[0001] This invention relates to pipe clamps.

[0002] This invention is concerned with a pipe clamp used for joining together two lengths of plastic pipe and more particularly two lengths of large to very large diameter pipes. Specifically the invention is concerned with a pipe clamp of the kind for clamping together two lengths of pipe of substantial wall thickness, the pipe clamp comprising a clamping unit arranged to surround the ends of the pipes and an inner member arranged to be inserted into the adjacent ends of the pipes, the clamping unit being formed by a plurality of clamping members and pressurising means adapted to draw the clamping members together to clamp the pipes against the inner member. Such a pipe clamp is hereinafter referred to as "a pipe clamp of the kind set forth" .

[0003] Numerous pipe clamps (not necessarily pipe clamps of the kind set forth) are disclosed in the patent literature. These include US Patent Specification No. 1 ,532,596 (Madsen); French Patent Specification No. 724,766 (English Steel Corporation); European Patent Specification No. 039 0747 (Geberit) and International Publication WO 00/77435 (Cartelage). In these arrangements the clamping unit comprises two, three or four clamping members. Further in pipe claims of the kind set forth the inner member is provided with peripheral grooves with the intention that the clamping units forces the wall of the pipe to distort into such grooves. The arrangements described in the specifications may well be a satisfactory for clamping together pipes having a small wall thicknesses and which are used in carrying fluids at relatively low pressures. I have found however that these arrangements are not satisfactory in clamping together large diameter pipes such as 110 mm to 710 mm outside diameter pipes with wall thicknesses from 10 mm up to 40 mm and which are capable of carrying fluids at as much as 12 to 14 Bar. This because inter alia, I have found, such thick walls of the pipes are too rigid to distort into the grooves. Furthermore with only four or less pressurising means it is not possible for workmen to apply sufficient pressure on the clamping members to apply sufficient inward pressure clamping the pipe satisfactorily against the inner member.

[0004] According to one aspect of the invention there is provided a pipe clamp of the kind set forth comprising at least five clamping members and pressurizing means, preferably comprising nut and bolt sets, between each of the clamping members to draw them together.

[0005] The inner member preferably has a central peripheral flange which projects beyond the level of the pipes. The clamping members preferably have recesses into which the edge of the flange is received. This arrangement will hold the inner member from moving relative to the clamping unit.

[0006] The inner member is preferably provided with a pair of teeth located on each side of the flange. The teeth are preferably of a right angle triangular section with the wall closer to the flange being normal to the inner member. The height of the teeth is preferably between 2 mm and 5 mm preferably about 3 mm.

[0007] The clamping members each comprise a pair of part annular members joined at their ends by radial plates, the inside edges of the annular members serving as clamping feet. The length and/or disposition of the feet is such that they engage the pipe between the radial locations of the teeth. [0008] An extension portion extends beyond the outer tooth on each side of the flange to limit the possibility of the pipe bending about the location of the flange.

[0009] An embodiment of the invention will now be described by way of example with reference to the accompanying drawings.

[0010] In the drawings :-

Figure 1 is a side view, partially in section, of an arrangement comprising two pipes connected together by a pipe clamp of the invention;

Figure 2 is a section on line 2 - 2 of Figure 1 ;

Figure 3 is a detail section on line 3 - 3 of Figure 2 with the nut and bolt set omitted for clarity;

Figure 4 is a perspective view of a clamping member;

Figure 5 is an outside view of a sleeve; and

Figure 6 is an end view of the sleeve.

[0011] Referring now to the drawings there is shown a pipe clamp 10 of the invention used for clamping together two heavy-duty water pipes 12 and 14 of an outside diameter of 630 mm and a wall thickness of 46.2 mm. The pipes 12 and 14 comprise high-density polyethylene (HDPE) and are capable of withstanding up to 14 Bar internal pressure. The length of the pipes is nine metres and the mass of each pipe is slightly less than eight hundred kilograms.

[0012] The pipes 12 and 14 are connected together by a pipe clamp 10 of the invention, The pipe clamp 10 comprises an outer clamping unit 20 and an inner sleeve 22. [0013] The clamping unit 20 comprises five clamping members 24. Each clamping member 24 consists of a pair of robust parallel flat annular members 26 joined at their ends by robust radial end plates 28. The end plates 28 all are substantially rectangular in shape with rounded upper corners 30. The lower ends 32 of the clamping members 24 are slightly narrower than the majority portion of these members and their outside surfaces 34 are tapered inwardly. The lower ends 32 extend beyond the lower edge of the end plate 28 to form clamping feet which are flat. The inner surfaces 38 of the clamping feet 36 are shaped to lie on the circumference of a nominal circle, which circumference comprises the lengths of the inner surfaces 38 plus sixty millimetres.

[0014] At the centre of the lower edge 39 of each end plate 28 is a slot 40. The slot 40 is in the shape of the frustum of an isosceles triangle with its upper sides at a very acute angle to one another.

[0015] Near the upper end of each plate 28 is a bolt hole 42.

[0016] The inner sleeve 22 has an axial length of about one and a half times the width of the end plate 28. The sleeve 22 has a large central flange 44. On each side of the flange 44 are a pair of tooth rings 46 and 48 of right angled triangular section. Each ring comprises a front face 50 standing normal to the outside surface of the sleeve 22 by about 3 mm high and facing the flange 44 and an outer inclined face 52 joining the front face 50 at a sharp corner 53. The distance between the front face 50 of each outer ring 48 to the beginning of the inclined face 52 of the adjacent inner ring 46 is approximately the same as the distance between the front face 50 of the inner ring 46 and the adjacent surface 54 of the flange 44. [0017] The sleeve 22 has an extension portion 56 at each end distanced from the outer ring 48 by about half of the distance between the tooth rings 48 and 46. A low flange 57 having a flat peripheral surface 58 about two thirds of the width of the flange 44 is provided at the outer end of each extension portion 56. The flange 57 projects upwardly by the same height as the tooth rings 46 and 48. The extension portions 56 and the flanges 57 serve to limit the possibility of the pipes bending about the location of the outer tooth rings 48.

[0018] The facing end plates 28 of adjacent clamping members 24 are connected by pressurising means in the form of nut and bolt sets 60. The diameter of the shank 62 of the bolt is smaller than the diameter of the bolt holes 40 of the end plates 28 so that, when the nut and bolt sets are loose, the clamping members 24 can swivel relative to each other.

[0019] The pipe clamp 10 is used as follows:- One half of the sleeve 22 is inserted into the end of one of the pipes (say 12) so that the flange 44 bears against the end face 64 of the pipe. The other pipe 14 is now fitted over the other half of the sleeve 22 until its end face 66 is close to the flange 44. Four of the clamping members 24 are connected together by nut and bolt sets 58 which are loose. This enables the clamping members 24 to swivel relative to each other to permit the clamping members to surround slightly less than about four fifths of the circumference of the pipes 12 and 14. The clamping members 24 are manipulated so that the outer edge of the central flange 44 fits into the slots 40 in the end plates 28.

[0020] The fifth clamping member 24 is inserted between the first and fourth clamping members and is connected thereto by nut and bolt sets 60 passing through the bolt holes 40. The slots 40 in the end plates 28 of the fifth clamping member receive the edge of the flange 44. The nut and bolt sets 60 are tightened to an even finger tightness in which case the distance between the end plates 28 of all the clamping members 24 is about 12 mm. Now using a pair of spanners, the nut and bolt sets 60 are tightened evenly until the clamping unit 20 clamps the pipes 12 and 14 firmly against the sleeve 22. When this occurs, the distance between end plates 28 is about 6 mm. The clamping unit will have compressed the wall of each pipe 12 and 14 so that the diameters of the pipes are reduced by a little under ten millimetres. The tooth rings 46 and 48 bite into the inner surfaces 68 and 70 of the pipes 12 and 14. It will be noted that the feet 36 will engage the outer surfaces 72 and 74 of the pipes 12 and 14 between the location at which the tooth rings 46 and 48 engage the inner surfaces 68 and 70 of the pipes 2 and 14.

[0021] I have found that when the two pipes 12 and 14 are connected together by the pipe clamp 10 as aforesaid, the connection can withstand an internal pressure in the pipes of up to 14 Bar. By having the flange 44 entering the slots the location of the sleeve relative to the clamping members will be substantially fixed. Further I have found that by having five nut and bolt sets 58 it is possible for workmen using only conventional spanners can tighten the clamping members together as described above. These workmen need be only semi-skilled workers and working in teams of three or four can apply a pipe clamp in about fifteen minutes.

[0022] It will be appreciated that when a pipe line consisting of pipes joined by the pipe clamps 10 has served its purpose, the pipe clamps can be disassembled and removed from the pipes. The pipes can then be moved separately and can be used elsewhere as can the pipe clamps. Thus a pipe line consisting of pipes joined by the pipe clamps can be prepared at a substantially less cost and time than it would take to prepare the pipe line using welding which is currently the most widely used method of connecting together large pipes.

[0023] The invention is not limited to the precise constructional details hereinbefore described and illustrated. For example a pipe clamp for use with larger pipes, say of a metre in diameter, more than five clamping members may have to be provided to enable sufficient clamping force to be achieved by workmen using conventional spanners. The pipe clamps can also be used for joining pipes that form a pipe line conveying clean water such as water being supplied to a fire damping nozzles.