GB1602356A

GB1602356A - Pipe coupling

Info

Publication number: GB1602356A
Application number: GB2077978A
Authority: GB
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1978-05-19
Filing date: 1978-05-19
Publication date: 1981-11-11

Description

(54) PIPE COUPLING (71) We, LUCAS INDUSTRIES LIMITED, a British company, of Great King Street, Birmingham B 19 2XF, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a pipe coupling and is more particularly concerned with a pipe coupling of the type comprising a body having an externally screw-threaded sleeve with a bore therein which receives, in use, an end of a pipe to be coupled with the body, a wall of the bore including a stepped region, a back-up member extending into the bore to define with the stepped region an annular recess surrounding the pipe in use, a nut engaging the sleeve in use and serving to retain the back-up member in position, and a deformable sealing ring disposed in said annular recess, the arrangement being such that tightening of the nut causes the sealing ring to effect a seal between the tube and the body.

It is known to provide a pipe coupling of the above described type in which the deformable sealing ring takes the form of a rubber O-ring of circular cross-section. This rubber O-ring is generally satisfactory under normal conditions although it can fail if the pipe coupling is used in systems containing fluids which are corrosive to the rubber 0ring. Additionally, under high temperature conditions, e.g. when a fire occurs in the region of the pipe coupling, melting of the sealing ring can result in leakage. Furthermore, rubber O-rings are relatively easily damaged upon assembly of the pipe coupling with the result that their sealing properties can be deleteriously affected. In the past, it has not bee practical to use a loosely preassembled coupling with an O-ring seal in position because of damage to the O-ring.

It is therefore an object of a preferred embodiment of the present invention to obviate or mitigate the above disadvantages.

A rubber O-ring also suffers from the disadvantage that it is prone to break-up in installation where the pipe is subjected to severe vibrations which cause local axial movement of the pipe in the region of the 0ring. It is believed that this is caused by the relatively large area of contact between the pipe and the O-ring.

It is therefore 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 body having an externally screw-threaded sleeve with a bore therein which receives, in use, an end of a pipe to be coupled with the body, a wall of the bore including a stepped region, a back-up member extending into the bore to define with the stepped region an annular recess surrounding the pipe in use, a nut engaging the sleeve in use and serving to retain the back-up member in position, a collet in the nut for gripping the pipe and a deformable sealing ring disposed in said annular recess, said sealing ring being of frusto-conical form with the top of the frustum abutting against the back-up member and the base of the frustum sealingly engaging against the step in the wall of the bore or vice versa so that, in use, an inner periphery of the sealing ring adjacent the top of the frustum is sealingly engaged around the pipe and an outer periphery of the sealing ring adjacent the base of the frustum is sealing engaged with the wall of the bore, the inner periphery of the sealing ring being cylindrical.

Preferably, the sealing ring is metal. The use of a metal sealing ring gives temperature resistance and enables the loose pre-assembly of the coupling.

Preferably said outer periphery of the sealing ring is cylindrical.

In a preferred embodiment, the top of the frustum is defined by an annular surface which extends perpendicularly with respect to the axis of the ring.

The included angle of the frustum is preferably 5(}75 .

The sealing ring is preferably formed of copper or copper alloy although any other malleable metal may be employed.

An embodiment 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, on a larger scale, of a sealing ring illustrated in Fig. 1, and Fig. 3 is an axial section through part of a second embodiment of a pipe coupling according to the present invention.

Referring now to Fig. 1, the pipe coupling comprises a hollow connector body 10 having a pair of integral, oppositely directed, externally screw-threaded sleeves 11 and 12.

A bore 13 extends completely through the body 10 and has two steps 14 and 15 therein within the sleeve 11. The bore 13 is of circular cross-section and is outwardly flared at its ends. The pipe coupling further includes a nut 16 engageable with the sleeve 11 and having an internal frusto-conical surface 17 which tapers inwardly away from the sleeve 11. The frusto-conical surface 17 is axially displaced from screw-threading 18 on the nut 16. Disposed within the nut 16 is a collet 19 which is axially split (in the section shown in Fig. 1 the axial split in the collet is not shown). The collet 19 has a frusto-conical external surface 20 which engages with the frusto-conical surface 17 in the nut 16. The internal surface 21 of the collet 19 is generally cylindrical and is serrated. The pipe coupling additionally includes a back-up washer 22. The back-up washer 22 comprises an axially directed sleeve portion 23 and a radially directed annular flange portion 24.

The outer diameter of the sleeve portion 23 is marginally less than the inside diameter of the portion of the bore 13 which is intended to receive the sleeve portion 23. The portion of the bore 13 in the region of the step 14 defines, with the axial end of the sleeve portion 23 remote from the flange portion 24, an annular recess 25 which is of rectangular shaped cross-section.

Disposed within the recess 25 is a frustoconical metal sealing ring 26 which, in this embodiment, is formed of a copper alloy having a Vickers hardness of 75 (1/4 hard copper alloy).

Referring now to Fig. 2, the frusto-conical sealing ring 26 has an annular base 27 which extends in a plane perpendicular to the longitudinal axis of the sealing ring 26. The top 28 of the sealing ring 26 is also defined by an annular surface extending in a plane perpendicular to the longitudinal axis of the ring 26. Adjacent the top 28 of the sealing ring 26, there is provided an inner peripheral surface 29 which is of cylindrical form with the axis of the cylinder lying on the longitudinal axis of the ring. Similarly, the outer periphery of the ring 26 in the region of the base 27 is defined by a cylindrical surface 30 whose longitudinal axis lies on the longitudinal axis of the sealing ring 26.

In Fig. 2, the angle A represents the included angle of the frusto-conical surface of the sealing ring 26. The dimension B represents the maximum external diameter of the ring 26 and corresponds to the diameter of the cylindrical surface 30. The dimension C represents the total length of the ring 26 in the axial direction and corresponds to the distance between the surfaces 27 and 28. The dimension D represents the minimum internal diameter of the ring 26 and corresponds to the diameter of the cylindrical surface 29. Dimension E represents the length of the cylindrical surface 30 and the length of the cylindrical surface 29 has the same dimension. The dimension T represents the thickness of the ring.

In the above embodiment which is for a 10 mm diameter pipe, the dimensions are as follows: A = 54 B = 0.563 - .003 in.

C = 0.144 - .005 in.

D = 0.399 + .002 in.

E = 0.030 + .005 in.

T = 0.030 + .005 in.

During assembly of the pipe coupling, the nut 16 and the collet 19 are passed over the end of a pipe 31. The sealing ring 26 is inserted into the bore 13 so that its base 27 abuts against the step 14. Following this, the back-up washer 22 is engaged with the sleeve 11 so that the end of the sleeve portion 23 thereof abuts against the top 28 of the sealing ring 26. In this position, the flange portion 24 is spaced from the free end of the sleeve 11.

Then the end portion of the pipe 31 is inserted into the sleeve 11 until the end of the pipe 31 abuts against the step 15. It will be appreciated that the diameter of the bore 13 between the steps 14 and 15 is slightly greater than the outer diameter of the pipe 31. The screw-threading 18 on the nut 16 is then engaged with the external screw-threading on the sleeve 11 and the nut 16 is rotated.

Rotation of the nut 16 causes the collet 19 to move axially towards the sleeve 11 and so urges the back-up washer 22 further towards the sleeve 11. The nut 16 is then tightened to a predetermined torque in the range of 15-500 ft.lb so that the annular flange portion 24 does not engage against the free end of the sleeve 11 but is spaced therefrom by a distance of 0.75 mm to 1.5 mm depending upon the diameter of the pipe.

Tightening of the nut 16 causes the frustoconical surface 20 to deform the collet 19 radially inwardly as permitted by the axial slit. This causes the serrated internal surface 21 of the collet 19 to bit into the external surface of the pipe 31 to hold same against unwanted axial movement in a direction out of the sleeve 11. The axial movement of the sleeve portion 23 of the back-up washer 22 during the tightening of the nut 16 causes the sealing ring 26 to be compressed in the axial direction. Axial compression of the ring 26 is accompanied by outward expansion of the base 27 and inward compression of the top 28 so that the surface 29 seals against the outer periphery of the tube 31 and the surface 30 seals against the wall of the bore 13 which defines part of the annular recess 25. Sealing also occurs as a result of engagement of the base 27 against the step 14 and engagement of the top 28 against the end of the sleeve portion 23 remote from the annular flange portion 24.

The above-described pipe coupling is found to be pressure-resistant to extremely high pressures of up to 10,000 p.s.i. and is extremely resistant to high temperatures in view of the material chosen for the sealing ring 26.

In an alternative embodiment, the sealing ring 26 is fitted in the annular recess between the step 14 and the sleeve portion 23 in the manner shown in Fig. 3, so that the top 28 thereof engages against the step 14 and the base 27 engages against the end of sleeve portion 23 remote from the annular flange portion 24. The arrangement shown in Fig. 1 is, however, preferred.

The pipe couplings described above are suitable for fluids to which the copper alloy of the sealing ring is inert but which would, nevertheless, corrode a conventional rubber O-ring seal.

The above-described pipe couplings can be taken apart and re-assembled at least four times using the same sealing ring.

Although a copper alloy sealing ring has been described in the above embodiments, it is possible to use any other deformable metal sealing ring, for example MONEL (Registered Trade Mark) metal or mild or stainless steel, or, for lower temperature-resistant purposes, aluminium. For even lower temperature applications and lower pressure applications, it is possible to use a sealing ring formed of a thermoplastics material, e.g. a polyethylene, polypropylene, polystyrene, acetal resin (e.g. DELRIN Registered Trade Mark), nylon (with or without glass filling), P.T.F.E., or A.B.S. resin. A metal or a plastics sealing ring can be used in conjunction with a pipe coupling formed of metal. In the case of a pipe coupling formed of plastics, a plastics sealing ring will normally be used.

The dimensions A, B, C, D, E and T may vary depending upon the diameter of the pipe.

Another advantage of the above-described construction is that there is less chance of the metal sealing ring 26 failing to make an effective seal in the case where pressure pulses occur in a pipe coupling in service.

Pressure pulses in conventional pipe couplings using rubber O-rings can cause extrusion of the rubber and subsequent leakage.

This is a known problem and it is known to provide an anti-extrusion washer between the O-ring and the back-up member in order to prevent such extrusion. The use of an antiextrusion washer is avoided using the abovedescribed sealing ring.

WHAT WE CLAIM IS: 1. A pipe coupling comprising a body having an externally screw-threaded sleeve with a bore therein which receives, in use, an end of a pipe to be coupled with the body, a wall of the bore including a stepped region, a back-up member extending into the bore to define with the stepped region an annular recess surrounding the pipe in use, a nut engaging the sleeve in use and serving to retain the back-up member in position, a collet in the nut for gripping the pipe, and a deformable sealing ring disposed in said annular recess, said sealing ring being of frusto-conical form with the top of the frustum abutting against the back-up member and the bottom of the frustum sealingly engaging against the step in the wall of the bore or vice versa so that, in use, an inner periphery of the sealing ring adjacent the top of the frustum is sealingly engaged around the pipe and an outer periphery of the sealing ring adjacent the base of the frustum is sealingly engaged with the wall of the bore, the inner periphery of the sealing ring being cylindrical.

2. A pipe coupling as claimed in claim 1, wherein the sealing ring is of metal.

3. A pipe coupling as claimed in claim 2, wherein the sealing ring is of copper or copper alloy.

4. A pipe coupling as claimed in claim 2 or 3, wherein the metal has a Vickers hardness of 75.

5. A pipe coupling as claimed in claim 1, wherein the sealing ring is of plastics.

6. A pipe coupling as claimed in any preceding claim, wherein said outer periphery of the sealing ring is cylindrical.

7. A pipe coupling as claimed in any preceding claim, wherein the top of the frustum is defined by an annular surface extending perpendicular to the axis of the ring.

8. A pipe coupling as claimed in any preceding claim, wherein the base of the frustum is defined by an annular surface extending perpendicular to the axis of the ring.

9. A pipe coupling as claimed in any preceding claim, wherein the included angle of the frustum of the sealing ring is 50"--75".

10. A pipe coupling substantially as hereinbefore described with reference to

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. unwanted axial movement in a direction out of the sleeve 11. The axial movement of the sleeve portion 23 of the back-up washer 22 during the tightening of the nut 16 causes the sealing ring 26 to be compressed in the axial direction. Axial compression of the ring 26 is accompanied by outward expansion of the base 27 and inward compression of the top 28 so that the surface 29 seals against the outer periphery of the tube 31 and the surface 30 seals against the wall of the bore 13 which defines part of the annular recess 25. Sealing also occurs as a result of engagement of the base 27 against the step 14 and engagement of the top 28 against the end of the sleeve portion 23 remote from the annular flange portion 24. The above-described pipe coupling is found to be pressure-resistant to extremely high pressures of up to 10,000 p.s.i. and is extremely resistant to high temperatures in view of the material chosen for the sealing ring 26. In an alternative embodiment, the sealing ring 26 is fitted in the annular recess between the step 14 and the sleeve portion 23 in the manner shown in Fig. 3, so that the top 28 thereof engages against the step 14 and the base 27 engages against the end of sleeve portion 23 remote from the annular flange portion 24. The arrangement shown in Fig. 1 is, however, preferred. The pipe couplings described above are suitable for fluids to which the copper alloy of the sealing ring is inert but which would, nevertheless, corrode a conventional rubber O-ring seal. The above-described pipe couplings can be taken apart and re-assembled at least four times using the same sealing ring. Although a copper alloy sealing ring has been described in the above embodiments, it is possible to use any other deformable metal sealing ring, for example MONEL (Registered Trade Mark) metal or mild or stainless steel, or, for lower temperature-resistant purposes, aluminium. For even lower temperature applications and lower pressure applications, it is possible to use a sealing ring formed of a thermoplastics material, e.g. a polyethylene, polypropylene, polystyrene, acetal resin (e.g. DELRIN Registered Trade Mark), nylon (with or without glass filling), P.T.F.E., or A.B.S. resin. A metal or a plastics sealing ring can be used in conjunction with a pipe coupling formed of metal. In the case of a pipe coupling formed of plastics, a plastics sealing ring will normally be used. The dimensions A, B, C, D, E and T may vary depending upon the diameter of the pipe. Another advantage of the above-described construction is that there is less chance of the metal sealing ring 26 failing to make an effective seal in the case where pressure pulses occur in a pipe coupling in service. Pressure pulses in conventional pipe couplings using rubber O-rings can cause extrusion of the rubber and subsequent leakage. This is a known problem and it is known to provide an anti-extrusion washer between the O-ring and the back-up member in order to prevent such extrusion. The use of an antiextrusion washer is avoided using the abovedescribed sealing ring. WHAT WE CLAIM IS:

1. A pipe coupling comprising a body having an externally screw-threaded sleeve with a bore therein which receives, in use, an end of a pipe to be coupled with the body, a wall of the bore including a stepped region, a back-up member extending into the bore to define with the stepped region an annular recess surrounding the pipe in use, a nut engaging the sleeve in use and serving to retain the back-up member in position, a collet in the nut for gripping the pipe, and a deformable sealing ring disposed in said annular recess, said sealing ring being of frusto-conical form with the top of the frustum abutting against the back-up member and the bottom of the frustum sealingly engaging against the step in the wall of the bore or vice versa so that, in use, an inner periphery of the sealing ring adjacent the top of the frustum is sealingly engaged around the pipe and an outer periphery of the sealing ring adjacent the base of the frustum is sealingly engaged with the wall of the bore, the inner periphery of the sealing ring being cylindrical.

2. A pipe coupling as claimed in claim 1, wherein the sealing ring is of metal.

10. A pipe coupling substantially as hereinbefore described with reference to

figs. I and 2 or Fig. 3 of the accompanying drawing.

11. An assembly of a pipe and a pipe coupling as claimed in any preceding claim, wherein the back-up member has a flange which is capable of limiting compression of the seal by abutment with the sleeve, but wherein the nut is tightened only to an extent that the flange is spaced from the sleeve.