GB2536243A

GB2536243A - Pipe coupling

Info

Publication number: GB2536243A
Application number: GB1504006.6A
Authority: GB
Inventors: Richard Webb Ian; John Thornton Taylor Neil
Original assignee: Taylor Kerr Couplings Ltd
Current assignee: Taylor Kerr Couplings Ltd
Priority date: 2015-03-10
Filing date: 2015-03-10
Publication date: 2016-09-14
Also published as: WO2016142659A1; GB201504006D0

Abstract

The present invention relates to a pipe coupling 100. The coupling 100 comprises a tubular casing 102 having a longitudinal gap 110 between a first free end and a second free end for fitting around a pipe, and a tensioning system 104. The tensioning system 104 comprises two tensioning members 106, 108, one coupled to the first free end of the casing, the other coupled to the second free end. The tensioning members 106, 108 comprise at least one engaging arm, and at least one engaging surface. The tensioning system 104 also comprises at least one fastener. The engaging arm of the first tensioning member 106 slidably engages with the engaging surface of the second tensioning member 108, and vice versa. Upon tightening the fastener, the first tensioning member 106 and the second tensioning member 108 are drawn together to tighten the casing 102 around the outer surface of the pipe, the engaging arms acting on the respective engaging surfaces to substantially prevent the first tensioning member 106 from rotating relative to second tensioning member 108 about the longitudinal axis of the tensioning members 106, 108.

Description

PIPE COUPLING

The present invention relates to pipe couplings and in particular to a pipe coupling having a tensioning system for tightening the coupling around the outer surface of the pipes.

A wide variety of pipe couplings for connecting together two pipe ends in a fluid tight manner are known. In order to enable the coupling to function for slightly undersized and slightly oversized pipes, a longitudinal gap between free ends of the casing of the pipe coupling is required.

One known example of a pipe coupling for connecting together two plain-ended pipes in a fluid-tight manner comprises a tubular casing formed with a longitudinal gap, a sealing gasket of resilient flexible material typically of rubber or synthetic rubber, arranged within the casing, and tensioning means for reducing the width of the longitudinal gap so as to tighten the casing around the gasket. In use, the sealing gasket is placed around the adjacent pipe ends and the tensioning means are tightened to clamp the gasket against the outer surfaces of the pipe ends to form a fluid-tight seal.

In use, the fluid pressure in a pipeline tends to deform the casing, and in particular deforms the casing in the region of the free ends on either side of the longitudinal gap. The deformation of the casing reduces the forces acting on the gasket in the region of the free ends. The reduction in forces acting on the gasket decreases the maximum rated fluid pressure for the pipe coupling. In known pipe couplings, additional reinforcing material, additional welding and large and relatively heavy trunnion bar mechanisms have been used to counteract the deformation of the casing and the resultant reduction in forces acting on the sealing gasket. It would therefore be desirable to provide a novel pipe coupling having improved resistance to deformation in the region of the free ends of the casing, and thus improved resistance to fluid pressure. It would be particularly desirable to provide such a pipe coupling that is lighter, smaller and less expensive to manufacture than pipe couplings having equivalent fluid pressure ratings.

According to the present invention, there is provided a pipe coupling comprising: a tubular casing, having a longitudinal gap between a first free end and a second free end, for fitting around a pipe; and a tensioning system for tightening the casing around the outer surface of the pipe. The tensioning system comprises: a first tensioning member coupled to the first free end of the casing, comprising at least one engaging arm, and at least one engaging surface; a second tensioning member coupled to the second free end of the casing, comprising at least one engaging arm, and at least one engaging surface; and at least one fastener. The at least one engaging arm of the first tensioning member is -2 -configured to slidably engage with the at least one engaging surface of the second tensioning member. The at least one engaging arm of the second tensioning member is configured to slidably engage with the at least one engaging surface of the first tensioning member. Upon tightening the or each fastener, the first tensioning member and the second tensioning member are drawn together to tighten the casing around the outer surface of the pipe, the engaging arms acting on the respective engaging surfaces to substantially prevent the first tensioning member from rotating relative to second tensioning member about the longitudinal axis of the tensioning members.

Advantageously, providing tensioning members having an engaging arm and corresponding engaging surface enables the tensioning system to tighten the casing around the pipe more effectively. The engaging arm acts on the corresponding engaging surface to prevent the tensioning members from rotating about their longitudinal axes, and therefore the tensioning force is transmitted to the casing at a location between the centre line of the fastener and the outer surface of the pipe. In addition, by preventing relative rotation between the tensioning members, the fasteners are protected from any bending forces and thus can operate more efficiently.

As used herein, the term "axial" is used to refer to the direction defined by the longitudinal axis of the pipe and the term "radial" is used to refer to a direction defined by a radius of the pipe. As will be appreciated, the longitudinal axis of a tensioning member is substantially parallel to the longitudinal axis of the pipe.

In a preferred embodiment, each engaging arm comprises at least one engaging tooth, and each engaging surface comprises a plurality of recesses. The or each engaging tooth is configured to engage with each of the respective plurality of recesses progressively as the tensioning members are drawn together. Preferably, the engaging surface recesses form a linear ratchet, the or each engaging tooth acting as a pawl. As the tensioning members are drawn together the or each engaging tooth progressively engages with successive recesses on the engaging surface.

Each recess preferably comprises two surfaces, the first surface substantially facing an engaging direction of the tensioning members, and the second surface opposing the engaging direction, such that the plurality of recesses form a triangular saw-tooth arrangement. The first surface and the second surface are each preferably substantially planar. The angle between the first surface of each recess and the engaging surface is preferably between about 90 degrees and about 120 degrees, more preferably between about 95 degrees and about 105 degrees. The or each engaging tooth may comprise two -3 -surfaces, the first surface substantially opposing the engaging direction, and the second surface substantially facing the engaging direction. The first surface of the engaging tooth is configured to engage with the first surface of the recess. The first surface of the engaging tooth may be configured such that it lies parallel to the first surface of the recess when the engaging tooth is engaged in the recess.

Advantageously, providing a ratchet type system where the engaging arm has an engaging tooth and the engaging surface has corresponding recesses enables the pipe coupling to be more securely fitted to the pipe. When engaged, the ratchet type system reduces the force acting on the fastener.

In addition, as the tensioning members are drawn together, the tensioning members attempt to rotate about their longitudinal axis. As described above, the engaging arm and engaging surface interact to prevent such relative rotation, and act to further engage the engaging tooth in the corresponding recess.

Each engaging surface may comprise two, three, four, five or more recesses. In a preferred embodiment each engaging surface comprises three engaging recesses. Each engaging arm may comprise one, two, three or more engaging teeth. In a preferred embodiment, each engaging arm comprises one engaging tooth.

Each of the first tensioning member and the second tensioning member may comprise two, three, four, five or more engaging arms and corresponding engaging surfaces. In one 20 preferred embodiment, each tensioning member comprises three engaging arms and corresponding engaging surfaces.

Preferably, each engaging surface is provided in a channel configured to guide the respective engaging arm as the first tensioning member and the second tensioning member are drawn together. Advantageously, the channel acts to maintain the alignment of the tensioning members in the axial direction of the pipe. The channel preferably comprises three walls, a first side wall, a second side wall, and a wall comprising the engaging surface. The first wall and the second wall are preferably substantially perpendicular to the wall comprising the engaging surface. The depth of the channel, that is to say the height of the first side wall and second side wall, is preferably substantially equal to the thickness, in the radial direction of the engaging arm. The width of the channel, along the longitudinal axis of the tensioning member, is preferably between about 105% and about 125% of the width of the engaging arm. -4 -

Each engaging arm and each engaging surface is preferably provided on the outer surface of the corresponding first tensioning member and second tensioning member, the outer surface being opposite the surface facing the pipe.

The first tensioning member preferably comprises at least one projection for engaging with a corresponding through hole in the first free end of the casing, and the second tensioning member preferably comprises at least one projection for engaging with a corresponding through hole in the second free end of the casing, such that the first tensioning member and the second tensioning member are coupled to the casing.

As the tensioning members are drawn together as the fastener is tightened, the casing is held relative to the tensioning members by the through hole interacting with the projection. In this way, mechanical fastenings between the casing and the tensioning members may not be required.

The at least one projection on the first tensioning member is preferably provided on a surface which faces the second tensioning member, and the at least one projection on the second tensioning member is provided on a surface which faces the first tensioning member. Alternatively, the at least one projection may be provided on the outer surface of the tensioning member, the outer surface being opposite the surface facing the pipe.

The length of the or each projection may be substantially equal to the thickness of the casing material.

Each of the first tensioning member and the second tensioning member may comprise two, three, four, five or more projections, and the first free end and the second free end of the casing then comprises a corresponding two, three, four, five or more through holes. In one preferred embodiment, the tensioning members each comprise three projections.

The projections may have any cross-sectional shape, but in a preferred embodiment the cross-sectional shape of the projection is circular.

Alternatively, or in addition to the use of projections and corresponding through holes to couple the casing to the tensioning members, the first free end of the casing may be coupled to the first tensioning member by at least one fixing, and the second free end of the casing may be coupled to the second tensioning member by at least one fixing.

The first free end is preferably configured to extend around the first tensioning member to be coupled to the first tensioning member on the outer surface of the first tensioning member, the outer surface being opposite the surface facing the pipe, and the second free end is preferably configured to extend around the second tensioning member -5 -to be coupled to the first tensioning member on the outer surface of the second tensioning member.

The first free end and the second free end of the casing are each preferably folded back on themselves to form coupling portions for coupling with the respective tensioning 5 members. The tensioning members may be used as formers during the folding process. Where the casing is coupled to the tensioning members on the outer surface thereof, the casing may be coupled to the tensioning members using fasteners, such as screws. In this embodiment, the tensioning members comprise threaded holes, preferably blind threaded holes for receiving the screws. The coupling portion of the casing, in this case, comprises a further tab portion which is folded around the outer surface of the tensioning member.

Each engaging surface may comprise a guide ramp configured to guide the engaging arm onto the engaging surface as the tensioning members initially engage as they are drawn together. The guide ramp is provided at the edge of the engaging surface which faces the opposing tensioning member. The guide ramp preferably has an angle of between about 5 degrees and about 25 degrees from the engaging surface. The guide ramp may be between about 10% and about 30% of the length of the engaging surface.

The first tensioning member is formed from a single piece of material, and the second tensioning member is formed from a single piece of material. Advantageously, this may reduce the manufacturing costs. The tensioning members may be cast, and may not require any subsequent machining processes, which may yet further reduce manufacturing costs. Known pipe couplings require additional manufacturing processes such as welding to produce the finished product. Thus the present invention may significantly improve the manufacturing efficiency.

The first tensioning member may comprise at least one threaded insert for receiving the at least one fastener.

The first tensioning member and the second tensioning member are preferably substantially symmetrical about a mid-point along the longitudinal length of the tensioning member. In a preferred embodiment, the first tensioning member and the second tensioning member are substantially identical.

Advantageously, providing substantially identical tensioning members reduces the manufacturing costs and complexities of the tensioning system.

The casing may be of generally U-shaped cross-section having a web portion with flanges projecting radially inwardly from the axial ends of the web portion to define an annular channel. -6 -

The pipe coupling may further comprise a tubular sealing gasket located inside the casing. In use of the pipe coupling, as the casing is tightened around the pipe ends, the casing presses the sealing gasket against the outer surfaces of the pipe ends to form seals. The first pivoting member and the second pivoting member press against the bridge plate, which in turn presses the sealing gasket against the outer surfaces of the pipe ends to form seals in the region of the longitudinal gap between the two free ends of the casing. Suitable sealing gaskets for use in a pipe coupling of this construction will be known to the skilled person, and may be made of resilient flexible material typically of rubber or synthetic rubber, or any other suitable material.

The pipe coupling may further comprise a bridge plate located inside the casing for spanning the longitudinal gap between the first free end and the second free end of the tubular casing. The bridge plate may be coupled to one of the first free end or the second free end of the tubular casing.

The bridge plate may be welded, bonded or soldered to one of the first free end or the second free end of the tubular casing. Coupling the bridge plate to the tubular casing enables the pipe coupling to be installed more easily.

The tubular casing will typically be formed of a strip of metal or other material formed into a tube with a gap extending longitudinally of the casing between the free ends of the strip, wherein the free ends of the strip are interconnected by the tensioning system. The bridge plate will therefore typically be formed in a part-cylindrical shape with a radius of curvature similar to that of the casing. The casing on either side of the longitudinal gap overlaps with the bridge plate.

In certain embodiments of the invention, where provided, the bridge plate may extend substantially around the full circumference of the pipe coupling. In these embodiments, the tubular casing comprises an outer casing as described above and the bridge plate as an inner casing fitted within the outer casing. Preferably, the inner casing is fitted entirely within the outer casing. The outer casing and inner casing preferably both have longitudinal gaps wherein the gap in the inner casing is circumferentially offset from the gap in the outer casing. A suitable arrangement of outer and inner casings would be known to the skilled person and is described, for example, in GB-A-2 275 089.

Preferably, a layer of fire-resistant thermally-insulating material is disposed between the inner and outer casings whereby the inner and outer casings are thermally insulated from one another. This feature enables a fire-resistant pipe coupling to be provided which can withstand extremely high temperatures without deterioration. Details of a suitable fire -7 -shield for incorporating into the pipe coupling of the present invention can be found, for example, in EP-A-0 900 346.

The pipe coupling may further comprise at least one arcuate gripping ring having inwardly projecting gripping teeth, located in the tubular casing. The gripping ring preferably forms a complete ring. In a preferred embodiment a plurality of arcuate segments are provided which overlap to form a complete ring. The or each arcuate gripping ring is preferably frustoconical.

In the embodiment comprising a gripping ring, the ring is preferably formed in two segments. The segments comprise a major segment which subtends an arc of greater than 180° at the axis of the gripping ring and a minor segment which subtends an arc of less than 180° at the axis of the gripping ring. The casing is formed with a longitudinal gap and the tensioning means is arranged to reduce the longitudinal gap when tightened, the minor segment is located adjacent the longitudinal gap and the major segment is located to the side of the casing remote from the longitudinal gap, the major and minor segments overlapping one another on either side of the gap.

The pipe coupling may be suitable for any pipe having an external diameter of between about 21 mm and about 4500 mm. The pipe coupling of the present invention also accommodates typical pipe tolerances in accordance with, for example, BS EN 877:1999.

Any feature in one aspect of the invention may be applied to other aspects of the invention, in any appropriate combination. In particular, method aspects may be applied to apparatus aspects, and vice versa. Furthermore, any, some and/or all features in one aspect can be applied to any, some and/or all features in any other aspect, in any appropriate combination.

It should also be appreciated that particular combinations of the various features described and defined in any aspects of the invention can be implemented and/or supplied and/or used independently.

The invention will be further described, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows a perspective view of a pipe coupling according to one embodiment of the invention; Figure 2 shows an end view of the pipe coupling of Figure 1; Figures 3 show a tensioning system of the pipe coupling of Figures 1 and 2; Figure 4 shows a perspective view of the tensioning system of Figures 3; -8 -Figures 5 show a sequence of cross-sectional views A-A of the tensioning system of Figures 3 and 4 as tensioning members are drawn together; Figure 6 shows a perspective view of a pipe coupling according to a further embodiment of the invention; Figure 7 shows an end view of the pipe coupling of Figure 6; Figures 8 show a tensioning system of the pipe coupling of Figures 6 and 7; Figure 9 shows a perspective view of the tensioning system of Figures 8; Figure 10 show a sequence of cross-sectional views B-B views of the tensioning system of Figures 8 and 9 as tensioning members are drawn together; and Figure 11 shows a perspective view of a yet further embodiment of a tensioning system according to the invention.

Figures 1 and 2 show a pipe coupling 100 according to a first embodiment of the present invention. The pipe coupling 100 comprises a tubular casing 102, a sealing gasket (not shown) and a tensioning system 104. The tensioning system 104 comprises a first tensioning member 106 and a second tensioning member 108. The pipe coupling also comprises a bridge plate (not shown) provided within the casing.

The casing 102 is formed of a rolled steel strip, formed into a tube with a longitudinal gap 110 between the free ends of the strip. The axial end margins of the casing 102 are bent inwardly at right angles to a tubular web portion of the casing to form flanges 112 projecting inwardly towards the central axis of the casing.

The bridge plate (not shown), similarly to the casing 102, is formed of a rolled steel strip having a radius of curvature substantially equal to that of the casing 102. The casing 102 on either side of the longitudinal gap 110 overlaps the bridge plate. The axial length of the bridge plate is slightly less than that of the casing 102 so that the bridge plate fits inside the flanges 112 of the casing 102.

The sealing gasket (not shown) is of an elastomeric material, for example rubber or synthetic rubber. The inner surface of the sealing gasket is formed with raised sealing surfaces for contacting the outer surface of the pipe when the pipe coupling 100 is in place.

The sealing gasket fits inside the casing 102 and the bridge plate.

As can be seen in Figure 2, the first free end of the casing 102 is folded away from the interior of the casing 102 to form a first coupling portion 200. Similarly, the second free end of the casing 102 is folded away from the interior of the casing to form a second coupling -9 -portion 202. Each coupling portion is configured to couple the free ends of the casing to respective tensioning members 106 and 108.

The distal end of the first coupling portion 200 is folded in a direction opposing the second coupling portion 202 to form a first coupling portion tab 204. The distal end of the second coupling portion 202 is folded in a direction opposing the first coupling portion 200 to form a second coupling portion tab 206. The tab portions 204 and 206 are fixed to the respective tensioning members 106 and 108 by fasteners, as described in further detail below.

The coupling portions 200 and 202 are provided with cut-outs (not shown) to enable 10 fasteners to be provided through the tensioning members 106 and 108, and through the coupling portions 200 and 202.

The tensioning members 106 and 108 are shown in further detail in Figures 3. Figure 3(a) shows a first end view. Figure 3(b) shows a second end view, Figure 3(c) shows a bottom view, and Figure 3(d) shows a top view. The tensioning members 106 and 108 are substantially symmetrical about a mid-point along its the longitudinal axis, which means that the two tensioning members 106 and 108 are substantially identical. This reduces manufacturing costs, and simplifies assembly of the pipe coupling.

Each tensioning member 106, 108, comprises a main body 302 and a plurality of engaging arms 304 extending from the main body 302. In this example, the tensioning 20 member 106, 108 has three engaging arms 304a, 304b and 304c. The distal end of each engaging arm 304 has an engaging tooth 306.

Adjacent each engaging arm 304 along the longitudinal axis tensioning member 106, 108 is a channel 308. The channels 308 have a width of between about 105% and about 125% of the width of the engaging arms 304. The channels 308 extend across the entire transverse width of the tensioning member 106, 108. The channels comprise an engaging surface 310. In use, the engaging arms 304 are configured to engage with the engaging surfaces 310, described in further detail below.

Each engaging surface 310 comprises a plurality of recesses 312 that extend across each engaging surface 310 along the longitudinal axis of the tensioning member 106, 108.

Each of the plurality of recesses 312 comprises two surfaces to form a triangular saw-tooth arrangement. In this example each engaging surface 308 comprises three recesses 312. As will be appreciated, the engaging tooth 306 (a pawl) and the recesses 312 (a ratchet) form a linear ratchet and pawl arrangement.

The tensioning member 106, 108 comprises two through holes 314 and 316 each for receiving a fastener. One set of through holes 314, 316 of the tensioning members 106, 108 is provided with a press-ft threaded insert for receiving the fastener. In use, tightening the fastener draws the tensioning members 106 and 108 together. The operation of the pipe coupling is described below in further detail. As will be appreciated, the number of through holes provided for fasteners can be increased in dependence on the size of the pipe coupling, as required.

To facilitate secure coupling of the casing 102 to the tensioning members 106 and 108 a plurality of threaded blind holes 318 are provided in the tensioning member 106, 108.

Corresponding through holes are provided in the coupling portion tabs 204, 206. Fasteners (not shown) are used to secure the casing 102 to the tensioning members 106 and 108 by the coupling portion tabs 204, 206. As shown in Figures 1 and 2, the tensioning members 106 and 108 are provided on the outside surface of the casing 102 such that the coupling portions 200 and 202 are sandwiched between the tensioning members.

Figure 4 shows a perspective view of the tensioning members 106 and 108 in a partially engaged position. For ease of reference the casing 102 is not shown. As can be seen, engaging arm 304a engages with channel 308c, engaging arm 304b engages with channel 308b, and engaging arm 304c engages with channel 308a. In Figure 4, the engaging tooth 306 (not shown in Figure 4) of each engaging arm 304 is engaged with the first of the plurality of recesses 312 on the engaging surface 310. The engaging arms 304 and the channels 308 are interweaved to form a locking arrangement.

As shown in Figure 4, recesses 400, 402, 404 may be provided to reduce the weight, and cost, of the tensioning members.

Initially, the tensioning system 104 is in a disengaged state, as shown in Figure 5(a), where the engaging arms 304 are not in contact with the engaging surfaces 308. As the tensioning members 106 and 108 are drawn together by the fasteners (not shown) the engaging tooth 306 is guided onto the engaging surface 310 by the guide ramp 500. As the fastener is tightened, the engaging tooth 306 progressively slides along the engaging surface 310 until the tooth engages with the first recess. As the fastener is tightened still further, the engaging tooth 306 is forced into successive recesses as shown in Figures 5(b) and 5(c). Figure 5(c) shows the tensioning system in the final position. As the tensioning members are drawn together the free ends of the casing are drawn together, tightening the casing around a pipe.

In use, the fluid pressure within the pipes being coupled tends to deform the casing, and in particular deforms the casing in the region of the free ends on either side of the longitudinal gap. The forces are such that the free ends attempt to displace from each other in the transverse direction. Without restraining this movement, the forces acting on the gasket will decrease, and thus the maximum rated fluid pressure for the pipe coupling would be reduced. As shown in Figure 5(c), the transverse force acting on the tensioning system due to the fluid pressure within the pipes at, effectively, points 502a and 502b tends to rotate the tensioning members 106 and 108 relative to each other in the directions 504a and 504b respectively. The relative rotational movement of the tensioning members 106 and 108 is substantially prevented by the interaction of the engaging arms 304 and the engaging surfaces 310. Relative transverse movement of the tensioning members 106 and 108 is both substantially prevented by the ratchet and pawl arrangement of the engaging teeth 316 and the recesses 312, and by the fasteners.

If required, two frustoconical arcuate gripping rings having inwardly projecting gripping teeth may be provided in the casing. The rings are configured to extend around the entire circumference of the pipes, and over lap at their ends. The frustoconical shape of the rings enables one edge to act on the casing at the corner formed by the flanges 112, and the other edge to engage with the pipe. The gripping rings improve the pipe couplings resistance to axial forces.

A further embodiment of a pipe coupling according to the present invention is shown in Figures 6 to 10. Where components of the pipe coupling are the same as those described above with reference to Figures 1 to 5, like reference numerals have been used. The pipe coupling 600 comprises a tensioning system 602, again comprising a pair of tensioning members 604 and 606. The casing 102 is similar to that described above, and the pipe coupling operates in the same manner. However, as shown in Figure 7, each tensioning member is provided with a set of projections, in the form of pins 700 and 702 respectively, which engage with through holes in the coupling portions 704 and 706 of the casing 102. The pins and through holes improve the coupling between the casing and the tensioning members.

As can be seen from Figures 8, the tensioning member 604, 606 is otherwise substantially the same as the tensioning member 106, 108 described above. Thus the tensioning member 604, 606 comprises a main body 800 and engaging arms 802, engaging teeth 804, channels 806, engaging surfaces 808, recesses 810 and through holes for receiving fasteners 812 and 814. The pins 700, 702 are provided on the main body 800.

The arrangement of the main body 800 and the engaging arms 802 are substantially the same as the equivalent components described above.

Similarly to Figure 4, Figure 9 shows a perspective view of the further embodiment of the tensioning system 602. Figures 10 show the tensioning system 602 progressively engaging as fasteners (not shown) draw the two tensioning members together. The operation of the pipe coupling and tensioning system is the same as that described above, except that the pins 700, 702 and through holes in the coupling portions 704 and 706 act to improve the coupling between the casing and the tensioning members.

Finally, a yet further example of a tensioning system 1100 is shown in Figure 11. The tensioning system 1100 is substantially the same as the tensioning system shown in Figures 1 to 5, except that the engaging surfaces 310 do not comprise a plurality of recesses, and the engaging arms 304 do not comprise an engaging tooth. The operation of the tensioning system is substantially the same as the operation described above, except that there is no ratchet and pawl arrangement. Therefore, the engaging arm 304 simply slides progressively along the engaging surface 310. Nonetheless, the interaction between the engaging arms and the corresponding engaging surfaces prevent substantial relative rotation between the tensioning members 1102 and 1104.

Claims

CLAIMS1. A pipe coupling comprising: a tubular casing, having a longitudinal gap between a first free end and a second free end, for fitting around a pipe; and a tensioning system for tightening the casing around the outer surface of the pipe, the system comprising: a first tensioning member coupled to the first free end of the casing, comprising at least one engaging arm, and at least one engaging surface; a second tensioning member coupled to the second free end of the casing, comprising at least one engaging arm, and at least one engaging surface; and at least one fastener, wherein: the at least one engaging arm of the first tensioning member is configured to slidably engage with the at least one engaging surface of the second tensioning member; the at least one engaging arm of the second tensioning member is configured to slidably engage with the at least one engaging surface of the first tensioning member; and upon tightening the or each fastener, the first tensioning member and the second tensioning member are drawn together to tighten the casing around the outer surface of the pipe, the engaging arms acting on the respective engaging surfaces to substantially prevent the first tensioning member from rotating relative to second tensioning member about the longitudinal axis of the tensioning members.
2. A pipe coupling according to Claim 1, each engaging arm comprising at least one engaging tooth, and each engaging surface comprising a plurality of recesses, wherein the or each engaging tooth is configured to engage with each of the respective plurality of recesses progressively as the tensioning members are drawn together.
3. A pipe coupling according to Claim 1 or 2, each of the first tensioning member and the second tensioning member comprises two, three, four, five or more engaging arms and corresponding engaging surfaces.
4. A pipe coupling according to Claim 1, 2 or 3, wherein each engaging surface is provided in a channel configured to guide the respective engaging arm as the first tensioning member and the second tensioning member are drawn together.
5. A pipe coupling according to any of Claims 1 to 4, wherein each engaging arm and each engaging surface is provided on the outer surface of the corresponding first tensioning member and second tensioning member, the outer surface being opposite the surface facing the pipe.
6. A pipe coupling according to any of the preceding claims, wherein the first tensioning member comprises at least one projection for engaging with a corresponding through hole in the first free end of the casing, and the second tensioning member comprises at least one projection for engaging with a corresponding through hole in the second free end of the casing, such that the first tensioning member and the second tensioning member are coupled to the casing.
A pipe coupling according to Claim 5, wherein the projection on the first tensioning member is provided on a surface which faces the second tensioning member, and the projection on the second tensioning member is provided on a surface which faces the first tensioning member.
A pipe coupling according to Claim 5 or 6, wherein the length of the or each projection is substantially equal to the thickness of the casing material.
9. A pipe coupling according to Claim 5, 6 or 7, wherein each of the first tensioning member and the second tensioning member comprises two, three, four, five or more projections, and the first free end and the second free end of the casing comprises a corresponding two, three, four, five or more through holes.
10. A pipe coupling according to any of the preceding claims, wherein the first free end of the casing is coupled to the first tensioning member by at least one fixing, and the second free end of the casing is coupled to the second tensioning member by at least one fixing.A pipe coupling according to Claim 9, wherein the first free end is configured to extend around the first tensioning member to be coupled to the first tensioning member on the outer surface of the first tensioning member, the outer surface being opposite the surface facing the pipe, and the second free end is configured to extend around the second tensioning member to be coupled to the first tensioning member on the outer surface of the second tensioning member.A pipe coupling according to any of the preceding claims, wherein each engaging surface comprises a guide ramp configured to guide the engaging arm onto the engaging surface as the tensioning members initially engage as they are drawn together.A pipe coupling according to any of the preceding claims, wherein the first tensioning member and the second tensioning member are substantially identical.A pipe coupling according to any of the preceding claims, wherein the first tensioning member and the second tensioning member are substantially symmetrical about a mid-point along the longitudinal length of the tensioning member.A pipe coupling according to any of the preceding claims, wherein the first tensioning member comprises at least one threaded insert for receiving the at least one fastener.A pipe coupling according to any of the preceding claims, wherein the first tensioning member is formed from a single piece of material, and the second tensioning member is formed from a single piece of material.
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22.A pipe coupling according to any of the preceding claims, wherein the casing is of generally U-shaped cross-section having a web portion with flanges projecting radially inwardly from the axial ends of the web portion to define an annular channel.A pipe coupling according to any of the preceding claims, further comprising a tubular sealing gasket located within the casing.A pipe coupling according to any of the preceding claims, further comprising a bridge plate located inside the casing for spanning the longitudinal gap between the first free end and the second free end of the tubular casing.A pipe coupling according to Claim 19, wherein the bridge plate is coupled to one of the first free end or the second free end of the tubular casing.A pipe coupling according to any of the preceding claims, further comprising at least one arcuate gripping ring having inwardly projecting gripping teeth, located in the tubular casing.A pipe coupling substantially as herein described with reference to the accompanying drawings.