GB2258895A

GB2258895A - Compression pipe coupling

Info

Publication number: GB2258895A
Application number: GB9117799A
Authority: GB
Inventors: Paul John Hensman; John James Kelly
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1991-08-17
Filing date: 1991-08-17
Publication date: 1993-02-24
Anticipated expiration: 2011-08-17
Also published as: GB9117799D0; GB2258895B

Abstract

A pipe coupling for connecting a pipe 20 to a pipe connector sleeve 30 has an internally screw-threaded nut 110 engageable with externally screw-threaded sleeve 32 on connector sleeve 30. The nut 110 has a frusto-conical region 116 which engages with an external frusto-conical surface 22 of an axially split collet 18. The collet 18 serves to locate a seal back-up washer 28 which cooperates with an O-ring seal 28. The nut 110 has a substantially radially inwardly directed annular lip 140 providing one part of an abutment means whose other part is provided by the frustum 142 of collet 18 so as to limit the radially outward force applied to the nut 110 when extreme pressures are applied to the pipe coupling. <IMAGE>

Description

PIPE COUPLING This invention relates to a pipe coupling for sealingly securing an end of a pipe in a bore of an externally screw-threaded sleeve on another part such as a pipe connector body, a valve body, a tap body, a pump body, a piston and cylinder device, a fluid motor body or a manifold. The present invention is more particularly concerned with a collet-type pipe coupling wherein (a) a nut has an internally screw-threaded end region for engagement with the externally screw-threaded sleeve and an internal frusto-conical surface region which flares outwardly in the direction of the screw-threaded end region; and wherein (b) an axially split collet is engageable in the nut and over the pipe and has an external frusto-conical surface cooperating with the internal frusto-conical surface region of the nut.When the nut is tightened on the screw-threaded sleeve, the internal frusto-conical surface region in the nut acts on the frusto-conical surface on the collet to compress the latter inwardly so that it bites into the external surface of the pipe to hold it firmly in position. It is usual to provide a separate O-ring seal which is disposed in the bore of the screw-threaded sleeve and which seals against the pipe. A so-called seal back-up washer is also provided between the O-ring seal and the collet to prevent displacement of the O-ring seal when subjected to high service pressures, and to provide a location for the collet.

With these known pipe couplings, pressures can develop which are so high that they are found to cause radial yielding or fracture of the nut as a result of the forces acting upon the pipe and thereby the collet which is effectively united with the pipe. In this respect, it is to be appreciated that the pressure acts on the pipe in a direction tending to force it out of the sleeve. The result of this is that, because of the mutually engaging frusto-conical surfaces of the collet and the nut, extremely high radially-directed forces are exerted on the nut by the collet.

It is an object of the present invention to obviate or mitigate the above disadvantage.

According to the present invention, there is provided a pipe coupling comprising (a) a fastening member which is adapted to be secured to a co-operating part having a pipe-receiving bore therein, said fastening member being adapted to be passed over the pipe and having an internal frusto-conical surface region which flares outwardly in the direction of said co-operating part; and (b) an axially split collet which is engageable in the fastening member and over the pipe, said collet having an external frusto-conical surface which cooperates in use with the internal frusto-conical surface region of the fastening member, characterised in that substantially or generally radially directed abutment means are provided between the collet and the fastening member to limit axial movement of the collet relative to the fastening member in use in the direction of the frustum of the internal frustoconical region of the fastening member.

In a preferred embodiment, the abutment means is defined by an inwardly directed lip in the fastening mmember against which the frustum of the frusto-conical surface of the collet is engageable. In an alternative embodiment, the abutment means comprises an outwardly directed-flange at the base of the frusto-conical surface of the collet, said flange being engageable in a recess in the fastening member at the base of the internal frusto-conical surface region of the fastening member.

It is to be appreciated that the positioning of the abutment means on the collet and the fastening member will be chosen appropriately having regard to the angle of taper of the frusto-conical regions to ensure that mutual engagement of the abutment means will not interfere with correct engagement of the fastening member with the co-operating part and thereby gripping of the collet onto the pipe during assembly.

This invention is applicable to pipe couplings in which the fastening member is (a) a nut which may either be internally screw-threaded for engagement with an externally screw-threaded region on the co-operating part or externally screw-threaded for engagement with an internally screw-threaded region in the co-operating part, or (b) a member having a flange apertured to receive clamping bolts or the like which also pass through aligned apertures in a corresponding flange on the co-operating part.

The present invention will now be described in further detail with reference to the accompanying drawings, in which: Fig. 1 is a part cut-away perspective view of a pipe coupling of known type used to connect a pipe to a pipe connector body, and Fig.2 is an axial section through a nut which forms part of a pipe coupling according to an embodiment of the present invention.

Referring now to Fig. 1, the known pipe coupling comprises a nut 10 having an internally screw threaded end region 12, an internal, intermediate annular recess 14, and an internal frusto-conical region 16 extending from the recess 14 to the opposite end of the nut 10.

The frusto-conical region 16 flares outwardly towards the screw-threaded end region 12. The pipe coupling further comprises an axially split collet 18 which is disposed internally of the nut 10 and surrounds a pipe 20. The collet 18 has an external frusto-conical surface 22 which extends from one end of the collet 18 to the other. The collet 18 has an internal pipe-engaging surface 24 which is serrated to assist in gripping the external surface of the pipe 20.

The pipe coupling further comprises an O-ring seal 26 and a seal back-up washer 28. The above-described pipe coupling is shown connecting the pipe 20 to a pipe connector sleeve 30. Such sleeve 30 has a pair of externally screw threaded sleeves 32 and 34. The sleeve 32 has a stepped bore 36 in which the pipe 20 and the 0ring seal are engaged. The sleeve 34 is screwed into a body (not shown) to which the pipe is to be connected.

The back-up washer 28 is disposed partly within the stepped bore 36 and partly within intermediate recess 14 externally of the sleeve 32. It will be appreciated that tightening of the nut 10 on the sleeve 32 causes the collet 18, to be compressed radially inwardly so that it firmly grips the pipe 24 and is, in effect, unified therewith. Tightening of the nut 10 also serves to clamp the seal back-up washer 28 in position and thereby abut the O-ring seal 26 to ensure an adequate seal.

Hydraulic pressure within the pipe 20 acts on the pipe thus tending to urge it rearwardly, ie out of the sleeve 32. This force is applied to the collet 22 and is transmitted, by virtue of the frusto-conical surfaces 22 and 16, as a radially outward force on the nut 10. Under extreme pressure conditions, the forces generated can be such as to cause the nut 10 to yield or fracture radially. In this respect, it will be appreciated that the collet 22 can move rearwardly relative to the nut 10 and that the further it moves, the greater the radially outward force applied to the nut 10.

Referring now to Fig. 2, nut 110 illustrated therein is intended to replace the nut 10 described above and illustrated in Fig. 1. In nut 110, parts similar to those of nut 10 are accorded the same reference numerals but in the 100 series. Thus, nut 110 has internally screw-threaded end region 112, intermediate internal annular recess 114 and internal frusto-conical region 116. However, in this embodiment, frusto-conical region 116 does not extend completely to the opposite end of nut 110 remote from end region 112, but is limited in its axial extent by a substantially radially inwardly directed annular lip 140 providing one part of an abutment means whose other part is provided by the frustum 142 (see Fig. 1) of collet 18. The lip 140 is defined by a relatively thick annular rib 144 integral with the nut 110.

The combined axial dimension of the region 116 and the recess 114, together with the cone angle of the frustoconical surfaces and the diameter thereof are chosen having regard to the diameter of the pipe 20 so that the nut 110 can be properly tightened onto the sleeve 32 to hold the pipe 20 in position with the collet 22 gripping the latter and with the O-ring seal 26 properly compressed by the seal-back up washer 28 before the lip 140 engages the frustum 142 of the collet 18. It will be appreciated that, when extreme pressures are applied to the pipe coupling of Fig. 1 as modified by the provision of nut 110 of Fig. 2, the pipe 20 and collet 18 can only move a limited distance rearwardly until the frustum 142 of the collet 18 engages against the lip 140 to prevent further movement and thereby prevent any further increase in the radially outward force applied to the nut 110. In this manner, the risk of radial fracture or yielding of the nut 110 is mitigated.

Claims

1. A pipe coupling comprising (a) a fastening member which is adapted to be secured to a co-operating part having a pipe-receiving bore therein, said fastening member being adapted to be passed over the pipe and having an internal frusto-conical surface region which flares outwardly in the direction of said co-operating part; and (b) an axially split collet which is engageable in the fastening member and over the pipe, said collet having an external frusto-conical surface which cooperates in use with the internal frusto-conical surface region of the fastening member, characterised in that substantially or generally radially directed abutment means are provided between the collet and the fastening member to limit axial movement of the collet relative to the fastening member in use in the direction of the frustum of the internal frusto-conical region of the fastening member.

2. A pipe coupling as claimed in Claim 1, wherein the abutment means is defined by an inwardly directed lip in the fastening member against which the frustum of the frusto-conical surface of the collet is engageable.

3. A pipe coupling as claimed in Claim 1, wherein the abutment means comprises an outwardly directed flange at the base of the frusto-conical surface of the collet, said flange being engageable in a recess in the fastening member at the base of the internal frusto-conical surface region of the fastening member.

4. A pipe coupling as claimed in Claim 1, 2, or 3, wherein the fastening member is a nut which is internally screw-threaded for engagement with an externally screwthreaded region on the co-operating part.

5. A pipe coupling as claimed in any one of Claims 1 to 3, wherein the fastening member is a nut which is externally screw-threaded for engagement with an internally screw-threaded region in the co-operating part.

6. A pipe coupling as claimed in any one of Claims 1 to 3, wherein the fastening member is a member having a flange apertured to receive clamping bolts or the like which also pass through aligned apertures in a corresponding flange on the co-operating part.

7. A pipe coupling substantially as hereinbefore described with reference to Fig. 1 as modified by Fig. 2 of the accompanying drawings.