GB2294990A

GB2294990A - Push-fit pipe fitting with grab ring

Info

Publication number: GB2294990A
Application number: GB9422834A
Authority: GB
Inventors: Robert Lyall
Original assignee: Hepworth Building Products Ltd
Current assignee: Hepworth Building Products Ltd
Priority date: 1994-11-11
Filing date: 1994-11-11
Publication date: 1996-05-15
Anticipated expiration: 2014-11-11
Also published as: GB9422834D0; AU3851595A; WO1996015403A1; GB2294990B

Abstract

A pipe fitting 1 includes a socket 2 having an axially inner grab ring 6 having circumferentially spaced teeth and an axially outer seal 5. The seal 5 and grab ring 6 are configured such that the grab ring 6 does not afford a greater resistance to spigot insertion than does the seal 5. This reduces the possibility that the resistance afforded by the grab ring 6 is mistakenly interpreted as an indication of full insertion of the spigot into the socket 2. A support ring 7 is located between the seal 5 and grab ring 6 and has a tapered surface 70 which resists flexing of the teeth of the grab ring 6 in a radially outer direction. <IMAGE>

Description

PIPE 'THING WITH GRAB RING This invention relates to a pipe fitting. More particularly, the invention relates to a pipe fitting of the type which incorporates a socket with an internal axially outer sealing ring, for providing a sea2 and an axially inner grab ring for resisting withdrawal of a pipe spigot from the socket.

The above described socket arrangement greatly facilitates the assembly of plumbing components. This is because a plastic piping spigot can simply be pushed into the socket, via the mouth and the sealing ring, and can be subsequently held in position by the grab ring. Furthermore, the pipe may be rotated within the socket, even after full insertion.

The grab ring is provided for retaining a pipe spigot within the socket and must, therefore, strongly resist withdrawal of the spigot. As a result the grab ring presents a fairly high jointing force, which is higher than that ofthe sealing ring. Consequently, a person assembling the structure might insert the spigot through the sealing ring and interpret the resistance of the grab ring as the end of the insertion path. Normally, the spigot would, despite this, have been inserted sufficiently far as to enable the grab ring to bite the very end of the spigot. This could reinforce the deduction that the spigot is fully inserted, because it is being retained in position. Furthermore, to exacerbate the situation, the joint may well function perfectly at relatively low pressures.However, upon a pressure increase, the axial force on the joint would be greater and thus could overcome the relatively minimal retention force provided by the poor connection. As a result, the connection could break and the spigot escape at least partially from the socket, impairing the seal and causing a leak.

The present invention sets out to improve the above identified known fitting by providing a socket which does not exhibit the above described disparity between the resistance to insertion afforded by a sealing ring and a grab ring. In doing this, the invention sets out to provide a socket which retains the same degree of resistance to extraction of the spigot enjoyed in known couplings.

According to the invention there is provided a pipe fitting comprising a socket which includes a sealing ring situated inside the bore of the socket at a relatively outer axial position and a grab ring located inside the bore of the socket at a relatively inner axial position; wherein the sealing ring and grab ring are configured such that the grab ring provides no more resistance to the axial insertion of a spigot into the bore of the socket, than does the sealing ring.

By limiting the resistance to insertion afforded by the grab ring and the sealing ring, the socket does not deceive the person assembling the joint into believing that the pipe is fully inserted when it is not.

Preferably, the resistance to insertion provided by the grab ring is such that it is normally overcome by the impetus of the spigot resulting from the force required to insert it through the sealing ring.

Preferably, a support ring is provided between the grab ring and sealing ring; the grab ring comprising a plurality of teeth directed radially inwardly and axially inwardly; the support ring comprising a conical surface for insertion at least partially into the grab ring in the axial direction for resisting flexion of the teeth in the axially outer direction, whilst allowing flexion of the teeth in the axially inner direction.

In a preferred embodiment, the grab ring and sealing ring provide substantially equal resistance to the insertion of a spigot. The sealing ring may be an O-ring.

According to the invention there is also provided a pipe fitting comprising a socket which includes a sealing ring situated inside the bore of the socket at a relatively outer axial position and a grab ring located inside the bore of the socket at a relatively inner axial position with a support ring therebetween; the grab ring comprising a plurality of teeth directed radially inwardly and axially inwardly; the support ring comprising a conical surface for insertion at least partially into the grab ring in the axial direction for resisting flexion ofthe teeth in the axially outer direction, whilst allowing flexion ofthe teeth in the axially inner direction; wherein the grab ring includes a circumferential spacing between each circumferentially consecutive one ofthe said teeth, the arrangement being such that the teeth can flex independently of one another.

Preferably, each consecutive tooth is separated by a circumferential spacing which, at the base ofthe tooth, is at least 40% ofthe length ofthe base ofthe tooth in the circumferential direction ofthe grab ring. In a particularly preferred embodiment, the circumferential spacing is 46% ofthe length ofthe base of each tooth.

According to the invention there is also provided a pipe fitting comprising a socket which includes a sealing ring situated inside the bore of the socket at a relatively outer axial position and a grab ring located inside the bore of the socket at a relatively inner axial position with a support ring therebetween; the grab ring comprising a plurality of teeth directed radially inwardly and axially inwardly; the support ring comprising a conical surface for insertion at least partially into the grab ring in the axial direction for resisting flexion of the teeth in the axially outer direction, whilst allowing flexion of the teeth in the axially inner direction; wherein the total length ofthe bases ofthe said teeth in the circumferential direction represents no more than 70% of the total circumferential length ofthe grab ring on a circumferential line where the bases ofthe teeth are situated.

In a particularly preferred embodiment, the total length of the bases of the teeth in the circumferential direction is 68% of the total circumferential length of the grab ring on a circumferential line where the bases of the teeth are situated.

Preferably each tooth is inclined at an angle of approximately 45" to the longitudinal axis of the grab ring. The angle of the conical surface of the support ring may also be inclined at an angle of 450 to the longitudinal axis ofthe support ruing, so as to fit closely against the teeth when the support ring lies in position next to the grab ring. In one preferred embodiment, the number of teeth provided in the grab ring is eight, however in other embodiments more or less teeth are provided. The grab ring may be made from stainless steel.

Each tooth may be defined by a root portion located towards the base of the tooth and a pair of flank portions inclined with respect to each other and extending from the tip ofthe tooth towards the root ofthe tooth. The flank portions may be inclined by an angle in the region of 140 with respect to each other. A flute, increasing in width from the root of the tooth to the tip of the tooth, may run from a point between the base ofthe tooth and the tip ofthe tooth to the tip ofthe tooth, so as to separate the two flank portions. The flute may have a part-circular cross-section.

The invention also provides a grab ring for use in any ofthe above described pipe fittings and having any or all of the features set out hereinabove.

An embodiment of the invention will now be described by way of example and with reference to the accompanying drawings in which: Figure 1 is a cross-section through a socket of a fitting in accordance with the present invention; Figure 2 is a partial plan view of the grab ring of the socket of Figure 1, also showing the profile of a conventional grab ring in dashed lines for comparison; Figure 3 is a cross-section along the line rn-rn in Figure 2; Figure 4 is a cross-section along the line IV-IV in Figure 2; Figure 5 is a plan view of an alternative embodiment of a grab ring; Figure 6 is a cross section along the line VI-VI in Figure 5; and Figure 7 is a view on VII in Figure 6.

Figure 1 shows a socket in which all of the components are known except for the grab ring 6.

The socket 1 comprises a bore 4, with a shoulder 3 and a portion 2 of enlarged diameter for receiving a pipe spigot and housing numerous components for forming a sealed joint between the socket and a spigot.

Moving axially outwardly, towards the mouth of the socket, there are provided in sequence: a grab ring 6, seated upon the shoulder 3; a retaining ring 7, seated upon the grab ring 6; an O-ring 5, seated upon the retaining ring 7; and closure means 8, 9 and 10 which are fitted in the mouth of the portion of enlarged diameter 2 for retaining the other components within the socket and for defining an insertion aperture for the spigot end. The closure components 8, 9 and 10 have no bearing on the invention and will not be described further.

The grab ring 6 comprises a number of teeth 60 arranged upon an outer portion 62 for supporting and locating the teeth 60 in the socket. The teeth are directed radially inwardly and axially inwardly when the grab ring is located in the socket. The retaining ring 7 comprises a frustoconical surface 70 which is inclined at an angle to correspond with the inclination of the teeth 60. The grab ring 6 and the retaining ring 7 co-operate in such a manner as to enable the insertion of a spigot end past the teeth, but to resist the removal of the spigot end.

The grab ring 6 is made from stainless steel, and the teeth 60, therefore, have an inherent flexibility coupled with considerable strength. As the spigot end is pushed passed the teeth 60, each tooth 60 deflects about its base 61, where it is joined to outer grab ring portion 62. If, after insertion, an extraction force is supplied to the spigot, the tips 63 of the teeth 60 bite into the radially outer surface of the spigot. Due to the angle of inclination of the teeth 60, as the force continues, the teeth bite further into the surface of the pipe spigot, thereby providing a significant resistance to withdrawal.

This resistance is reinforced by the frustoconical surface 70 of the retaining ring 7, which supports the teeth 63 and prevents them from deflecting too far.

Referring to Figure 2, it can be seen that each tooth 60 appears trapezoidal in plasm It can be seen from Figures 3 and 4, which are taken respectively along the lines m-m and IV-IV in Figure 2, that the cross-sectional shape of each tooth 60 changes from tip to base. From the tip until a peak point 64 along the length of the tooth, the crosssection is triangular, as the tooth is essentially defined by two flat flank portions 65. In a base region of the tooth, a further generally flat root portion 66 tapers from the base 61 towards the tip 63 ofthe tooth to terminate at peak point 64.

Because the support ring 62 is curved, the width ofthe root portion 66, i.e. the width of the tooth at the point where it is joined to the ring 62, will influence the flexibility of the tooth about this junction. This is a particularly effective way of controlling the flexibility ofthe teeth and, hence, resistance to insertion.

Furthermore, the length of the tooth from tip 63 to base 61 will, for a given withdrawal force, determine the turning moment about the junction of the tooth 60 with the ring 62. As a result, for a given width, a longer tooth will be easier to flex.

Depending upon the manufacturing process employed, the size of the teeth may best be controlled by the amount of material removed from between the teeth, i.e. the separation between the teeth. This will also have the effect of influencing the number of teeth which are provided. Of course, for a given tooth size, a larger number of teeth will provide a larger resistance to withdrawal. In the present example, eight teeth are provided with their centres arranged at 45" intervals around the circumference of the grab ring. Regarding size, it can be seen that, in the present embodiment, the separation between each tooth 60 is approximately 46% the base 61 width of each tooth 60 which is, in turn, just over twice the width of the tip 63 of each tooth.The length of each tooth 60 is approximately 150% that of the tip 63 of each tooth 60 and the distance from the peak point 64 of each tooth to its tip 63 is just slightly larger than the width of the tip 63. The teeth, where they join the ring 62, account for 68% of the circumference of the ring. The remaining 32% being defined by the intermediate spaces.

The flexibility of each tooth will also be influenced by its angle of inclination with regard to the axis of the grab ring. This can therefore be controlled to influence the flexibility of the tooth and, therefore, the resistance to insertion and withdrawal afforded by the tooth.

The above relative parameters can be maintained whilst increasing the number of teeth.

Thus different rings of different diameters can have teeth of the same size but in differing numbers.

Accordingly, by selecting the size, shape, inclination and number of teeth, teeth with a specified flexibility, for a given material, can easily be provided.

The above discussed parameters are controlled in such a fashion that the grab ring resists insertion of the spigot in a manner which more or less exactly corresponds with the resistance afforded by the 0-ring 5. For example in one test of a socket for receiving a 15mm spigot, each of the grab ring and the O-ring independently offered a jointing force of 8kg. As a result, when a spigot is inserted past the O-ring and the grab ring, the resistance will appear uniform and the first increase in resistance will arise when spigot is fully inserted into the socket. This will ensure that the person assembling the joint will not be deceived into thinking that the pipe is filly inserted when it is not. This effect is realised because the insertion force is used to introduce a strain in the O-ring (to deform it) and also to overcome its frictional resistance. As a result, initially the applied force does not cause significant axial movement of the spigot into the socket. However, as this 'sticking' condition is overcome and the spigot slips through the ring, the force applied to enable this has reached such a level that the impetus of the spigot carries it on through the grab ring with no detectable additional resistance.

Figure 5 shows an alternative embodiment of a grab ring. This grab ring can equally be employed in the fitting shown in Figure 1.

It will be seen from Figure 5 that each tooth 60 is, like the tooth 60 in the grab ring of Figure 2, generally trapezoidal when viewed in plan. Like the earlier embodiment, this grab ring also comprises eight teeth arranged with their centres at 45" intervals. The profile of these teeth, when viewed in plan, generally similar to that of the grab ring in Figure 2. The major difference between the teeth of the grab ring of Figure 5 and the grab ring of Figure 2 is that each tooth in the grab ring of Figure 5 includes a flute 68, which extends from the tip 63 ofthe tooth towards the peak point 64.

As can clearly be seen from Figure 7, the flank portions 65 of the tooth are inclined at an angle of 1400 to each other. In addition, each tooth is inclined at an angle of approximately 45" to the longitudinal axis of the grab ring.

Many further modifications and variations will suggest themselves to those versed in the art upon making reference to the foregoing illustrative embodiment, which is given by way of example only, and which is not intended to limit the scope ofthe invention which is determined solely by the appended claims.

Claims

1. A pipe fitting comprising a socket which includes a sealing ring situated inside the bore of the socket at a relatively outer axial position and a grab ring located inside the bore of the socket at a relatively inner axial position; wherein the sealing ring and grab ring are configured such that the grab ring provides no more resistance to the axial insertion of a spigot into the bore of the socket, than does the sealing ring.

2. A pipe fitting according to claim 1, wherein the sealing ring is an O-ring.

3. A pipe fitting according to any preceding claim, wherein the grab ring and sealing ring provide substantially equal resistance to the insertion of a spigot.

4. A pipe fitting according to any preceding claim, wherein the resistance to insertion provided by the grab ring is such that it is normally overcome by the impetus of the spigot resulting from the force required to insert it through the sealing ring

5. A pipe fitting according to any preceding claim, wherein a support ring is provided between the grab ring and sealing ring; the grab ring comprising a plurality of teeth directed radially inwardly and axially inwardly; the support ring comprising a conical surface for insertion at least partially into the grab ring in the axial direction for resisting flexion of the teeth in the axially outer direction, whilst allowing flexion of the teeth in the axially inner direction.

6. A pipe fitting according to claim 5, wherein the grab ring includes a circumferential spacing between each circumferentially consecutive one of the said teeth, the arrangement being such that the teeth can flex independently of one another.

7. A pipe fitting according to claim 6, wherein each consecutive tooth is separated by a circumferential spacing which, at the base of the tooth, is at least 40% of the length of the base of the tooth in the circumferential direction of the grab ring.

8. A pipe fitting according to claim 7, wherein the circumferential spacing is 46% of the length of the base of each tooth.

9. A pipe fitting according to any one of claims 5 to 8, wherein the total length of the bases of the said teeth in the circumferential direction represents no more than 70% of the total circumferential length of the grab ring on a circumferential line where the bases of the teeth are situated.

10. A pipe fitting according to claim 9, wherein the total length of the bases of the teeth in the circumferential direction is 68% of the total circumferential length of the grab ring on a circumferential line where the bases of the teeth are situated.

11. A pipe fitting according to any one of claims 5 to 10, wherein each tooth is inclined at an angle of approximately 45" to the longitudinal axis of the grab ring.

12. A pipe fitting according to claim 11, wherein the angle of the conical surface of the support ring is also inclined at an angle of 450 to the longitudinal axis of the support ring, so as to fit closely against the teeth when the support ring lies in position next to the grab ring.

13. A pipe fitting according to any one of claims 5 to 12, wherein the number of teeth provided on the grab ring is eight.

14. A pipe fitting according to any preceding claim, wherein the grab ring is made from stainless steel.

15. A pipe fitting according to claim 5 or any claim dependent on claim 5, wherein each tooth comprises a root portion located towards the base of the tooth and a pair of flank portions inclined with respect to each other and extending from the tip of the tooth towards the root of the tooth.

16. A pipe fitting according to claim 15, wherein the flank portions are inclined by an angle in the region of 140 with respect to each other.

17. A pipe fitting according to claim 15 or 16, wherein a flute, increasing in width from the root of the tooth to the tip of the tooth, runs from a point between the base of the tooth and the tip of the tooth to the tip of the tooth, so as to separate the two flank portions.

18. A pipe fitting according to claim 17, wherein the flute has a part-circular crosssection.

19. A pipe fitting substantially as hereinbefore described with reference to any one of the accompanying drawings.

20. A grab ring for use in a pipe fitting according to any preceding claim and comprising the features of the grab ring specified in that claim.

21. A grab ring substantially as hereinbefore described with reference to any one of the accompanying drawings.