectional plane of the sealing flange offset from one another in the peripheral direction, and such that the longitudinal axes thereof are radial in relation to the axis of the prop. As a result the width of the coupling ring, measured in the longitudinal direction of the prop, and the thickness of the sealing flange, can be comparatively small.

To prevent soiling of the valves, in accordance with a further feature of the invention the outwardly-directed connecting ports of the valves are adapted to be closed against the ingress of dust. This can be effected by pro viding for closure of the connecting ports by one or more guard caps which is or are movably mounted on the coupling ring. Thus, for example, a guard cap having openings corresponding in positions and diameter to the ports of the valves can be mounted on the coupling ring so as to be movable thereon for the purpose of opening or closing the valve ports. For this purpose the guard cap can be mounted on the coupling ring merely for rotary movement, or can be displaceable in the longitudinal direction of the prop. Additionally it is possible to rotatably couple the guard cap with the coupling ring by means of screw threading which is pitched in the longitudinal direction of the prop. It can be arranged that when the guard cap is moved, either all the valve ports are opened or closed simultaneously, or only certain of them at appropriate times. Furthermore a projection can be provided on the guard cap to serve as a bearing for a lever for opening the pressure relief valve.

The outer diameter of the inner prop member is advantageously made only a little smaller than the inner diameter of the sealing flange of the coupling ring which projects into the annular space between the outer prop member and the inner prop member. The virtue of this arrangement is that the flow of the pressure fluid, and the volute movement of the bellows clamped at its ends to the outer and inner prop members, are not obstructed dur ing the setting or collapsing of the prop. The outer margin of the volute bellows is advantageously then clamped between the sealing flange of the coupling ring and the confronting end of the inner cylindrical section of the outer prop member.

In accordance with a further feature of the invention, the marginal sections of the bellows clamped at the outer and inner prop members are of greater tensile strength than the remainder of the length of the bellows. This confers a greater resistance to the marginal sections of the bellows which are, naturally, exposed to heavier loads and stresses due to their clamping to the prop members, and this increased resistance ensures a proper sealing of the compression chamber of the prop and an eflicient operation and life for the bellows.

To provide for this increased tensile strength relatively to the parts of the length of the bellows disposed between its ends, it is found advantageous to reinforce the marginal sections of the bellows by beading. The stiffness hereby produced prevents the buckling in of the bellows at the ends under the effect of the fluid pressure which prevails when the prop is loaded, whereby the marginal sections can advantageously support the stresses which are required for sealing but nevertheless exhibit a degree of flexibility such as is required to allow the volute bellows to be laid into the prop, i.e. for a proper operation of the bellows.

The marginal sections of the volute bellows provided with beading reinforcements may, in appropriate cases, be equipped with spaced sealing lips, the gaps between which provide for a stagewise sealing of the compression chamber.

The stiffness of the marginal sections of the volute bellows may be further improved by providing the marginal beads with reinforcing inserts of materials of a greater tensile strength than that of the remainder of the bellows. These reinforcing inserts are advantageously in the form of stiffening rings which are embedded in the beads. The rings may, for example, be comprised of wire braid, wire cord or the like and are advantageously prepared so as to provide for an effective bonding between the same and the material of the bellows, which, for example, is an elastomeric material such as natural or artificial rubber, plastics of various kinds, or mixtures of these. The stiffness of the marginal sections of the volute bellows is so substantially increased in this way as to practically preclude any danger of buckling in of the margins.

Because the marginal sections of volute bellows is exposed to very powerful stresses and strains, it is advisable to provide the bellows with fabric inlays, at any rate in the marginal zones thereof. In addition the tensile strength of the bellows is considerably increased by this means. Advantageously the fabric inlays are composed of at least two superimposed corded layers embedded in the resilient material of the bellows. The corded fabric may be directly exposed to high tensile strains and primarily fulfils the function of sustaining the tensile stresses which are developed in the bellows, and in view of the small thickness of the fabric the bellows may be of smaller wall thickness. Asa consequence of this, moreover, when the bellows rolls on and off between the inner and outer prop members, only a small resistance to bending occurs and this promotes a substaintially extended length of useful life for the bellows.

The reduced wall thickness of the bellows, allowed for by using the corded fabric, enables the radial distance between the inner and outer prop members to be kept comparatively small. in consequence of this a volute bellows of this nature can sustain relatively high specific surface pressures. In this connection a further improvement is achieved by crossing the cord lengths at an angle of about l040 and disposing them substantially symmetrically in relation to the longitudinal axis of the prop. Apart from the fact that the crossed arrangement of the fabric webs promotes an unopposed volute movement of the bellows during the operation of the prop, a bellows reinforced in this way is notable because of the limited expansibilit-y which it possesses, but at the same time its capacity to sustain very high tensile strains. In addition, a crossover system of fabric webs very effectively opposes twisting forces acting on the bellows.

The capacity of the bellows to sustain powerful tensile strains can be further increased by disposing the fabric inlays in sleeve fashion around the reinforcing rings. By this means the portion of the volute bellows between its marginal sections is suspended by the fabric webs to some extent on the reinforcing rings in the marginal beads of the bellows so that the forces which are more particularly effective at the clamped marginal beads are transmitted through the fabric to the remainder of the bellows. At the same time the fabric wrapping around the reinforcing rings increases the cross-sectional size of the beaded margin, thereby increasing the sealing properties. In addition the elasticity of the marginal beads is increased and the danger avoided that the resilient material of the bellows disposed above the reinforcing rings will be crushed and damaged under the action of the clamping forces.

A further feature of the invention resides in gripping the volute bellows in sealed fashion, directly alongside the marginal beads, between two clamping surfaces provided on the outer or the inner prop member, as the case may be. Advantageously the clamping surfaces are associated with sealing surfaces which are applied against the marginal bead, whereby these beads are drawn, under the fluid pressure prevailing in the compression chamber of the prop, against the sealing surfaces of the clamping surfaces, and in the event of a high internal pressure in the prop, are pressed under correspondingly high pressures against the sealing surfaces so as to effect complete sealing.

Advantageously the associated clamping surfaces are enlarged towards the marginal bead of the volute bellows to form an annular chamber which is of a crosssection which is only of slightly larger area than the beaded and reinforced margin of the volute bellows. As a result of this the marginal beads are exposed substantially only to the tensile strains'which act on the bellows when the prop is under load, and are mounted freely in the annular chambers, depending on the size of these forces and their elasticity; Since, as a-result, the parts of the bellows located in the vicinity of the heading are not subject at all, or only to an insignificant extent, to deformation, the anchorage and overlapping of the fabric webs is safeguarded.

In this arrangement it is of advantage to associate with the clamping surfaces centering and make-up surfaces which determine the minimum distance between the 6. clamping surfaces. This can avoid damage occurring as a result of an excessively powerful gripping of the marginal sections of the bellows. between the clamping surfaces can be made dependent on the elastic properties of the material selected for the bellows so that, in every case, the pre-tensioning efforts which are required for the clamping ensure, on the one hand, proper sealing and, on the other hand, ample conservation of the bellows material.

A further feature of the invention resides in the fact that the clamping surfaces associated with the outer prop member are effective in the cross-sectional area of the outer prop wall and substantially parallel to the prop axis. Advantageously the clamping surfaces of the outer prop member are formed by the opposed ends of a clamping jaw and a coupling ring which is detachably fastened to the outer cylindrical section of the outer prop member and is adapted to be clamped in the axial direction to the clamping jaw by a clamping ring. The clamping ring is freely rotatable on the clamping jaw of the inner cylindrical section but is mounted for axial displacement towards the outer cylindrical section of the outer prop member and is connected to the coupling ring by means of threading which is pitched in the axial direction.

This anchoring together of the two cylindrical sections of the outer prop member, which are preferably split in a plane at right angles to the axis of the prop, reduces bending moments to a minimum, whilst at the same time favorising the system of forces developed in the prop as a result of the loading thereof. In addition the radial extent of the clamping surfaces, like the length of the volute bellows, can be kept relatively small. The clamp ing ring not only allows for clamping of the outer margin of the bellows, but at the same time for the centeringthe annular gap between the inner and outer prop memhers is of a size as indicated, without being subject to damaging bending strains. A small radial spacing between the inner and outer prop members additionally means that the outer prop member need not generally be of larger diameter than conventional props which are not equipped with volute bellows.

It is also advantageous to telescope the outer and inner prop members in such a way that only a small relative rotation is possible between these two prop members during the telescopic movement. This makes the prop more efficient in operation and safeguards the bellows.

In one specific form, only the outer portion of the inner prop member is cylindrical, whilst the inner end of the inner prop member is formed by a guide plate which is connected to the cylindrical portion and is spaced from the latter, this guide plate being provided with perforations and being guided on the inner wall of the outer prop member. This substantially reduces the overall weight of the prop without any impairing of the efiiciency or convenience in installation. The pressure fluid in the prop can flow to and from the compressionchamber through the perforations in the guide plate, depending on the particular load conditions at any time. The guide plate on the inner prop member has the addi-. tional function that, like the coupling ring of the outer propmember, it constitutes one of the abutments determining the fully extended length of the prop.

Advantageously the guide plate is detachably fastened The size of the gap to a threaded bolt which projects coaxially in relation to the prop axis into the compression chamber, the other end of this bolt being firmly, but detachably, connected to a plate for closing the cylindrical portion of the inner prop member, and a clamping plate, through which passes the threaded bolt, is adapted to be clamped against the closure plate by means of a nut screwed on to the threaded bolt.

Conveniently the end of the cylindrical portion of the inner prop member is sealed by the closure plate, which conforms with the outer diameter of this inner prop member, and the side of this closure plate nearest the compression chamber of the prop forms with the opposed side of the clamping plate an annular chamber for accommodating a marginal head of the volute bellows. This secures the same advantages as does the annular chamber which is provided in the outer prop member.

To enable the volute bellows to be applied with as little resistance as possible from the clamping position on the inner prop member to the outer surface of this member, it is advantageous to give the clamping surfaces on the closure plate a larger radius of curvature than the clamping surfaces on the clamping plate. As a result the clamping surfaces of the clamping plate press the volute bellows more or less in the direction of the superfices of the inner prop member, and this bellows is therefore applied fully against the surface of this member.

In a further and advantageous embodiment of the invention, at least one further volute bellows is associated with the first-mentioned volute bellows, and the two bellows are coaxially nested and are in direct contact at least at the parts of their lengths adjacent the prop members. This increases the load capacity of the prop, and consequently its safety in operation and its length of life, very considerably, since each of the volute bellows has only to take a part of the total load.

The marginal sections of the volute bellows adjacent the prop members (outer and/or inner prop members) may be clamped in sealed fashion in a common crosssectional plane of the prop or, in accordance with a further feature of the invention, in different cross-sectional planes of the prop which are axially spaced from one another.

In an advantageous further arrangement, the volute bellows are continuously applied directly against one another over substantially their full lengths, and the outer volute bellows, which is adjacent the compression chamber of the prop and bears directly against the inner peripheral surface of the outer prop member and the outer peripheral surface of the inner prop member, is of greater tensile strength than the inner volute bellows.

For the purpose of sustaining the pressure corresponding to a maximum loading of the prop, the outer volute bellows may be made of a material of high tensile strength whilst the inner volute bellows is of a material which is adapted to seal the compression chamber of the prop. Since a larger radius of curvature is available for the outer volute bellows at the roll-over zone between the outer and inner prop members, than is available for the inner volute bellows, this outer bellows can be of a harder and more robust, i.e. less flexible, material than the other bellows.

To avoid wear as a result of friction between the individual volute bellows, and at the same time to ensure a uniform transmission of the pressure effective in the compression chamber of the prop to the outer volute bellows, it is advantageous for the longitudinal sections of the volute bellows of fluidtight material arranged in the vicinity of the volute part of the bellows between the outer and inner prop members to be spaced from one another in the longitudinal direction of prop and to enclose an annular chamber for receiving a fluid pressure transmitting medium which is chemically neutral in relation to the material of the bellows.

Conveniently an admission conduit leading to the annular chamber accommodating the pressure transmitting medium is provided between the volute bellows in the vicinity of the position at which the marginal sections of the volute bellows are connected to the outer prop member. The relative movement between the outer and inner prop members is facilitated by the pressure transmitting medium, which is advantageously incompressible and at the same time performs a lubricating function, and sticking together of the two volute bellows is avoided, even under maximum load.

A number of embodiments of the invention are illustrated by way of example in the accompanying drawings in relation to pit props which are intended for use in underground mining.

In these drawings:

FIGURE 1 illustrates a first prop in longitudinal section;

FIGURE 2 is a cross section on the line IIII of FIGURE 1;

FIGURE 3 is a longitudinal section through a second embodiment of pit prop;

FIGURE 4 is a cross section on the line IV-IV of FIGURE 3;

FIGURE 5 is likewise a longitudinal section, in this case through a third embodiment;

FIGURE 6 is a longitudinal section through a fourth embodiment of the prop according to this invention.

In all the embodiments illustrated, the hydraulic pit prop, which is more particularly intended for mining, comprises an inner prop member 1, which is here a lower prop member, and an outer and upper prop member 2. The outer and inner prop members are coupled together in fiuidtight fashion by at least one volute bellows 3. The inner margin of the bellows 3 is tightly and firmly clamped to the outer periphery of the inner prop member 1, and the outer margin of the bellows to the inner periphery of outer prop member 2.

The outer member 2 comprises an inner cylindrical section 2a and an outer cylindrical section 2b, and in the embodiments illustrated in FIGURES I to 4, these two

cylindrical sections

2a, 2b are connected by a coupling ring 4 which forms a sleeve surrounding the adjacent ends of the

sections

2a, 2b at the exterior and is detachably connected to these ends, e.g. by screw threading 5. In contrast to the constructions illustrated in FIGURES 1 to 4, the coupling ring can, of course, in appropriate cases, additionally surround the ends of the

cylindrical sections

2a, 2b at the inside in sleeve fashion.

In all the embodiments illustrated in the drawings, the inner cylindrical section 2a is of substantially shorter length than the outer section 2b, whilst both cylindrical sections are of the same internal and external diameters. It will be understood, however, that the diameter of the

cylindrical sections

2a and 2b may be different, or the ratio of their lengths may be other than that chosen in this particular case.

As can be seen from FIGURES 1 to 4, the coupling ring 4 has a sealing flange 4a which projects radially inwards and against which the adjoining ends of the two

cylindrical sections

2a, 2b are sealed, with an interposed packing 6 for the outer cylindrical section 2b and a sealing ring 7 for the inner section 2a. The outer margin 3a of the volute bellows 3 is gripped between the sealing flange 4a of the coupling ring 4 and the end of the inner cylindrical section 2a of the outer prop member 2 opposed to this coupling ring, with a sealing ring 7 disposed between them. As can be observed from FIGURES 1 and 3, the outer diameter of the inner prop member is less than the inner diameter of the sealing flange 4a which projects into the annular space 8 between the outer prop member 2 and the inner prop member 1, but only by an amount corresponding to about four times the wall thickness of the bellows 3.

In the embodiment illustrated in FIGURES 1 and 2, the

sealing flange 4a of the coupling ring 4 is of a substantial thickness in the longitudinal direction of the prop and one which exceeds its radial width by a small amount. The sealing flange 4 houses an excess pressure valve 9 and a valve 10 disposed diametrically opposite it in the same cross-sectional plane, this latter valve, which is of the non-return type, being connected to a pressure medium supply conduit, and being at the same time adapted for use as a pressure relief valve.

It is, of course, possible to arrange more than two valves, offset from one another in the peripheral direction, in the sealing flange 4a of the coupling ring 4, for instance a non-return valve, an excess pressure valve, and a separate pressure relief valve. The length of each of the valve housings 9a, 10:: is approximately equal to the difference between the inner and outer diameters of the coupling ring 4, so that the inner and outer surfaces of the coupling ring lie flush with the opposite ends of the valve housings 9a, 10a. This affords a minimum radial width for the coupling ring 4.

To provide for a dust-sealed closure of the

outer valve openings

9b, 1% of the

respective valves

9, 10, a guard cap 11 is arranged on the coupling ring 4, this cap surrounding the part of the coupling ring 4 covering the

cylindrical sections

2a, 2b and being rotatably mounted on this ring. The guard cap is provided with openings 11a, 11b which are in positions, and of a diameter, corresponding to the valve openings 91;, 16b. Consequently the openings 11a, 11b are located in the same cross-sectional plane as the valve openings 9b, 10b, but are offset diametrically by 180 one relatively to the other. Thus a manual rotary movement of the guard cap 11 can close or open both the valve opening of the non-return valve 9 and also that of the pressure relief valve 10.

It will also be understood that it is possible, instead of having a rotatable mounting of the guard cap 11, to mount this so that it will slide on the coupling ring 4 exclusively in the longitudinal direction of the prop, in which event detent means or the like may be provided for adjusting or locking the position of the cap. Again, under certain conditions, the guard cap can be mounted for rotation on the coupling ring 4 by means of screw threading.

A projection 12, fastened to the guard cap 11 in the vicinity of the opening 11b associated with the pressure relief valve 10, serves as a bearing for a removable lever 13 for opening the pressure relief valve 10. For this purpose, the lever 13 is in the form of a hinged lever whose shorter lever arm can be pushed into the valve opening 10b of the pressure relief valve 10. When this occurs, the valve body is lifted from its seat against the pressure of a closure spring, so that compressed fluid can pass into the annular chamber 8 and, through a connecting fluid conduit, to the compression chamber 8a.

The annular chamber 8 and the compression chamber 8a are separated by a guide plate 14 which is provided at the periphery with recesses 14a of large cross section to allow for a reciprocal flow of the pressure fluid between the compression chamber 8:: and the annular chamber 8. The guide plate 14 is secured to the inner end of the inner prop member by means of a bolt 15 which is threaded so as to engage with a tapped bore in the bottom plate It; of the inner prop member 1, which bore is coaxial with the prop.

The inner margin 3b of the volute bellows 3, which advantageously can be of beaded, reinforced construction, as can also the outer margin 3a, is gripped between the end surface of the inner prop member 1, which is constituted by a section of tube, and a recess 14b in the guide plate 14 in the form of an annular groove.

As can be seen from the drawing, the clamping efforts direction of the superfices of a cylinder of a diameter equal to the mean diameter of the outer prop member 2 and the inner prop member 1.

When the telescopic prop parts are extended, the bellows 3 rolls off the inner prop member 1 and a corresponding length of this bellows is applied against the inner face of the outer prop member 2. When the prop parts are telescoped in the opposite direction, contrarywise a part of the bellows 3 lifts off the inner wall of the outer prop member 1 and is rolled over and applied against the outer face of the inner prop member 2, wherefore it has been termed a volute bellows.

The inner margin 31) of the volute bellows may, in contrast to the arrangements illustrated in FIGURES l to 4, be clamped or fastened to the inner prop member 1 at a considerable distance from the guide plate 14, and this allows for the use of a bellows 3 of a comparatively small axial length. The arrangement of the clamping zone at the inner end of the inner prop member 1 has, however, the advantage that the inner member is then undivided and exposed over its full length to the direct action of the pressure fluid. The part at which the outer margin 3a of the bellows 3 is clamped can, in contrast to the embodiments illustrated in the drawing, alternatively be provided directly in the vicinity of the head plate 17 of the outer prop member 1 so that the guide plate 14 slides over the inside of the bellows. In this event the outer prop member 2 will be enveloped over its complete length by the bellows 3.

In the embodiment illustrated in FIGURES 3 and 4,

the head plate 17 accommodates an inlet valve 18 in the form of a spring-loaded non-return valve, and a further valve 19 which serves both as an excess pressure valve and a manually operable pressure relief valve.

Valves

18 and 1? communicate with the compression chamber 3a of the outer prop member 2 through channels 20.

In the embodiments illustrated in the drawings, the inner prop member 1 serves as the lower prop member, and the outer member 2 as the upper prop member. This arrangement has the advantage that there is no need for any special or careful caulking between the inner mem her 1 and a cap 21 which closes the outer prop member 2 at its inner end. No contaminating bodies can be deposited at this part nor can any damage occur here from fracturing stone. This arrangement conforms with the basic principle of the invention, which is that only very minor sealing means, or if possible none at all, which are provided by surfaces which slide relatively on one another, are used. The arrangement of the prop illus trated in the drawings is not, however, essential to the operation of the bellows 3 provided in the prop, and the latter can therefore be inverted through without any undue diificulty so that the inner prop member 1 represents the upper prop and the member 2 the lower prop member bears against the ground.

It is also possible to combine a plurality of props of the forms described above to form pillars, and fluid conduits may be so connected between the compression chambers of the various props as to allow for balancing the loading of the props. parts of a supporting member of a very large diameter so as to produce a supporting pillar in the form of a single prop.

The marginal sections 3a, 3b of the bellows 3 which are fastened to the outer and

inner prop members

2 and 1 respectively are to be of greater tensile strength than the remainder of the bellows and, for this purpose, are thickened or beaded. The marginal beads of the bellows 3, which may be made of an elastomeric material, for example of natural or artificial rubber or of plastic with rubber-like properties, are provided with rein-forcing inserts of material which is of greater tensile strength than the bellows 3 itself.

These reinforcing inserts may, for example, be constb tuted by stiffening

rings

22, 23 which are embedded in the marginal beads 3a, 3b and advantageously comprise It is also feasible to make the wire, cord, braid or the like. The stiffening rings 22, 23 advantageously are treated, so as to be capable of firm bonding to the elastic material of the bellows 3, prior to being incorporated in the marginal sections. In addition, the bellows 3 is provided, at least in the vicinity of its marginal sections 3a, 3b, with woven inserts consisting of at least two corded layers which are arranged one above the other and are embedded in the elastic material of the bellows. These corded fabrics (which have not been illustrated in the drawings) are advantageously crossed at an angle of about to 40 and are arranged substantially symmetrically in relation to the longitudinal axis of the prop, the reinforcing

rings

22, 23 being surrounded sleevewise by the fabric inlays.

The volute bellows 3 is made of a length advantageously somewhat more than half of the length of the full stroke of the prop so that, when the prop is in its unstressed condition, the bellows is relieved of stress, and where the prop is set the bellows is stressed exclusively by the fluid pressure prevailing in the compression chamber 8a and in the annular chamber 8.

It will be understood that material other than woven cord can be used as the inlays of high tensile strength. Thus, for example, fabrics of metal or plastic materials can be used in appropriate circumstances, so long as they fulfill the condition that they are of high tensile strength allied with a limited capacity for expansion.

In the embodiment illustrated in FIGURE 5, the marginal head 3a of the bellows 3 is arranged in an annular chamber 24 in the outer prop member 2, which chamber is of larger diameter than the outside diameter of the prop member 2 and whose cross-section is slightly more than that of the marginal bead 3a. One half of the annular chamber 24 accommodating the outer marginal bead 3a is defined in a coupling ring 25, and the other half by a clamping jaw 26, the coupling ring 25 being connected to the outer cylindrical section 2b of the outer prop memher 2, with an interposed packing 27, by means of threading 28. On the other hand, the clamping jaw 26 is welded to the inner cylindrical section 2a of the outer prop member 2, and is thereby sealed. The opposed end surfaces of the coupling ring 25 and the clamping jaw 26, defining the annular chamber 24, are formed in the vicinity of the outwardly-directed peripheral portion of the annular chamber 24 as centering and make-up surfaces 25a and 26a respectively, these parts serving to centre the

cylindrical sections

2a, 2b of the outer prop member, which are split in a plane substantially at right angles to the prop axis, and to apply them firmly one against the other in the axial direction.

The clamping surfaces 25b, 26b, of the coupling ring 25 and the clamping jaw 26, which are flared outwardly to the annular chamber 24, are spaced by an amount determined by the mutually seating surfaces 250 and 26a and serve for the sealed gripping and fastening of the bellows 3 directly adjacent the outer annular marginal bead 3a, for which purpose the clamping surfaces 25b, 2611 are provided with sealing surfaces which bear against the bead.

The clamping faces 25b, 26b of the coupling ring 25 and the clamping jaw 26 associated with the outer prop member 2 are effective in the region of the outer prop wall and substantially parallel to the prop axis. The clamping surfaces 25b, 2612, which are rounded, merge progressively into the cylindrical inner surface of the coupling ring 25 and the clamping jaw 26 respectively, and the diameter of these parts is substantially that of the inner diameter of the outer prop member 2.

To develop the tightening effort which is required to clamp the annular bead 3a of the bellows 3 and to connect the two

cylindrical sections

2a, 2b of the outer prop member 2, use is made of a clamping ring 29 which is freely rotatable on the clamping jaw 26, but is mounted so as to be axially immovable towards the outer cylindrical section 212 of the outer member 2, and is connected to the coupling ring 25 by means of threading which is pitched in the axial direction.

The coupling ring 25 has an annular flange 25c which is directed radially inwardly and has both the compression chamber 8a and the annular chamber 8 of the prop, connected to chamber 8a, both arranged therein. FIG- URE 5 only shows the spring-loaded excess pressure valve 30 and this has a valve housing of a length substantially equal to the radial width of the flange 250. The inlet valve for the pressure fluid, which is in the form of a nonreturn valve, and the manually operable pressure relief valve, which are also arranged in the annular flange 25c of the coupling ring 25, are not shown in FIGURE 5.

The annular flange 250 has an inner diameter which corresponds substantially to the mean diameter of the annular chamber 8. As a result it is, of course possible to make the inner surface of the coupling ring 25 flush with the inner wall of the outer prop member 2. On the other hand it may, in other instances, be more advantageous to so provide the coupling ring 25 that the end of the outer cylindrical section 2b encloses this ring in sleeve fashion not only externally, but internally as well.

FIGURE 5 shows that the annular chamber 8 is made larger than the outer radius of the inner prop member 1 by an amount which is approximately four times the wall thickness of the bellows 3. The inner prop member 1, and the outer prop member 2 are guided, one in the other (by means not shown) so that only a small relative rotation is possible between these two members.

The inner marginal bead 3b of the bellows 3 is made of smaller diameter than the outer diameter of the cylindrical part 1a of the inner prop member 1. The annular bead 3b is mounted in an annular chamber 31 at the inner end of the cylindrical part 1a which is of a crosssection also larger than the cross-section of the annular bead 3b.

The bellows 3 is provided externally, and in the vicinity of the inner annular bead 3b, with circular sealing lips 3c which are accommodated in a sealing surface 32c, which is recessed in annular groove fashion, of a clamping plate 32. The plane of the annular sealing surface 32c is approximately at right angles to the longitudinal axis of the prop, and this surface is of greater radial width than the annular chamber 31.

The sealing surface 32c of the clamping plate 32 is bounded externally by a rounded rim which projects towards the inner prop member 1 and forms a clamping surface 32b which presses the part of the length of the bellows 3 directly adjacent the marginal bead 3b against the clamping surface 33b of a closure plate 33 of the inner prop member 1.

The clamping surface 33b of the closure plate 33 is turned inwards, through an angle of about 45 relatively to the prop axis, towards the compression chamber and constitutes the outer rim of an annular groove which is disposed below the same and forms the major part of the annular chamber 31. The clamping surface 331; provided on the closure plate 33 is of greater radius of curvature than the clamping surface 32/; on the clamping plate 32, whereby the bellows 3 is pressed towards the outer end of the inner prop member 1 and against the outer surface of the latter.

The opposed faces of the clamping plate 32 and the closure plate 33 of the inner prop member are provided with conforming centering and make-up surfaces 321: and 33a, by means of which the clamping plate 32 is centered on the closure plate 33 and is applied against the latter in the axial direction. At the same time, this interseating of the

surfaces

32a, 33a determines the distance between the clamping surfaces 32b and 33b of the clamping plate and closure plate, and this is so chosen, in accordance with the wall thickness of the bellows 3, that there is a reliable and effective clamping of the head 31) without damage to the bellows 3.

In the embodiment illustrated in FIGURE 5, with the object of securing a very short bellows 3 and at the same time a large relative shifting movement, the outer bead 3a is fastened approximately mid-way between the two end positions of the inner bead 3b.

The closure plate 33 is screwed into the shorter cylindrical part 111 of the inner prop member by threading 34. It is provided at the end with a threaded bolt 35 which projects in the direction of the prop axis into the annulus chamber 8, and a guide plate 36 is screwed on to the free end of this bolt at a substantial distance from the inner end of the cylindrical part 1a.

The guide plate 36 is provided with a plurality of perforations 36a of large diameter. The pressure fluid can flow through the perforations 26a, when the prop parts are extended, into the pressure chamber 8a located between the guide plate 36 and the head plate 17 of the outer prop member 2, and when the prop parts are telescoped together, it can flow back through these perforations into the annular chamber 8. The clamping plate 32 Slipped over the flanged bolt 35 is held by means of a nut 37 against the closure plate 33 and the marginal bead 3b of the bellows.

As can be seen from FIGURE 5, the guide plate 36 of the inner prop member 1 and the coupling ring 25 of the outer prop member 2 constitute abutments which define the extended length of the prop, whilst the telescopic zovement of the prop parts is limited by the abutment of the guide plate 36 of the inner prop member 1 against the head plate 17 of the outer prop member 2.

In the embodiment illustrated in FIGURE 6, the volute bellows connecting the inner and outer prop members has associated therewith at least one further volute bellows 33, these two

bellows

3 and 38 being nested coaxially in direct mutual contact, at least at the parts thereof adjacent the

prop members

1 and 2.

The

bellows

3, 38 are made of a fluidtight material, for example of elastomeric materials, that is to say of synthetic rubbers or rubber-like plastics. The sections 30, 380 of the

bellows

3, 38 located at the rolling zone between the outer and inner prop members areas seen in the longitudinal direction-spaced from one another and enclose an annular chamber 39 for receiving a pressure transmitting medium, for example water, which is chemically neutral in relation to the material of the bellows. The volume of the pressure transmitting medium, which also exerts something of a lubricating function between the bellows, is substantially smaller than the volume of the operating medium in the compression chamber 8a and the annular chamber '8 of the prop.

Generally speaking, it suffices if the axial distance between the longitudinal'sections 3c, 380 between the outer and inner prop members in the volute zone is substantially equal to the wall thickness of a single bellows. The annular chamber 39 is so constituted that the outer and inner

marginal sections

3a, 38a and 3b, 38b of the

bellows

3, 38 are gripped at two different cross-sectional planes in the prop. In the present instance the axial distance between the clamping planes at the outer prop member is greater than those which apply at the inner prop member, and the two bellows are of the same length. t will be understood that the annular chamber 39 can be so formed that the

bellows

3, 38 are of different lengths, presuming that the outer and inner marginal sections are gripped in a common plane.

When the prop is free of load, the pressure transmitting medium is charged into the annular chamber 39, preferably With the prop members in a relative position such that the

sections

30, 38c of the bellows in the zone of the voluting portions are at the level of a closable admission conduit 45) which is provided between the clamping zones of the outer

marginal sections

3a, 38a. In the normal operating condition, the admission conduit 4! is covered by the inner bellows 38.

Whilst in the embodiment illustrated in FIGURE 6 the

bellows

3, 38 are of the same elastomeric material and of the same wall thickness, and include a reinforcement of steel cording which may increase towards the centre and consequently sustain in each case about half the pressure prevailing in the compression chamber of the prop, it will be understood that the outer bellows 3, may be of greatertensile strength than the inner bellows 38. To this end, either the wall thickness of the outer bellows 3 can be increased, or it may be made of a stronger material.

If the use of a pressure transmitting medium between the

bellows

3, 38 is dispensed with, these bellows may be applied directly against one another over substantially their full lengths, in the event that the outer bellows 3 is, for the purpose of sustaining a pressure corresponding to the maximum prop loading, made of a material of high tensile strength, e.g. steel mesh or steel net, and the inner bellows is of a material, e.g. rubber, which is adapted to seal the compression chamber of the prop in fluidtight fashion.

In the embodiment illustrated in FIGURE 6, the marginal sections 31), 38b and 3a, 38a of the

bellows

3, 38, which are fastened to the inner and outer prop members respectively, are of greater tensile strength than the remainder of these bellows and for this purposehave a reinforcing beading. The marginal beading is provided with reinforcing inserts of a material which is of higher tensile strength than the material of the bellows.

In the embodiment illustrated in FIGURE 6, reinforcing

rings

22, 23 are embedded within the

marginal beads

3a, 38a and 3b, 381), and these may for example be of wire braid, wire cords or the like. Before being embedded, these reinforcing rings are advantageously prepared so that they will potentially bond very effectively to the resilient material of the

bellows

3, 38.

In addition, the

bellows

3, 38 may be provided, at any rate in the zones of their

marginal sections

3a, 3b and 38a, 38b, with fabric inlays consisting of at least two layers of cord arranged one above the other and embedded in the elastic material of the bellows. The cord layers, which are not shown in FIGURE 6, may advantageously be crossed at an angle of about 10 to 40, and substantially symetnically to the longitudinal axis of the prop, the reinforcing

rings

22, 23, being surrounded sleevewise by the woven inserts.

The

bellows

3, 38 are advantageously of a length equal to more than half the extending stroke of the prop, so that the bellows are relieved of load when the prop is in its collapsed condition, and are loaded exclusively by the fluid pressure prevailing in the compression chamber 8a, and the annular chamber 8, when the prop is set.

The gripping means for the outer annular beads 3a,

38a, which are arranged in axially spaced transverse planes, are constituted by the opposing end faces of a clamping jaw 41, which is secured to the inner cylindrical secti n 2a of the outer prop member 2, and a coupling ring 43 which is connected thereto by a clamping'ring 42 andis secured to the outer cylindrical section 2b of the outer prop member, and by at least one intermediate ring 44 which is provided between the coupling ring 43 and the clamping jaw 41. The opposed end faces of the clamping jaw 41, of the intermediate ring 44, and the coupling ring 43, in each case define an annular chamber to accommodate the

beads

3a, 38a of the two bellows, these annular chambers having a diameter which 'is larger than that of the outer prop member and a crosssectional area which is sli htly larger than that of the

annular beads

3a, 38a.

The end faces of the coupling ring 43, the intermediate ring 44, andthe clamping jaw 41, defining the annular chambers are in the form of make-up.

pieces

45, 46 in the vicinity of the outwardly directed peripheral part of the annular chambers, and these pieces determine the:

axial distance between the

cylindrical sections

2a, 2b.

at right angles to the axis of the prop.

The clamping surfaces of the coupling ring 43, the intermediate ring 44 and the clamping jaw 41 which are flared outwardly towards the annular chamber, and are directed towards one another in bead fashion, are arranged at a distance from one another determined by the seating of the

surfaces

45, 46, and serve to sealingly grip the

bellows

3, 38 directly alongside the

annular beads

3a, 38a.

The clamping surfaces, projecting in beaded fashion towards one another, for the outer marginal beads of the bellows are effective in the zone of the wall of the outer prop member 2, and substantially parallel to the axis of the prop. The clamping surfaces, which are rounded off at their ends, merge progressively into the inner surfaces of the coupling ring 43, the intermediate ring 44 and the clamping jaw 41, the diameter of which corresponds substantially to the inner diameter of the upper prop member 2.

The clamping ring 42 which extends over the annular ring 44 is provided with holes 47 at the level of the inlet conduit 40 for the pressure transmitting medium, and the conduit 40 is accessible through these holes, if desired even when the prop is in use.

The clamping jaw 41 is welded to the cylindrical section 2:: of the outer prop member, whilst the coupling ring 43 is detachably connected by means of threading 49 to the outer cylindrical section 2b, with a packing 48 interposed between them.

The coupling ring 43 has an annular flange 43a which extends substantially radially inwards, and all the valves between the outer and inner prop members associated with the compression chamber 8a and the cylindrical annular chamber 8 connected thereto, are disposed in this flange. The accompanying drawing only depicts the spring loaded excess pressure valve 50, and the housing of this valve is of a length approximately equal to the radial width of the flange 43a. The spring loaded inlet valve and the manually adjustable pressure relief valve are not shown but are also mounted within the sealing flange 43a of the coupling ring 43.

The inner surfaces of the coupling ring 43, in contrast with the FIGURE 6 illustration, may run flush with the inner wall of the outer prop member 2. It is also possible to so construct the coupling ring 43 that the latter encloses the end of the outer cylindrical section 2]) in sleeve fashion not only at the outer side, but also at the inner side.

FIGURE 6 shows that the radial width of the cylindrical annular chamber 8 between the inner and outer prop members is about six times the wall thickness of the bellows 3 or the bellows 38. The inner prop member 1 and the outer proper member 2 are guided one in the other by guide means (not shown) so that only a small amount of relative rotation is possible between these prop members when there is a relative longitudinal shifting.

As can be seen from FIGURE 6, the surfaces by means of which the inner marginal beads 3b, 38b of the bellows, associated with the inner prop member 1, are clamped are constituted by the opposed end faces of a closure plate arranged on the inner end of the cylindrical part 1a of the inner prop member, a clamping plate 54, and at least one intermediate washer 55 provided between the closure and clamping plates. The clamping plate 54 is displaceable on a screw-threaded bolt 52, which projects from the closure plate 51 axially in relation to the compression chamber 8a of the prop, and is adapted to be fastened against this closure plate 51, or the interposed washer 55, by means of a threaded nut 53.

The inner marginal beads 3b, 38b of the bellows are of smaller diameter than the outer diameter of the cylindrical part 10 of the inner prop member, and the marginal bead 3b is mounted in an annular groove of the closure plate 51, which is of larger cross-sectional area than the marginal bead 3b. The annular groove is bounded at the end by the washer 55, which is of larger diameter than the closure plate 51, and has at its outer edge a rim 16 which projects in bead fashion from the closure plate and the clamping plate. The marginal bead 38b of the inner bellows 38 is clamped towards the interior of the prop between the washer 55 and the clamping plate 54, this latter plate being slightly smaller in diameter than the washer 55.

Mounted on the outer end of the screw bolt 52, which projects into the compression chamber 8a of the prop, is a guide plate 36, similar to the arrangement illustrated in FIGURE 5, which is provided with perforations 36a of large area. The medium for operating the prop can flow through these perforations 36a from the compression chamber 8a between the guide plate 36 and head plate 17 into the annular chamber 8 between the inner and outer prop members, and inversely.

As in the embodiments of FIGURES 1 to 4, the constructions illustrated in FIGURES S and 6 can, without any complexity, be used in a position inverted through from that shown, so that the inner prop member 1 serves as the upper prop member, and the outer prop member 2 as the lower prop member.

We claim:

1. In a pit prop, in combination, an outer pit prop member and an inner pit prop member extending only partly into said outer pit prop member, said members being coaxial and said inner pit prop member having at all times a portion extending outwardly beyond said outer pit prop member, the exterior diameter of said inner pit prop member being substantially less than the inner diameter of said outer pit prop member so that said members define between themselves an annular axially extending space; means carried by one of said members and slidably engaging the other of said members for guiding said members for movement telescopically with respect to each other along their common axis; and an elongated, fluid-tight, flexible sleeve located in said space and having a pair of opposed ends respectively connected fluid-tightly to said members, said sleeve, during telescopic movement of said members with respect to each other along their common axis, rolling between the inner surface of said outer member and outer surface of said inner member, and said sleeve defining in said outer member a compression chamber located on one side of said sleeve for receiving a fluid which will produce the telescopic movement of said members, whereby the area of sliding contact between said means carried by said one member and slidably engaging the other member can be reduced to a minimum and need not be relied upon for fluidtightness.

2. in a pit prop, in combination, an outer pit prop member and an inner pit prop member extending only partly into said outer pit prop member, said members being coaxial and said inner pit prop member having at all times a portion extending outwardly beyond said outer pit prop member, the exterior diameter of said inner pit prop member being substantially less than the inner diameter of said outer pit prop member so that said members define between themselves an annular axially extending space; means carried by one of said members and slidably engaging the other of said members for guiding said members for movement telescopically with respect to each other along their common axis; and an elongated, fluid-tight, flexible sleeve located in said space and having a pair of opposed ends respectively connected fluidtightly to said members, said sleeve, during telescopic movement of said members with respect to each other along their common axis, rolling between the inner surface of said outer member and outer surface of said inner member, and said sleeve defining in said outer member a compression chamber located on one side of said sleeve for receiving a fluid which will produce the telescopic movement of said members, whereby the area of sliding contact between said means carried by said one member and siidably engaging the other member can be reduced to a minimum and need not be relied upon for fluidtightness, the length of said sleeve being at least equal to the maximum stroke of said members during telescopic movement thereof one with respect to the other.

3. In a pit prop, in combination, an outer pit prop member and an inner pit prop member extending only partly into said outer pit prop member, said members being coaxial and said inner pit prop member having at all times a portion extending outwardly beyond said outer pit prop member, the exterior diameter of said inner pit prop member being substantially less than the inner diameter of said outer pit prop member so that said members define between themselves an annular axially extending space; means carried by one of said members and slidably engaging the other of said members for guiding said members for movement telescopically with respect to each other along their common axis; and an elongated, fluid-tight, flexible sleeve located in said space and having a pair of opposed ends respectively connected fluid-tightly to said members, said sleeve during telescopic movement of said members with respect to each other along their common axis, rolling between the inner surface of said outer member and outer surface of said inner member, and said sleeve defim'ng in sa'd outer member a compression chamber located on one side of said sleeve for receiving a fluid which will produce the telescopic movement of said members, whereby the area of sliding contact between said means carried by said one member and slidably engaging the other member can be reduced to a minimum and need not be relied upon for fluid-tightness, said sleeve being fixed to said inner member at the end thereof which is located within said outer member and said sleeve being fixed to said outer member at a portion thereof which is spaced substantially from the end of said outer member which surrounds said inner member.

4. In a pit prop, in combination, inner and outer coaxial pit prop members, said inner member extending only in part into said outer member and having at all times a portion extending beyond said outer member, said outer member having a closed end located at all times beyond said inner member and an opposed annularend surrounding said inner member, the outer diameter of said inner member being substantially smaller than the inner diameter of said outer member so that the portion of said inner member which extends into said outer member defines with the latter an elongated annular space; a guide plate located within said outer member slidably engaging the inner surface thereof and located between said closed end of said outer member and the end of said inner member which is directed toward said closed end of said outer member and located within said outer member, said plate being formed with cutouts passing therethrough; connecting means connecting said plate to said inner member so as to be immovable with respect thereto; and an elongated, flexible, fluid-tight .sleeve located in said annular space and respectively having opposed ends fixed fluid-tightly to said members, said sleeve defining a compression chamber between said sleeve and said closed end of said outer member.

5. In a pit' prop, in combination, inner andouter coaxial pit prop members, said inner member extending only in part into said outer member and having at all times a portion extending beyond said outer member, said outer member having a closed end located at all times beyond said inner member and an opposed annular end surrounding said inner member, the outer diameter of said inner member being substantially smaller than the inner diameter of said outer member sothat the portion of said inner member which extends into said outer member defines with the latter an elongated annular space; a guide plate located within said outer member. slidably engaging the inner surface thereof and located between said closed end of said outer'member and the end of said inner member which is directed towithin said outer member, said plate being formed with cutouts passing therethrough; connecting means connecting said plate to said inner member so as to be immovable with respect thereto; and an elongated, flexible fluid-tight sleeve located in said annular space and respectively having opposed ends fixed fluid-tightly to said members, said sleeve defining a compression chamber between said sleeve and said closed end of said outer member, one end of said sleeve being fixed to said inner member between the end thereof which is directed toward said closed end of said outer member and said guide plate and the other end of said sleeve being fixed to said outer member at a portion thereof spaced substantially from said annular end of said outer member which surrounds said inner member, and said sleeve rolling between the outer surface of said inner member and the inner surface of said outer member during telescopic movement of said members one with respect to the other.

6. In a pit prop as recited in claim 1, said outer member including a pair of tubular sections axially spaced from each other but located closely adjacent to each other and annular coupling means coupling said sections to each other, said coupling means clamping an end of said flexible sleeve to one of said tubular sections.

7. In a pit prop as recited in claim 1, said outer mem ber including a pair of tubular sections axially spaced from each other but located closely adjacent to each other and annular coupling means coupling said sections to each other, said coupling means clamping an end of said flexible sleeve to one of said tubular sections, said coupling means having an annular flange extending radially between said tubular sectionstoward' the 7 common axis of saidmembers and sealing means providing a fluid-tight seal between the ends of said sections and said flange.

8. In a pit prop, in combination, inner and outer coaxial pit prop members, said inner member extending only in part into said outer member and havmg at all times a portion extending beyond said outer member,.

said outer member having a closed end located beyond said inner member and an opposed annular end surrounding said inner member, said inner member having an exterior diameter substantially smaller than the interior diameter of said outer member so that the portion of said inner member which extends into said outer member defines with the latter an elongated annular space, said outer member being composed of a pair of tubular sections slightly spaced axially one from the other; means carried by one of said members and slidably engaging the other of saidmembers for guiding said members for telescopic movement one with respect to'the other along.

their common axis; an elongated flexible fluid-tight sleeve located in said space, fluid-tightly fixed at oneend to the same to each other and clamping the end of said sleeve which extends between said sections to one of said sections in a fluid-tight manner, said coupling means" having an inwardly directed annular flange extending between said members and said sleeve defining with said closed end of said outer member a compression chamber which communicates with said flange; and valve means carried by said flange for participating in the control of fluid to and from said chamber.

9. In a pit prop, in combination, inner and outer coaxial pit prop members, said inner member extending only in part into said outer member and having at all times a portion extending beyond said outer member, said outer member having a closed end located beyond said inner member and an opposed annular end surrounding said inner member, said inner member having an ex terio'r diameter substantially smaller than the interior diameter of said outer member so that the portion of said inner member which extends into said outer member defines with the latter an elongated annular space, said outer member being composed of a pair of tubular sections slightly spaced axially one from the other means; carried by one of said members and slidably engaging the other of said members for guiding said members for telescopic movement one with respect to the otheralong their common axis; an elongated flexible fluid-tight sleeve located in said space, fluid-tightly fixed at one end to said inner member, and having an opposed end located between said section of said outer member; annular coupling means connected with said sections for connecting the same to each other and clamping the end of said sleeve which extends between said sections to one of said sections in a fluid-tight manner, said coupling means having an inwardly directed annular flange extending between said members and said sleeve defining with said closed end of said outer member a compression chamber which communicates with said flange; and valve means carried by said flange for participating in the control of fluid to and from said chamber, said valve means including a plurality of valves each having an axis extending radially with respect to the common axis of said members and said valves being circumferentially distributed about the common axis of said members.

10. In a pit prop, in combination, inner and outer coaxial pit prop members, said inner member extending only in part into said outer member and having at all times a portion extending beyond said outer member, said outer member having a closed end located beyond said inner member and an opposed annular end surrounding said inner member, said inner member having an exterior diameter substantially smaller than the interior diameter of said outer member so that the portion of said inner member which extends into said outer member defines with the latter an elongated annular space, said outer member being composed of a pair of tubular sections slightly spaced axially one from the other; means carried by one of said members and slidably engaging the other of said members for guiding said members for telescopic movement one with respect to the other along their common axis; an elongated flexible fluid-tight sleeve located in said space, fluid-tightly fixed at one end to said inner member, and having an opposed end located between said section of said outer member; annular coupling means connected with said sections for connecting the same to each other and clamping the end of said sleeve which extends between said sections to one of said sections in a fluid-tight manner, said coupling means having an inwardly directed annular flange extending between said members and said sleeve defining with said closed end of said outer member a compression chamber which communicates with said flange; valve means carried by said flange for participating in the control of fluid to and from said chamber; and means carried by said coupling means for covering said valve means to protect the latter from dust and other foreign matter.

11. In a pit prop, in combination, inner and outer coaxial pit prop members, said inner member extending only in part into said outer member and having at all times a portion extending beyond said outer member, said outer member having a closed end located beyond said inner member and an opposed annular end surrounding said inner member, the exterior diameter of said inner member being substantially smaller than the interior diameter of said outer member so that the portion of said inner member which is located within said outer member defines with the latter an elongated annular space, each of said members having a pair of clamping rings which define between themselves an annular chamber of predetermined cross sectional area and said rings having a pair of curved edges respectively directed toward each other and defining a mouth of reduced cross section through which said annular chamber communicates with said space; and an elongated flexible fluid-tight sleeve located in said space and having a pair of opposed enlarged annular ends respectively located in said annular chambers, the ends of said sleeve respectively being of a smaller cross sectional area than said chambers and said curved edges of said rings clamping said sleeve at portions thereof closely adjacent to said enlarged end portions, the distance between each pair of rings at said mouth thereof being smaller than the thickness of the enlarged end portion of the ring so that said clamping rings fluid-tightly clamp said sleeve to said members adjacent the ends of said sleeve; and guide means carried by one of said members and slidably engaging the other of said members for guiding said members for telescopic axial movement one with respect to the other.

12. In a pit prop, in combination, inner and outer coaxial pit prop members, said inner member extending at all times only in part into said outer member so that said inner member has at all times a portion extending beyond said outer member and said outer member having a closed end located beyond said inner member and an opposed annular end surrounding said inner member, said inner member having an exterior diameter substantially smaller than the interior diameter of said outer member so that the portion of said inner member which is located within said outer member defines with the latter an elongated annular space; guide means carried by one of said members and slidably engaging the other of said members for guiding said members for telescopic axial movement one with respect to the other; and an elongated flexible fluid-tight sleeve located in said space and having opposed ends respectively fixed fluid-tightly to said members, said sleeve defining with said closed end of said outer member a compression chamber adapted to receive a fluid under pressure for telescopically moving said members one with respect to the other, the radial thickness of said space being approximately equal to four times the thickness of said sleeve.

13. In a pit prop, in combination, inner and outer pit prop members coaxial with each other, said inner member extending only in part into said outer member and having at all times a portion extending beyond said outer member and said outer member having a closed end located beyond said inner member and an opposed annular end surrounding said inner member, the exterior diameter of said inner member being substantially smaller than the interior diameter of said outer member so that the portion of said inner member which extends along the interior of said outer member defines with the latter an elongated annular space; guide means carried by one of said members and slidably engaging the other of said members to guide said members for telescopic axial movement one with respect to the other; and a pair of flexible sleeves located next to each other in said space and each having opposed ends fluid-tightly connected with said members, one of said sleeves being located nearer to said closed end of said outer member than the other sleeve and defining .a compression chamber therewith, and at least said one sleeve being fluid-tight.

14. In a pit prop, in combination, inner and outer coaxial pit prop members, said inner member extending only at a portion thereof into said outer member and having at all times a portion extending beyond said outer member and said outer member having a closed end located beyond said inner member and an opposed annular end surrounding said inner member, said inner memher having an exterior diameter substantially smaller than the interior diameter of said outer member so that the portion of said inner member which extends along the interior of said outer member defines with the latter an elongated annular space, said outer member being composed of a pair of tubular sections axially spaced slightly from each other; annular coupling means coupling said sections to each other and including an inwardly directed flange extending radially between said sections beyond the inner surface of said outer member into said space; a guide plate formed with cutouts passing therethrough and located 21 within said outer member between said closed end thereof and said inner member in slidable engagement with the inner surface of said outer member; connecting means connecting said guide plate to said inner member so as to be immovable with respect thereto, said flange cooperating with said plate to limit the telescopic movement of said members one with respect to the other in one direction; and an elongated flexible fluid-tight sleeve located in said space, having one end fluid-tightly connected with said inner member, and having an opposed end fluid-tightly connected to said outer member between said flange of said coupling means and the section of said outer member which is most distant from said closed end thereof, said sleeve defining a compression chamber with the interior of said outer member at the side of said sleeve between 15 2 949 395 22 the latter and said closed end of said outer pit prop member.

References Cited in the file of this patent UNITED STATES PATENTS 1,038,636 Oxnard Sept. 17, 1912 1,039,157 Mackintosh Sept. 24, 1912 1,492,158 Caretta Apr. 29, 1924 1,508,654 Hales Sept. 16, 1924 1,928,368 Coffey Sept. 26, 1933 2,671,470 Boteler Mar. 9, 1954 2,673,573 Fawick Mar. 30, 1954 2,895,494 Adelson July 21, 1959 2,914,089 Allinquant Nov. 24, 1959 Reuter Aug. 23, 1960