GB2378993A

GB2378993A - Push-fit pipe coupling

Info

Publication number: GB2378993A
Application number: GB0120227A
Authority: GB
Inventors: Stephen Currid
Original assignee: Hepworth Building Products Ltd
Current assignee: Hepworth Building Products Ltd
Priority date: 2001-08-20
Filing date: 2001-08-20
Publication date: 2003-02-26
Anticipated expiration: 2021-08-20
Also published as: GB0120227D0; GB2378993B

Abstract

A pipe fitting 2 comprises a socket defined by a mouth and a bore 9, the said bore containing an annular retaining element 6 for retaining a pipe portion within the socket and an annular seal 5 for sealing between the socket and pipe portion. The bore 9 comprises a first, inclined, radially inwardly directed camming surface 12 and the retaining element 6 comprises a second, inclined radially outwardly directed camming surface 10 on a radially outer portion thereof. The arrangement is such that axial movement of the retaining element 6 from a relatively axially inner position to a relatively axially outer position causes the said second camming surface 10 to bear against and cam over the said first camming surface 12 in such a manner as to cause radial contraction of the retaining element 6, thereby serving to apply an increased gripping force upon the pipe. The fitting further comprises a washer 20, configured to limit radial expansion of the retaining element 6 if it is fitted into the socket with a reverse axial orientation.

Description

PIPE FITTING AND WASHER FOR USE IN A PIPE FITTING The present invention relates to a push-fit pipe fitting and a washer for use in such a fitting.

Push-fit pipe fittings are commonly used in various plumbing applications and have the advantage that few or no tools are required to form a joint between the fitting and any pipe which is received in a socket provided on the fitting. Such fittings are generally very well known.

Figure 1 of the accompanying drawings shows a partial sectional view through a known fitting and pipe, together forming a joint.

The pipe 1 end is inserted into the bore 9 of a socket of the fitting 2 until an end stop 4 is reached. Inside the socket, a grab wedge 6 acts as a gripping part, and takes the form of a collet through which the pipe 1 is inserted as it is pushed into the fitting. The grab wedge 6 comprises radially inwardly directed teeth 8, each tooth 8 being situated on a radially inwardly facing surface of a respective finger 7. An elastomeric O-ring seal is also situated inside the bore 9 at a position that is axially inside, relative to the grab wedge 6. The O-ring seal 5 is of such a configuration that it is compressed, in the radial direction, between a radially inner surface of the bore wall and a radially outer surface of the pipe wall, so as to form a seal between the two.

The fitting body may be made from a large range of materials. In practice the appropriate material to be used will be determined by the characteristics of the fluid to be conveyed by the fitting, the environment in which it is to be used and the forces to which it could be subjected. A large variety of metals could be used, with the most popular being brass, stainless steel and various alloys. Various types of plastics materials are also extremely popular and most polymers can be used. The most common choices are: polybutylene, polypropylene and polyethylene. Nylon, PVC,

ABS and polystyrene would also be appropriate choices in certain circumstances. The grab wedge 6 needs to be both resilient and tough and these somewhat conflicting requirements tend to reduce the range of materials available for its manufacture.

However, polysulphone and PPSU are typical, along with polyethylene and polypropylene. The radially inwardly directed teeth are usually formed from metal inserts, with stainless steel being by far the preferred material.

If a destructive axial force Fr is applied to the pipe 1 and tends to urge it out of the fitting 2, a radially outer camming surface 10 provided on the grab wedge 6 co-operates with a complementary camming surface 12 situated in the mouth of the socket. As the force Fr is applied to the pipe 1, the grab wedge 6 moves with the pipe, due to the action of the teeth 8. As a result of this movement and the consequent interaction of the camming surfaces 10,12, a radial closing force is applied to the grab wedge 6. This closing force serves to embed the teeth 8 more firmly into the pipe 1 and thus grip the pipe ever more securely. Eventually, the two camming surfaces wedge together and, in combination with the teeth 8, prevent any further axial displacement of the pipe from the socket.

The camming surface 10 in the mouth of the fitting is defined by a cap 3 which is screwed onto the main body of the fitting 2. This arrangement has a number of advantages. First, assembly during manufacture is facilitated, since the 0-rings and grab wedge 6 can be manually inserted into the bore 9 and the cap 3 then screwed-on by hand. Furthermore, once the fitting 2 has been used to make a joint with a pipe as described above, the cap 3 can be unscrewed from the fitting 2, thereby enabling the body of the fitting 2 and the 0-rings to be moved to the right, as seen in Figure 1, thereby providing access to the grab wedge 6, which can be demounted using a tool (not shown). This demounting procedure essentially enables non destructive disassembly of the joint, thereby allowing the fitting 2 to be used again.

Whilst this type of fitting has been found to be extremely effective and met with significant commercial success, it has been identified that some users occasionally insert the grab wedge 8 into the fitting in a back-to-front fashion, as shown in Figure 2.

This leads to a malfunction of the fitting, for reasons which will now be described with reference to Figures 2 and 3.

As will be seen from Figure 3, the collet design of the grab wedge 6 renders it unidirectional in that the fingers 7 are mounted upon an annular base which is not susceptible to radial compression. Hence, once it has been incorrectly inserted into the fitting in the manner of Figure 2, although insertion of the pipe could cause radial displacement of the fingers, the axial force Fr would not cause contraction of the grab wedge 6, due to the fact that the end of the grab wedge addressing the camming surface 10 is in the form of a non-compressible solid ring. This means that the wedging action described above does not take place and the pipe can easily come out of the fitting socket, thereby breaking the joint.

A similar or identical problem arises with other uni-directional gripping mechanisms, which are not necessarily collet-based.

The present invention sets out to address the above problems, by providing a fitting in which such an ineffective jointing operation cannot take place.

According to a first aspect of the invention there is provided a pipe fitting comprising a socket for receiving a pipe portion, the said socket comprising a mouth and a bore, the said bore containing an annular retaining element for retaining the pipe portion within the socket and an annular seal for sealing between the socket and pipe portion; wherein the bore comprises a first, inclined, radially inwardly directed camming surface and the said retaining element comprises a second, inclined radially outwardly directed camming surface on a radially outer portion thereof, the arrangement being such that, in normal use, axial movement of the retaining element from a relatively axially inner position to a relatively axially outer position causes the said second camming surface to bear against and cam over the said first camming surface in such a manner as to cause radial contraction of at least a part of the said retaining element, thereby serving to apply a gripping force to a said pipe portion located within the said socket; the said pipe fitting being characterised in that it further comprises a washer, the said washer being

configured to limit radial expansion of the said retaining element if the said retaining element is fitted into the said socket with a reverse axial orientation.

By limiting the radial expansion of the retaining element in this manner, the insertion of a pipe can be prevented if the retaining element is incorrectly installed in the fitting; hence an ineffective joint cannot be made.

Preferably the said washer comprises a tubular portion for surrounding at least part of the said retaining element. Such an embodiment is particularly beneficial, although not limited, for use with a collet-type retaining element.

The tubular portion may comprise an inclined, third camming surface which is radially inwardly directed and acts, in co-operation with the said second camming surface, to cause radial contraction of the said retaining element if it is fitted into the said socket with a reverse axial orientation and urged axially into the said socket away from the said mouth.

The said washer may be symmetrical about an axially facing plane bisecting the washer.

The said washer may comprise a radially inwardly directed flange.

According to a further aspect of the invention there is provided a said washer according to the first aspect of the invention.

An embodiment of the invention will now be described, by way of example, and with reference to the accompanying drawings in which :- Figure I is a cross-sectional part-view of a pipe fitting and coupling in accordance with the prior art; Figure 2 is a view corresponding to Figure 1, in which a grab wedge has been improperly installed within the fitting;

Figure 3 is a perspective view of the grab wedge forming part of the fitting of Figures 1 and 2; Figure 4 is a view corresponding to Figure 1, but showing an embodiment of the invention; Figure 5 is a view corresponding to Figure 2, but showing the embodiment of the invention shown in Figure 4; and Figure 6 is a cross-section through the washer of the fitting shown in Figures 4 and 5.

In broadly conceptual terms, the described embodiment of the invention, which is shown in Figures 3 to 6, is identical to the fitting of Figures 1 and 2. Consequently, like components will be given like reference numerals and their description will not be repeated. The embodiment is, however, different in that it comprises an additional component, namely the washer 20.

The cross-sectional profile of the washer is best viewed in Figure 6, where it will be seen that it is essentially formed from a short length of tube 22 integrally formed with a radially inwardly directed flange 24 extending from an axially central region of the tube 22. The radially inner surfaces of the tube 22 that are not defined by the flange 24 take the form of two sloped radially inner walls 28, one extending on either side of the flange 24, so that the thickness of the tube wall increases from each axial end towards an axially central region.

The axial length of the tube section 22 is such as to fit comfortably between the O-ring 5 and the grab wedge 6 and allow sufficient axially inward displacement of the grab wedge to enable the cap 3 to be mounted onto the body of the fitting 2. Indeed, it is a primary object of the washer 20 to leave the operation of the fitting totally unaffected when the fitting has been assembled properly, with the grab wedge 6 in its correct orientation (as in Figure 4).

Figure 5 shows the situation in which the grab wedge 6 has been inserted into the fitting 2 in the reverse axial orientation. From Figure 5, it will be immediately apparent that the camming surfaces 10 of the grab wedge 6 abut the adjacent sloped radially inner wall 28 of the washer 20. The washer therefore serves to constrain the fingers 7 of the grab wedge 6 from radially outward displacement.

The effect of the radial constraint of the washer 20 upon the fingers 7 of the grab wedge 6 is that a pipe end cannot be pushed into the fitting 2 past the teeth 8 of the grab wedge 6. This is because the grab wedge 6 cannot flex radially outwardly to accommodate the pipe in the manner that it does in normal usage. In fact, due to the inclined nature of the radially inner walls 28 of the washer 20, the more that a pipe is urged against the teeth 8 of the grab wedge 6, the more firmly it resists insertion, due to a slight radial contraction caused by the camming surfaces 10 camming over walls 28.

Thus the washer 20 prevents a pipe from being jointed with the fitting 2 when the grab wedge 6 has been incorrectly installed. Because the joint cannot be made in the first place, there is no danger that an ineffective joint could be formed.

The washer 20 is symmetrical about an axially-facing plane bisecting the flange 24.

This plane is shown as p-p'in figure 6. This symmetrical nature of the washer 20 ensures that it will always work, regardless of which way it is inserted into the socket.

Despite this the washer 20 could, if preferred, be provided with only a single wall corresponding to the radially inner walls 28. In such a case, the washer would have an "L"-shaped cross-section, rather than a"T"-shaped cross-section. However, this would generally be much less preferred, since it might then be possible to install the washer in the reverse orientation, thereby removing its effectiveness against reverse orientation of the grab wedge 6. Other formations could be provided on the washer 20 to prevent such reverse orientation, but the particular configuration shown in Figures 5 and 6 is the preferred solution to this problem.

The washer in the above-described embodiment of the invention may be formed from a wide range of materials. It essentially has to be stiff to react with the wedge, but thin enough to fit in the arrangement of components, so most metals would be a good choice

with stainless steel and brass being preferred. Families of plastics that have similar properties are also suitable. Typically, any stiff or resilient polymeric material could be used, but the following have been found particularly effective: polyamide, polysulphone, polyphenylsulphone (PPSU), polyphthalamide, polyvinylidenefluoride and acetyl.

Many modifications and variations will suggest themselves to those versed in the art upon making reference to the foregoing illustrative embodiments, which are given by way of example only and are not intended to limit the scope of protection, than being determined by the appended claims.

Claims

CLAIMS:

1. A pipe fitting comprising a socket for receiving a pipe portion, the said socket comprising a mouth and a bore, the said bore containing an annular retaining element for retaining the pipe portion within the socket and an annular seal for sealing between the socket and pipe portion; wherein the bore comprises a first, inclined, radially inwardly directed camming surface and the said retaining element comprises a second, inclined radially outwardly directed camming surface on a radially outer portion thereof, the arrangement being such that in normal use, axial movement of the retaining element from a relatively axially inner position to a relatively axially outer position causes the said second camming surface to bear against and cam over the said first camming surface in such a manner as to cause radial contraction of at least part of the said retaining element, thereby serving to apply gripping force to a said pipe portion located within the said socket; the said pipe fitting being characterised in that it further comprises a washer, the said washer being configured to limit radial expansion of the said retaining element if the said retaining element is fitted into the said socket with a reverse axial orientation.

2. A pipe-fitting according to Claim I wherein the said washer comprises a tubular portion for surrounding at least part of the said retaining element.

3. A pipe-fitting according to Claim 2, wherein the tubular portion comprises an inclined, third camming surface which is radially inwardly directed and acts, in cooperation with the said second camming surface, to cause radial contraction of the said retaining element if it is fitted into the said socket with the said reverse axial orientation and urged axially into the said socket away from the said mouth.

4. A pipe fitting according to any preceding claim, wherein the said washer is symmetrical about an axially facing plane bisecting the washer.

5. A pipe-fitting according to any preceding claim, wherein the said washer comprises a radially inwardly directed flange.

6. A pipe-fitting substantially as hereinbefore described with reference to Figures 4 to 6 of the accompanying drawings.

7. A said washer according to any preceding claim.

8. A washer substantially as hereinbefore described with reference to figures 4 to 6 of the accompanying drawings.