GB2321685A

GB2321685A - Pipe coupling having a grab ring

Info

Publication number: GB2321685A
Application number: GB9702131A
Authority: GB
Inventors: Michael Taylor
Original assignee: POLYPIPE PLC
Current assignee: POLYPIPE PLC
Priority date: 1997-02-03
Filing date: 1997-02-03
Publication date: 1998-08-05
Anticipated expiration: 2017-02-03
Also published as: GB9702131D0; GB2321685B

Abstract

The coupling 1 comprises the grab ring 2, with a plurality of teeth 3 flexibly attached to a skirt part 4, and an element 5 adapted to substantially prevent movement of the teeth 3 upon the application of a tensile load to a pipe 6 inserted in the coupling. The element 5 is a ring with an arcuate or V radial cross-section, conforming to the cross-section of the ring 2 where its teeth 3 join the skirt 4.

Description

A PIPE COUPLING The present invention relates to a pipe coupling, and to a set of parts for inclusion in a pipe coupling.

Pipe couplings are known which employ toothed retaining rings, also referred to as grab rings, which help to keep an inserted pipe securely in the coupling. Their general construction includes a ring of inwardly projecting inclined teeth flexibly and resiliently hinged to a supporting skirt. When deflected the teeth have a tendency to return to their former positions.

The diameter of the circle formed by the free ends of the teeth is less than the diameter of the pipe which the ring is designed to fit. When the pipe is inserted through the ring, the teeth are deflected at their free ends and forced to hinge at the fixed end by bending the material at the tooth root. The free ends of the teeth maintain a contact force on the pipe diameter, ring diameter, tooth length and ring material.

If an attempt is made to withdraw the pipe, the teeth tend to dig into it and resist the force tending to pull it out. Under these conditions the pipe end load is transferred to the skirt of the ring via the teeth, which behave as struts in axial compression. If the end load is increased sufficiently, one or more teeth may fail by, for example, buckling. This is especially so where the toothed ring is manufactured from thin sheet material and the resulting teeth have a low resistance to failure by buckling in compression.

It is an object of th?e present invention to try to mitigate problems such as this.

According to the invention there is provided a pipe coupling comprising a grab ring including a plurality of teeth flexibly attached to a skirt part, and an element adapted substantially to prevent movement of the teeth upon the application of a load to a pipe in use.

The element may comprise a ring having an arcuate or V-shaped radial cross section, adapted in use to receive therein the point of attachment of the teeth to the skirt of the grab ring.

It is preferred that one of the arms of the arc or V is longer than the other.

It is most preferred that the outer arm of the arc or V is longer than the inner arm. The outer arm may extend in use substantially parallel to the skirt of the grab ring.

The teeth of the grab ring may include strengthening means. The strengthening means may comprise a flange extending from a longitudinal edge of each tooth.

The element may comprise a metal, and may be integrally formed therefrom.

According to a second aspect of the invention there is provided a set of parts for inclusion in a pipe coupling, comprising a grab ring including a plurality of teeth flexibly attached to a skirt part and an element adapted substantially to prevent movement of the teeth upon the application of a load to a pipe installed in the coupling.

The invention will further be described by way of example only, with reference to the accompanying drawings, in which Fig. 1 is a schematic drawing of half a radial cross section of a pipe coupling according to the prior art; Fig. 2 is a schematic drawing of half of a radial cross section of a pipe coupling embodying the invention.

Fig. 3 is a front view of a grab ring; Fig. 4 is a sectional view of the grab ring of fig. 3 along line R-R; and Fig. 5 is a view of a tooth of the grab ring of fig. 3.

Referring to the drawings there is illustrated a pipe coupling 1 comprising a grab ring 2 including a plurality of teeth 3 flexibly attached to a skirt part 4, and an element 5 adapted to substantially prevent movement of the teeth 3 upon the application of for example a tensile load to a pipe 6 inserted in the coupling.

The grab ring 2 consists of a ring or washer, the inner circumference of which is provided with a series of teeth 3 projecting inwardly from it. The teeth 3 may be formed as an integral part of the ring 2 by any suitable means. Each tooth has a substantially planar body part 7 from which two flanges 8 project at substantially 90".

A spacer washer 9 is placed next to the grab ring 2 in the coupling 1 between the grab ring 2 and an 'O' ring seal 10. A retaining cap (not shown) is fitted to the coupling which bears directly on the washer. The cap is usually fixed to the body 11 of the coupling 1 by means of a screw thread (not shown), which allows the cap to compress the washer, forming a seal around the pipe 6.

Referring to figure 2 the coupling 1 includes an element 5 adapted to obviate movement of the teeth 3 upon the application of a tensile load to the pipe 6.

The element 5 comprises a ring or washer having an arcuate radial cross section as shown at "X" in figure 2. As can be seen, the outer circumference 12 of the element 5 is longer than the inner circumference 13, extending downwardly beyond it, as viewed. The element 5 is conveniently integrally formed from, for example, a metal.

In use, the element 5 substantially prevents movement of the teeth 3 of the grab ring 2 upon the application of a tensile load to a pipe 6 inserted in the coupling. Referring to the prior art construction shown in figure 1, the element 5 is absent. The grab ring tooth 3 is shown partially embedded in the pipe wall as a result of the application of an axial tensile load. This load is resisted by the end cap (not shown), to which it is transferred via the spacer washer 9 and the seal 10. As the load is increased further, the grab ring tooth 3 is deflected by rotation about point 'A', causing the tooth 3 to embed further into the pipe wall. Ultimately the grab ring 2 would be turned inside out and all grip would be lost.

Referring to figure 2, the element 5 is interposed between the grab ring 2 and spacer washer 9, such that the arcuate part 14 of the grab ring 2 where the teeth 3 meet the skirt 4 "nests" in the arcuate part 16 of the element 5. A sirnilar situation will apply where the grab ring 2 and element 5 have "V"shaped parts, rather than arcuate parts. It will be noted that the outer circumference 12 extends some distance down the skirt 4 of the grab ring 2 and that a small gap 16 is allowed between the tooth 3 and inner circumference 13 of the element 5.

With the element 5 in position in the coupling 1, it performs two main functions: 1) As the force is increased and tooth rotation proceeds ultimately the tooth 3 is brought into contact with the lower surface of the element 5. This effectively prevents further rotation about 'A'.

2) When subjected to tensile load, the pipe induces a compressive load in the grab ring tooth 3 acting along the axis of the individual tooth (shown by the arrow Z). This force is transferred to the skirt 15 of the grab ring 2 and results in a hoop stress around the grab ring skirt 15. This will cause deflection of the top of the skirt which allows each individual tooth root to move away from the pipe surface. This allows each tooth 3 to rotate about 'A' more easily. The presence of the element 5 reduces or eliminates this deflection and prevents premature failure.

Claims

CLAIMS:

1. A pipe coupling, comprising a grab ring including a plurality of teeth flexibly attached to a skirt part, and an element adapted substantially to prevent movement of the teeth upon the application of a load to a pipe in use.

2. A pipe coupling according to claim 1, the element comprising a ring having an arcuate radial cross section for receiving the point of attachment of the teeth to the skirt of the grab ring.

3. A pipe coupling according to claim 1, the element comprising a ring having a V-shaped radial cross section, for receiving the point of attachment of the teeth to the skirt of the grab ring.

4. A pipe couplig according to claim 2 or claim 3, wherein one of the arms of the arc or V is longer than the other.

5. A pipe coupling according to claim 2 or claim 3, wherein the outer arm of the arc or V is longer than the inner arm.

6. A coupling according to any of claims 2 to 5, in which the outer arm extends, in use, substantially parallel to the skirt of the grab ring.

7. A pipe coupling according to any preceding claim, the teeth of the grab ring including strengthening means.

8. A pipe coupling according to claim 7, the strengthening means comprising a flange extending from a longitudinal edge of each tooth.

9. A pipe coupling according to any preceding claim, the element comprising a metal.

10. A pipe coupling according to any preceding claim wherein the element is integrally formed.

11. A set of parts for inclusion in a pipe coupling, comprising a grab ring including a plurality of teeth flexibly attached to a shirt part and an element adapted substantially to prevent movement of the teeth upon application of a load to a pipe installed in the coupling.

12. A pipe coupling, substantially as hereinbefore described with reference to the accompanying drawings.

13. A set of parts, substantially as hereinbefore described with reference to the accompanying drawings.