Abstract:
A pipe coupling for joining together the ends of two adjacent pipes includes a housing for receiving the ends of the two adjacent pipes, and a locking arrangement which includes an annular chamber, and a plurality of grippers radially moveable towards the central axis of the housing from an inoperative condition to an operative condition. Each gripper includes a gripping formation for operatively gripping a pipe inserted into a bore of the housing, and a locking formation for operatively engaging a corresponding locking formation on the housing so as to axially lock the gripper to the housing. Each locking arrangement also includes a locking ring for locking the grippers to the housing so that axial displacement of the locking ring under fluid pressure within the annular chamber causes radial displacement of the grippers into the operative condition.

Description:
BACKGROUND OF THE INVENTION 
   This invention relates to a pipe coupling. More specifically, the invention relates to a coupling which is designed to join together two adjacent pipes for conveying fluid under pressure. 
   Various different types of pipe couplings are known. Many of the known types of couplings include bolts or other similar fasteners which have to be installed in a particular manner or sequence, and this tends to complicate the installation of these couplings. In practice, users often fail to comply fully with the correct installation procedure with the result that these couplings are not always installed with maximum effectiveness. Furthermore, conventional pipe couplings often allow for movement of adjacent pipes within the coupling, i.e. they are not end restraining, and this can lead to weeping at the joint over time. 
   It is an object of the present invention to provide an alternative pipe coupling which is relatively easy to install, which does not include any bolts or other similar fasteners, and which is fully end restraining. 
   SUMMARY OF THE INVENTION 
   According to the invention there is provided a pipe coupling for joining together the ends of two adjacent pipes, the coupling including a housing which defines a generally central bore along a central axis of the housing for receiving the ends of the two adjacent pipes, and a locking arrangement at each end of the housing for locking the pipes to the coupling, each locking arrangement including:
         an annular chamber within the housing;   an inlet for allowing fluid into the chamber;   an annular seal which is arranged to move within the annular chamber axially of the housing;   a plurality of grippers which are radially moveable towards the central axis of the housing from an inoperative condition to an operative condition, each gripper including a gripping formation for operatively gripping a pipe inserted into the bore of the housing, and a locking formation for operatively engaging a corresponding locking formation on the housing so as to axially lock the gripper to the housing; and   at least one locking element between the annular seal and the grippers for locking the grippers to the housing and to a pipe end within the housing, the or each locking element including a sloping inner surface which is engageable with a corresponding sloping outer surface on at least one of the grippers so that axial displacement of the at least one locking element under fluid pressure within the annular chamber causes radial displacement of the grippers into the operative condition, axially locking the grippers to the housing and clamping the pipe end within the housing.       

   For each gripper, the gripping formation may form part of a first gripping component and the locking formation may form part of a second gripping component, wherein the first and second gripping components are displaceable relative to one another. 
   Typically, the coupling includes elastomeric seals which are operatively deformed by the grippers to seal between the pipe ends and the housing. 
   In a preferred embodiment of the invention, each locking arrangement includes an outlet for allowing fluid out of the annular chamber. 
   In a particularly preferred arrangement, a grease nipple is attached or attachable to each chamber inlet and a pressure release mechanism is attached or attachable to each chamber outlet. In this way, grease can be introduced into each of the annular chambers under pressure with a grease gun or other similar device until the pressure within each chamber reaches a predetermined magnitude, typically slightly higher than the pressure required to effect locking of the grippers to the pipe ends. 
   Each locking element may comprise a locking ring which defines a tapered inner surface for engaging the grippers. 
   The locking formation on each gripper may comprise a locking projection which is arranged to nest within a locking recess in the housing or to locate adjacent a corresponding locking projection on the housing. 
   Preferably, the housing includes an inner portion which defines an outwardly projecting rim, and the locking projections on the grippers are arranged to slide radially into locking engagement with the outwardly projecting rim. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings in which: 
       FIG. 1  shows a partially cut-away side view of a pipe coupling according to one embodiment of the present invention in an inoperative condition; 
       FIG. 2  shows an end view of the pipe coupling of the invention; 
       FIG. 3  shows a cross-sectional view along the line  3 - 3  in  FIG. 2  with the coupling in an inoperative condition; and 
       FIG. 4  shows a view similar to that of  FIG. 3  with the coupling In an operative condition. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The coupling  10  illustrated in  FIGS. 1 and 2  of the drawings is designed to join together two adjacent pipes (not shown) for conveying fluid under pressure. In the illustrated embodiment, the coupling  10  is formed from a plastics material, typically a reinforced polymer, and includes a housing  12  defining a central bore  13  for receiving the ends of the pipes, and a locking arrangement  14  at each end of the housing (only one of which is visible in the drawings). Each pipe is inserted in an axial inward direction A 1  and removed in an axial outward direction A 2 . 
   The housing  12  consists of a central body portion  16  and two end caps  18  which are threadedly engageable with the central body, as shown. Each end cap  18  includes an annular opening  20  which is alignable with an opening  22  in the body  16  to form an annular chamber  23  within the housing. 
   The reference numeral  24  designates an annular, dynamic hydraulic seal which is movable axially relative to the housing  12  in the directions of the arrows A and B. Also movable in the directions of the arrows A and B is a locking ring  26  which defines a tapered inner surface  28 . Four grippers  30  are arranged around the bore  13  so as to be movable radially within the housing in the directions of the arrows C and D. Each gripper  30  defines a sloping outer surface  32  which is designed to engage a portion of the tapered inner surface  28  on the locking ring  26 . Each gripper  30  also includes a gripping formation in the form of three sharpened ribs  36  which form teeth for gripping the end of a pipe inserted into the bore  13 , and a locking formation in the form of a projection  38  which has an axially outwardly facing surface  38   a  arranged to engage an axially inwardly facing surface  40   b  formed on a radially outwardly projecting rim  40  on an inner portion  42  of the housing  12  for axially locking the gripper to the housing. The axially outwardly facing surface  38   a  forms the axially inner end of a radially inwardly open recessed area of the locking formation which, in turn, is defined by a groove having an axially inwardly facing surface  40   b  which faces the surface  38   a  and contacts the rim  40 . A recessed portion  44  in each gripper  30  defines a seat for a circumferential, elastomeric seal  46  which is designed to seal between the pipe end and the housing, in use. 
   With particular reference to  FIG. 3  of the drawings, an inlet  48  leads into each annular chamber  23  and an outlet  50  leads out of each annular chamber. As can be seen, the coupling  10  includes a grease nipple  52 . In the inlet  48  for allowing grease to be introduced into the chamber  23  with a grease gun or other similar device (not illustrated), and a pressure release mechanism  54  in the outlet  50  for allowing grease to exit the chamber  23  when the pressure within this chamber reaches a predetermined magnitude. 
   In practice, the coupling  10  is used to join together the ends of two adjacent pipes  56 . Only one of the pipes  56  is shown in  FIG. 3 , but it will be appreciated that a similar pipe is connected to the other end of the coupling in a fashion similar to that described immediately below. 
   First, the end of one of the pipes  56  is inserted into the bore  13  so as to extend to a central region of the housing  12 , as illustrated in  FIG. 3 . A conventional grease gun (not shown) is then connected to the grease nipple  52  and actuated so as to introduce grease into the annular chamber  23  via the inlet  48 . Where it is not practical to use a grease gun, for example on relatively long pipelines, a device capable of releasing grease at a faster rate would typically be used. As the grease enters the chamber  23 , it first fills this chamber and then applies hydraulic pressure to the seal  24  so as to drive this seal and hence the locking ring  26  in the direction of the arrow A in  FIG. 3 . As the locking ring is displaced in the direction of the arrow A, its tapered surface  28  interacts with the surfaces  32  on the grippers  30  so as to drive the grippers radially inwardly in the direction of the arrows C, from an inoperative condition which is illustrated in  FIG. 3  to an operative condition which is illustrated in  FIG. 4 . In the operative condition, the locking formations  38  locate adjacent the outwardly projecting rim  40  on the inner portion  42  of the housing  12 , as shown, to axially lock the grippers to the housing, and the gripping formations  36  engage the end of the pipe  56  to clamp the pipe within the coupling. The inward movement of the grippers  30  also deforms the seal  46  to form a seal between the end of the pipe  56  and the housing  12 . 
   The pressure release mechanism  54  is designed to release grease from the chamber  23  when the pressure in the chamber reaches a predetermined pressure at which the grippers  30  are firmly clamped to the end of the pipe  56  and are locked in position by the locking ring  26 . In this condition, the locking ring is firmly wedged between the grippers  30  and the housing  12 . The friction forces between the grippers and the locking ring hold the locking ring in position so that it is not necessary to maintain the predetermined pressure within the chamber  23 . This is advantageous because the pressure can then attenuate with no adverse effect on the integrity and efficiency of the coupling. In the illustrated embodiment, the pressure release mechanism  54  includes a diaphragm or membrane (not shown) which is designed to rupture at a predetermined pressure within the annular chamber  23  so as to release pressure from this chamber once the grippers  30  have been displaced into the operative condition. 
   When the pipe  56  has been locked in the coupling  10  in the manner described above, protective covers  60  and  62  are placed over the grease nipple  52  and the pressure release mechanism  54  to protect these, in use. Thereafter, the other pipe is inserted into the opposite end of the coupling  10  so as to butt against the end of the pipe  56  and the coupling is locked to the pipe in a similar manner to that described above. 
   In another, non-illustrated embodiment of the invention, the grippers each comprise a first gripping component which includes the gripping formation and a second gripping component which includes the locking formation. In this embodiment of the invention, the first and second gripping components may be displaceable relative to one another. 
   It should be appreciated that the coupling  10  does not require complicated installation procedures and is easily installed on site, without it being necessary for a user to understand how the coupling works, by merely feeding the end of a pipe into the coupling and subsequently introducing grease into the coupling housing through the grease nipple  52  until the grease is discharged through the pressure release mechanism  54 . 
   It will also be appreciated that, when the pipe  56  is used to convey fluid under pressure, loads are transferred from the pipe  56  to the central body portion  16  of the housing  12  both via the threaded connection between the end cap  18  and the central body portion  16 , and via engagement between the locking formations  38  on the grippers  30  and the rim  40  on the central body portion  16 . Apart from distributing the load transfer into the central portion  16  of the housing  12 , by spreading the loads between the threaded portion and the rim  40  of the body portion  16 , the housing  12  is capable of resisting relatively high pull-out loads from the pressurised pipe  56 . 
   It will be appreciated further that the coupling of the invention is essentially a one-piece unit with no loose parts that can be misplaced or lost on site. Also, the fact that there are no bolts or other similar fasteners on the coupling means that the difficulties associated with the proper installation of conventional couplings with bolts, which often requires fastening in a particular manner and/or sequence, is avoided. 
   Another feature of the coupling of the invention is that it is fully end restraining thereby eliminating movement in the joint area and possible weeping of the joint over time. 
   Yet another advantage of the coupling according to the invention is that it automatically aligns the butted pipe ends so as to reduce turbulence at the joint. 
   The coupling has the further advantage of producing a uniform clamping force over the entire circumference of the pipe end which deforms out of round plastics pipe ends into circular shape.