GB2043814A - Pipe Couplings - Google Patents

Abstract

A pipe coupling comprises a coupling body 1 having an externally screw-threaded sleeve 2 provided with a bore 3 into which an end of a pipe 4 is fitted. A sub-assembly of nut 5, collet 6, and back-up washer 7 is provided, the collet 6 being retained in the nut 5 by means of a retainer member 20 which has a turned up portion 22 forming a screw-threaded engagement with the threads in the nut 5. The washer 7 is retained in the nut 5 by a rib 17 and recess 16 thereof engaging with a recess 13 and rib 15, respectively, of the collet 6. The risk of damage to the threads of the nut 5 is reduced because the retainer member 20 is screw-engaged therewith rather than having to be forced past the screw threads and the collet 6 has a maximum diameter such that it is freely engageable in the nut 5. <IMAGE>

Description

SPECIFICATION Pipe Couplings This invention relates to pipe couplings and is particularly, though not exclusively, concerned with high pressure pipe couplings.

In high pressure pipe couplings, it is commonly the practice to provide a coupling comprising a coupling body including an externally screwthreaded sleeve into the bore of which an end of the pipe fits. The pipe coupling further includes an O-ring, a back-up washer, an anti-extrusion washer, a split collet and a securing nut. The Oring, back-up washer and anti-extrusion washer are engaged in the bore and are disposed around the end portion of the pipe. The nut engages with the external screw-threading on the sleeve of the body of the coupling and has an internal frustoconical surface which engages with a complementary frusto-conical surface on the collet so that, when the nut is tightened, the collet is urged against the end of the externally screwthreaded sleeve. This retains the O-ring, the backup washer and the anti-extrusion washer in position.The collet generally has an internal surface which is serrated so that when the nut is tightened the serrated internal surface of the collet bites into the surface of the pipe and so prevents the pipe from being forced out of the coupling under pressure in service. The antiextrusion washer prevents the O-ring from being extruded into the clearances inwardly and outwardly of the back-up washer by pressure within the pipe coupling in use.

The disadvantage of such a pipe coupling is that it consists of no less than five parts which have to be individually inserted on to the pipe before the end of the pipe is assembled into the coupling and these five parts have to be in the correct order and disposition for the coupling to operate correctly. With unskilled labour, it is quite easy to assembly the parts in the wrong order or disposition with the result that the seal will not be effective.

In order to overcome this problem, it has been proposed in British Patent Specification No.

1,233,372 to provide a sub-assembly of an axially split collar, an annular metal carrier or back-up member, and an annular seal. This sub-assembly is inserted as a unit into the nut. The carrier is held in engagement with the collar by way of an inwardly directed annular lip on the carrier which engages a portion of reduced diameter on the collar whilst an outwardly projecting annular lip on the collar adjacent the reduced diameter portion engages in an inwardly opening annular recess or rebate in the carrier.The carrier is engaged with the collar by deforming the latter inwardly as permitted by its axial split, then inserting the collar into the carrier until the lip on the carrier is aligned with the reduced diameter portion and the lip on the collar is aligned with the annular recess in the carrier, and then releasing the collar so that it expands radially to secure itself to the carrier. A similar arrangement is provided between the annular seal and the carrier with the seal being radially inwardly contracted to connect it with the carrier. In this sub-assembly, the seal is supported by the carrier which, in turn, is supported by the collar. This construction relies on an interference fit between the collar and the threading in the nut to retain the sub-assembly in position and so the collar has to be radially contracted to fit into the nut.During this fitting operation, there is a strong risk of the collar scoring the threading and of plating on the interference fit parts being damaged.

Additionally, there is a risk that radial contraction of the collar during fitting into the nut will cause the carrier to be at least partially disengaged from the collar.

It has also been proposed in British Patent Specification No. 1,522,203 to provide a construction in which a serrated collet is retained in a nut by means of a rubber ring which is bonded to the outer periphery of a back-up washer. The rubber ring has an uncompressed external diameter which is greater than the free diameter of the screw-threading in the nut. During assembly, the collet is inserted into the nut and retained in position by the back-up washer which is inserted as a separate item into the nut and has to be forced along the screw-threads because of the provision of the rubber ring thereon. The engagement of the rubber ring with the nut holds the back-up washer and collet in position.This type of arrangement has the disadvantage that a very positive attachment is not provided between the collet and the nut so that when the coupling is dismantled by unscrewing the nut, there is a risk that the collet and backup washer will not be withdrawn with the nut to enable easy access to the O-ring for servicing. It is to be appreciated that a positive attachment is required because the serrations on the collet tend to grip the surface of the pipe making the collet difficult to remove.

Furthermore, with the construction of British Patent Specification No. 1,522,203, it is possible to insert the back-up washer into the nut the wrong way round and there is even a risk that the collet will be completely omitted. Further, the use of a rubber ring is not preferred as it can become damaged due to abrasion against the screwthreading during insertion into the nut with the result that it may not act properly to retain the parts within the nut and a sealed joint may not be obtained if some of the material from the damaged rubber ring becomes lodged against one of the sealing surfaces in the coupling.

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

According to the present invention, there is provided a pipe coupling comprising a coupling body having an externally screw-threaded sleeve provided with a bore into which an end of a pipe is fitted, in use, and a sub-assembly of nut, collet and back-up washer, wherein means act between the collet and the nut for retaining the collet in the nut, means secure the back-up washer to the collet, the collet has a maximum diameter which is not greater than the free diameter of screwthreading in the nut, and the means is engaged in screw-threaded manner with the nut.

In one embodiment, the collet retaining means engages in a rebated portion at the base of screw threading in the nut so as to prevent relative movement between the collet and the nut in one axial direction, relative movement between the collet and the nut in the opposite axial direction being prevented by mutually engaging surfaces on the nut and the collet.

The back-up washer may be a snap-fit engagement with the collet and may be formed of a plastics material, e.g. nylon. Alternatively, the back-up washer may be formed of metal.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings in which:~ Fig. 1 is an axial section through one embodiment of pipe coupling according to the present invention, Fig. 2 is an axial section through parts of a second embodiment of pipe coupling according to the present invention, and Fig. 3 is a perspective view of a retainer member used in the pipe coupling of Fig. 1 or Fig.

2.

Referring now to Fig. 1 of the drawing, the pipe coupling illustrated therein comprises a coupling body 1 including an externally screw-threaded sleeve 2 having an internal bore 3 into which an end portion of a pipe 4 is fitted. The coupling also comprises a sub-assembly of a nut 5, a collet 6, a sleeve or back-up washer 7 which also acts as an anti-extrusion washer, and a separate O-ring 9.

The nut 5 is of a size to engage with the screwthreading externally of the sleeve 2 and is provided internally with a frusto-conical surface 10 which tapers inwardly away from the screwthreading. The collet 6 is formed of metal and is split axially (not shown). The collet 6 has a frustoconical external surface 11 which corresponds to the frusto-conical surface 10 and has a maximum external diameter (in a radially uncompressed state) which is less than the free diameter of the screw-threading in the nut 5, i.e. less than the diameter of the peaks of the screw-threading in the nut 5. Thus, the collet 6 is freely engageable even in a radially uncompressed state in the nut 5.

The collet 6 is also provided at one end thereof with a serrated internal surface 12. At its end opposite to that at which the surface 12 is provided, the collet 6 has an internal annular recess 13 defined by an abutment surface 14 and an internal annular rib 15. The abutment surface 14 extends radially outwardly with respect to the axis of the collet 6. The back-up washer 7 is in the form of a continuous annular sleeve formed of nylon. The external peripheral surface of the backup washer 7 is provided with a recess 16 therein which is complementary in shape to that of the rib 15. and is also provided with a rib 17.The backup washer 7 is engaged, in a snap-fit manner, with the collet 6 to be carried thereby with the rib 15 engaging in the recess 16 and the rib 17 engaging in the recess 13 with one axial end of the back-up washer 7 abutting against the abutment surface 14. This snap-fit engagement is permitted because the axial split in the collet 6 allows the latter to be expanded outwardly in a resilient manner. The opposite axial end 18 of the back-up washer is concave and curved to conform to that of the O-ring 9. The washer 7 serves both as a back-up and as an anti-extrusion washer for the O-ring 9. In a modification (not shown) the washer 7 has an annular end portion which is joined to the remainder of the washer 7 by an integral annular neck portion. This annular end portion has a concave end surface like the end 18 described above.

The collet 6 and thus the washer 7 are retained in the nut by a retainer member 20 which is shown in greater detail in Fig. 3. The retainer member 20 takes the form of an annular metal washer having an internal diameter which is marginally greater than the external diameter of the back-up washer 7. The member 20 has an external diameter which is greater than the maximum diameter of the collet and the aforementioned free diameter of the screwthreading in the nut 5 but which is less than the valley-to-valley diameter of the screw-threading.

The member 20 has a thickness such that it can fit between adjacent peaks of the screw-threading in the nut 5. Additionally, the member 20 has a rectangular recess 21 cut into its outer periphery.

A portion 22 of the member 20 on the right-hand side of the recess 21 (as viewed in Fig. 3) is turned up out of the general plane of the member 20 to provide an abutment edge 23 which lies out of the general plane of the member 20. As can be seen from Fig. 1 , the member 20 engages in a rebated portion 24 in the nut 5 at the base of the screw-threading therein and also abuts against that end face of the collet 6 which is adjacent the rib 1 5. The member 20 with its portion 22 defines, in effect, a single turn of a helix and so can be engaged, in screw-threaded manner with the screw-threading in the nut 5.As mentioned above, the nut 5 and the collet 6 and the back-up washer 7 are provided as a sub-assembly retained together by the member 20 so that, in effect, there are only three separate parts to the pipe coupling, namely the sub-assembly, the coupling body 1 and the O-ring 9.

During formation of the sub-assembly, first the back-up washer 7 is snap-fitted into engagement with the collet 6 in the manner described above.

Then the retainer member 20 is passed over the back-up washer 7 until it engages against the collet 6 with the portion 22 extending on the opposite side of the general plane of the member 20 to the collet 6. The collet 6 is then inserted into the nut 5 until the retainer member engages against the entrance to the screw-threading in the nut 5. A special tool (not shown) in the form of a tube having a single small driving projection is engaged with the retainer member 20 around the back-up washer 7 with the driving projection extending into the recess 21 in the member 20.

Turning of the tool causes the retainer member 20 to rotate and travel along the screw threading in the nut 5 until it reaches the rebated portion 24. Thus, the retainer member 20 holds the collet 6 in the nut 5 and the collet 6 retains the back-up washer 7 in the nut 5 to form the aforementioned sub-assembly. Because the collet 6 does not need to be radially compressed to engage in the nut and because the retainer member 20 is not forced axially over the threading in the nut 5 but screwengaged therewith, there is little chance of damage being caused to parts of the subassembly during assembly thereof and there is little risk therefore of material being removed by abrasion and contaminating the sealing surface of the completed coupling. Additionally, the collet 6 is very positively held in position in the nut 5 and so can be readily withdrawn as a unit for servicing of the O-ring 9.

In order to assemble the pipe coupling, it is merely necessary for a fitter to insert the end of the pipe 4 into the pipe coupling 1 after first having engaged O-ring 9 and the aforementioned sub-assembly over the end of the pipe 4. The fitter then merely screws the nut 5 on to the sleeve 2 to complete the coupling. As will be readily apparent, the O-ring 9 is deformed to seal around the periphery of the end portion of the pipe 4 and the internal surface of the bore 3 in the sleeve 2. The pipe 4 is prevented from being forced out of the bore 3 because the serrated surface 12 bites into the surface of the pipe 4 when the nut 5 is tightened due to the wedging action obtained between the two frusto-conical surfaces 10 and 11 and the ability of the collet 6 to compress inwardly because it is split.

In the above-described pipe coupling, it will be apparent that there is a minimum possibility of the parts being assembled in the wrong order because of the provision of the nut 5, collet 6 and the back-up washer 7 as a sub-assembly with one separate component, namely the O-ring 9.

Referring now to Fig. 2, a back-up washer 27 formed of metal is provided in place of the nylon back-up washer 7. In this embodiment, the backup washer 27 does not itself serve an antiextrusion function but has a separate nylon antiextrusion washer 28 adhesively secured thereto by, for example, a composition sold under the trade mark Loctite. The metal back-up washer 27 and the nylon anti-extrusion washer 28 can be used in pipe coupling systems where a nylon back-up washer is not suitable. In order to assemble the back-up washer 27 with the collet 6, it is necessary to open up the collet 6, as permitted by the split therein in order to engage the ribs with the respective recesses. In an alternative embodiment (not shown) the washers 27 and 28, instead of being adhesively secured together, are secured together by a rib and recess arrangement similar to the arrangement used to secure the collet 6 and back-up washer 27 together.

It will be appreciated that it may be necessary to provide a variety of different types of O-ring 9 to suit the particular pressure temperature and fluid characteristics for which the pipe coupling is intended.

Claims (8)

Claims

1. A pipe coupling comprising a coupling body having an externally screw-threaded sleeve provided with a bore into which an end of a pipe is fitted, in use, and a sub-assembly of nut, collet and back-up washer wherein means act between the collet and the nut for retaining the collet in the nut, means secure the back-up washer to the collet, the collet has a maximum diameter which is not greater than the free diameter of the screwthreading in the nut, and the collet retaining means is engaged in screw-threaded manner with the nut.

2. A pipe coupling as claimed in claim 1, wherein the collet retaining means engages in a rebated portion at the base of screw threading in the nut so as to prevent relative movement between the collet and the nut in one axial direction, and relative movement between the collet and the nut in the opposite axial direction is prevented by mutually engaging surfaces on the nut and the collet.

3. A pipe coupling as claimed in claim 2, wherein said mutually engaging surfaces are tapered surfaces.

4. A pipe coupling as claimed in claim 1, 2 or 3, wherein the means for securing the back-up washer to the collet comprises complementary formations on the back-up washer and the collet which are interengaged to secure the back-up washer to the collet.

5. A pipe coupling as claimed in claim 4, wherein the complementary formations are engaged with a snap-fit connection.

6. A pipe coupling as claimed in any preceding claim, wherein the collet retaining means comprises a member having a single turn helix.

7. A pipe coupling as claimed in claim 6, wherein said member comprises an annular washer having a slot in its outer periphery with a portion of the washer on one side of the slot being bent out of the general plane of the washer.

8. A pipe coupling substantially as hereinbefore described with reference to Figs. 1 and 3 or Figs.

1 and 3 as modified by Fig. 2 of the accompanying drawing.