Pipe fitting

[0001] This is the U.S. national stage application which claims priority under 35 U.S.C. §371 to International Patent Application No.: PCT/ZA2011/000020 filed on Jul. 7, 2011, which claims priority to South African Patent Application No. 2010/04923 filed on Jul. 13, 2010, the disclosures of which are incorporated by reference herein their entireties.

[0002] This invention relates to a pipe coupling and in particular a push-fit compression fitting.

[0003] Prior art pipe fittings are available which act as either compression fittings or push-fit fittings, but not both.

[0004] For example, JP 2001074178 (Bridgestone Corp), which aims to reduce the number of parts constituting a pipe joint, is a push-fit fitting but is not a compression fitting. This fitting includes a grip ring (1) which comprises a cylinder/ring made of resin, with a number of metallic claws or teeth embedded in the ring such that the tips of the teeth protrude to engage the pipe that is fitted. A cap (15) screws onto the pipe body (11) but does not act on the grip ring (1). The cap simply retains the O-ring in place and prevents it from moving under pressure, but does not compress the O-ring and therefore does not act as a compression fitting. This is clear from FIGS. 5, 6 and 7 of the patent.

[0005] CN 201237049 (PRIORITY DATE Oct. 7, 2008)

[0006] This is a utility model (registered design) for a quick pipe joint for a compressed air pipe. The pipe joint comprises a joint pipe (1) (see drawings) and a press cover (2) detachably connected to the joint pipe by means of a screw thread. A clamp ring base (5) is arranged on the head section of the joint pipe. The inner end of the clamp ring (5) protrudes into the joint pipe. A sealing ring (4) abuts against the clamp ring base (5). The inner ring of the sealing ring protrudes (stands proud) out of the inner diameter of the clamp ring base. A metal elastic clamp ring (6) is arranged at the outer end face of the clamp ring base (5) and includes a ring body and claw teeth folded in the direction of the clamp ring base. A bevel ring is arranged at the opening of the clamp ring base and the claw teeth about the bevel ring. A pusher (7) abuts the outer end of the elastic clamp ring and a boss (on the press cover 2) abuts the other end of the pusher.

[0007] In use, the press cover (2) is screwed tightly and the boss on the press cover causes the pusher to drive the elastic clamp ring (6) against the bevel ring, causing the teeth to “expand” and clamp the pipe.

[0008] Although the pusher acts against the clamp ring to expand the teeth and clamp the pipe, and therefore allows it to act as a push-fit fitting, it does not engage the O-ring at all. This is clear from FIG. 1 that the clamp ring base 5 engages and abuts against the end of the joint pipe 1 which prevents the clamp ring base acting upon the O-ring 4. Accordingly, and although the O-ring may protrude into the inner diameter of the clamp ring base, it simply acts as a seal and is not compressed about the compressed air pipe. The fitting of CN 201237049 therefore is a push-fit fitting but not a compression fitting or a push-fit compression fitting.

[0009] It is an object of this invention to provide a push-fit pipe coupling which has the additional advantage of including a nut which may be tightened thereover to provide additional gripping force and better sealing.

[0010] According to the invention, a push-fit compression pipe fitting comprises a body defining one or more socket for receiving an end of a pipe, the socket being encircled by a threaded face; and being internally adapted to receive a compressible O-ring; a clamping nut which can be screwed onto the threaded face, and a grip ring; the nut having an internal tapered surface and the grip ring having a complimentally tapered surface which when the nut is tightened onto the threaded face, bears upon the grip ring compressing it against the pipe and compressing the O-ring sealing means located within the socket against the pipe.

[0011] The socket includes a circumferential recess about the mouth thereof which acts as an O-ring seat; and a rear shoulder or flange or step.

[0012] The grip ring preferably comprises a split ring which preferably has an internal diameter which is slightly smaller than the external diameter of the inserted pipe, which results in the grip ring expanding slightly when the pipe is inserted therethrough. The grip ring further includes a plurality of small teeth spaced apart about the internal or pipe engaging surface thereof. In the preferred form, the grip ring comprises a stainless steel ring embedded within a plastic composite material. The stainless steel ring includes about its internal diameter, one or more teeth angled inwardly and in the direction of the fitting body when the fitting is assembled.

[0013] The underside of the grip ring is dimensioned to engage the mouth of the socket, and may include a ridge or the like protruding formation defining a stepped surface adapted to engage the O-ring, the ridge being spaced apart from the external diameter of the grip ring to fit within the O-ring seat and linearly compress the washer and O-ring, against the O-ring seat, causing the O-ring to be deformed and in so doing tightly engaging the inserted pipe end. The ridge may be eliminated by providing an o-ring having a larger cross sectional diameter.

[0014] In the preferred form of the invention, a flat washer may be provided between the O-ring and the grip ring. The washer may be omitted, as described above with the grip ring engaging the O-ring directly, but the fitting has been found to perform better under extreme pressure conditions if the washer is present, as it prevents damage to the O-ring caused by the ends of the split ring under these conditions.

[0015] Because the internal diameter of the grip ring is smaller than that of the external diameter of the inserted pipe, the fitting acts as a push-fit compression fitting, expanding the grip ring as it pushes therethrough with the result that full tightening of the clamping nut may not be required. However, when the clamping nut is tightened, there is a force opposing that exerted by the nut on the grip ring, which results in a tight engagement between not only the pipe and grip ring, but especially between the O-ring and the pipe. This is particularly useful where the pipe is scratched or damaged and additional compression is required.

[0016] Thus it is the grip-ring which prevents the pipe from being pulled out of the fitting, but it is the O-ring which provides significant compression resulting in a unique push-fit compression fitting.

[0028] In FIGS. 1 to 4, a pipe fitting or coupling 10 comprises a body 12, a clamping nut 14, a grip ring 16 and a washer 18 and an O-ring 20.

[0029] The body 12 includes a socket at each end for receiving a pipe 22 and the socket includes a widened recess 24 which acts as a seat for the washer 18 and O-ring 20. Externally, the socket is threaded (FIG. 2) to receive the clamping nut 14. Opposing sockets are separated by a flange 26 or step 26.

[0030] The clamping nut 14 has an internal tapered surface 28 for engaging and bearing upon the complimentally tapered surface 30 of the grip ring 16.

[0031] The washer 18 is flat and comprises metal while the O-ring 20 comprises a resiliently deformable material, for example rubber or silicone rubber.

[0032] Turning now to FIGS. 5 through 7, the grip ring 16 is shown to be moulded from plastic and includes embedded therein, a stainless steel split ring 32 as shown in FIGS. 8 to 10. The underside of the grip ring has a diameter sufficiently large to span the mouth of the socket and abut surface 34. The underside of the grip ring is further stepped or ridged 36 at an external diameter dimensioned to fit within the recess or O-ring seat 24. This enables the ridge or step 36 to engage the washer 28 and exert a linear force onto the washer 18 and in turn, the O-ring 20 when the clamping nut 14 is tightened.

[0033] The split ring 32 has teeth or the like protrusions 38 about its internal diameter, which are directed inwardly and in the direction of insertion of the pipe. Formations 40 and 42 assist in stabilising the stainless steel ring within the mould during moulding of the grip ring 16.

[0034] In use, the fitting of the invention is pre-assembled with the clamping nut partially threaded onto the body, and the grip ring in loose abutment with both the internal tapered surface of the clamping nut and the mouth 34 of the body. A pipe end is then pushed into the fitting, causing expansion of the split grip ring into firm abutment with the tapered surface of the nut and the mouth 34 of the body. This in turn causes linear compression of the O-ring which deforms to tightly engage the pipe (as shown in FIG. 2). If additional compression is required, the nut may be advanced by rotation on the threaded face of the body to apply additional pressure on the grip ring and the O-ring.