GB2389881A

GB2389881A - A coupling

Info

Publication number: GB2389881A
Application number: GB0214323A
Authority: GB
Inventors: Barry Wilder
Original assignee: SEV GLOCON Ltd
Current assignee: SEV GLOCON Ltd
Priority date: 2002-06-21
Filing date: 2002-06-21
Publication date: 2003-12-24
Also published as: GB0214323D0

Abstract

A coupling comprising a first coupling member (10) formed from a first material and having a first seating portion (20), a second coupling member (12) formed from a second material and having a second seating portion (16), means coupling the first and second coupling members together, and a seal element (24) interposed between the first and second coupling members and seated on the first and second seating portions, the seal element being formed of a third material which, when the coupling is to be subjected to temperatures below ambient, has a higher coefficient of expansion than at least one of the said first and second materials and which, when the coupling is to be subjected to temperatures above ambient, has a lower coefficient of expansion than at least one of the said first and second materials.

Description

1 2389881

A COUPLING

This invention relates to a coupling and more particularly, but not exclusively, to a coupling which forms part of a valve, such as a cryogenic valve.

It is common practice in cryogenic valves to seal a valve seat to a valve body with a seal of a material which seals at room temperature. Such seals suffer from the drawback that they lose their sealing efficiency as the temperature drops. It is also conventional to connect the valve seat to the valve body with a threaded connection.

10 When the seal leaks the connection is also capable of unscrewing and this makes the leak worse.

The present invention seeks to provide an improved seal between two coupling members such as, for example, a valve seat and valve body of a cryogenic valve.

According to the present invention, there is provided a coupling comprising a first coupling member formed from a first material and having a first seating portion, a second coupling member formed from a second material and having a second seating portion, means coupling the first and second coupling members together, and 20 a seal element interposed between the first and second coupling members and seated on the first and second seating portions, the seal element being formed of a third material which, when the coupling is to be subjected to temperatures below ambient,

l ( has a higher coefficient of expansion than at least one of the said first and second materials and which, when the coupling is to be subjected to temperatures above ambient, has a lower coefficient of expansion than at least one of the said first and second materials.

Preferred and/or optional features of the invention are set forth in claims 2 to 19. The invention will now be more particularly described, by way of example, 10 with reference to the accompanying drawings, in which: Figure I is a partial cross-section of a cryogenic valve having a first embodiment of a coupling between a valve seat and a valve body according to the invention, Figure 2 is an enlarged fragmentary sectional view of the coupling shown in Figure 1, Figure 3 is an enlarged fragmentary sectional view of a second embodiment of 20 a coupling between a valve seat and a valve body of a cryogenic valve according to the invention, and

( Figure 4 is an enlarged fragmentary sectional view of a third embodiment of a coupling between a valve seat and a valve body of a cryogenic valve according to the invention. 5 Referring to Figures 1 and 2 of the drawings, the coupling shown therein comprises a valve seat 10 and a valve body 12. The valve seat 10 and the valve body 12 form part of a cryogenic valve of a type such as is, by way of example, described in GB-A-2335022. Cryogenic valves typically operate at temperatures of - 198 C or lower, although these valves will from time to time be operated under pressure at 10 ambient temperatures.

The valve body 12 has a through bore 14 of stepped diameter. The upper portion 1 4a of the through bore is of larger diameter than the lower portion 14_ of the through bore. The lower portion 14b is internally threaded. An annular radially 1 S extending seating portion 16 is defined between the upper and lower portions 14a and 14b. The valve seat 10 is of annular shape and has a stepped external diameter having an upper portion 18a of larger diameter than the lower portion 1 8b. The 20 upper portion 1 8a is a slidable fit within the upper portion 14a of the through bore of the valve body 12 and the lower portion 1 8b is externally threaded so as to co-operate with the internal thread on the lower portion 14b of the through bore in the valve

( body 12.

An annular seating portion 20 is formed between the upper portion 1 8a and the lower portion lab. This seating portion 20 is chamfered or upwardly inclined in a 5 radially outwards direction. The valve seat 10 also has an internal seating portion 22 for making sealing contact with an openable and closable valve plug 23.

The valve seat 10 and valve body 12 are typically made of stainless steel, low-

temperature carbon steel, bronze or Monel. The valve seat 10 and valve body 12 10 may, however, be formed of different materials from one another.

An annular seal 24 is interposed between the seating portion 16 on the valve body 12 and the seating portion 20 on the valve seat 10. The seal 24 is formed of non-elastomeric material and preferably a metal, typically soft aluminium, which has 15 a higher coefficient of expansion than at least the material of the valve seat 10.

Preferably, the material of the seal 24 has a higher coefficient of expansion than both the material of the valve seat 10 and the material of the valve body 12.

The seal 24 has a chamfered or upwardly radially outwardly inclined upper 20 surface 24a so as to be complementary with the chamfered seating portion 20 of the seat 10 and a lower radially outwardly extending surface 24b for contact with the seating portion 20 of the valve body 12. The seal 24 preferably has a low-friction

i outer layer, which is preferably in the form of a metallic coating and typically in the form of a layer of Indium. It could, however, have other low-friction outer layers such as PTFE or it could be lubricated with oil.

5 The threaded joint between the valve seat 10 and valve body 12 is tightened sufficiently at ambient temperatures to cause some plastic deformation of the material of the component parts. When the valve is used at cryogenic temperatures, the material of the seal 24, which has a higher coefficient of expansion than at least the material of the valve seat 10, shrinks as it gets colder faster than the material of the 10 seat 10. This increases the wedging action between the seal 10 and the body 12, thus keeping the joint pressure tight and the seat 10 sufficiently stressed to prevent unscrewing. Only the radially inner portion of the upper surface of the seal 24 need be 1 5 chamfered.

Obviously, if the lower surface 24b of the seal 24 is chamfered instead of the upper surface 24_, and the seating portion 16 of the valve body 12 is chamfered instead of the seating portion 20, then the material of the seal 24 needs to have a 20 higher coefficient of expansion than at least the material of the valve body 12.

As shown in Figure 3, in a second embodiment of the coupling, at least the

( radially inner portions of both the upper and lower surfaces 24a' and 24b' of the seal 24' could be chamfered so as to co-operate with complementary chamfers on the seating portions 20' and 16' of the valve seat 10' and the valve body 12'. This can further enhance the wedging action, but is more expensive to machine.

s For higher than ambient temperature applications, the seal 24/24' is formed of a material having a lower coefficient of expansion than the material of at least the valve seat 10/10' so that, as the temperature increases, it expands more slowly than the seat 10/10'.

Figure 4 shows a third embodiment in which a clamp 28 is used to clamp the seal 24" between the valve seat 10" and the valve body 12'', instead of the screw threads of the embodiment shown in Figure 1.

15 As with the second embodiment, opposing chamfers could be formed to further enhance the wedging action.

The valve body seating portion and/or the valve seat seating portion need not necessarily be chamfered if there is an outer edge, for example in Figure 2 the edge 20 30 between the outer surface 14_ of the valve seat 10 and the seating portion 20, on which the seal can wedge. In this case, the wedge seal has an initial outer diameter which is larger than the diameter of the upper portion 1 8a of the valve seat 10. The

coupling is assembled so that the maximum distance between the opposing seating portions is less than the maximum thickness of the wedge seal. Consequently, as the temperature changes, the chamfered upper surface of the wedge seal becomes wedgingly engaged with the edge 30.

s The seating portions of the valve body and valve seat could thus be parallel to each other and not chamfered.

It may also be possible, if the wedge seal is formed from a malleable material 10 such as aluminium, that the seal could be initially formed without a chamfer, i.e. flat.

Providing the valve seat seating portion and/or the valve body seating portion is-

chamfered, a corresponding chamfer will be formed on the seal when the coupling is in use.

15 The above embodiments are given by way of example only and various modifications will be apparent to persons skilled in the art without departing from the scope of the invention as defined in the appended claims. For example, this arrangement could be used with any coupling that undergoes suitable variations in temperature when in use.

Claims

( CLAIMS

A coupling comprising a first coupling member formed from a first material and having a first seating portion, a second coupling member formed from a second 5 material and having a second seating portion, means coupling the first and second coupling members together, and a seal element interposed between the first and second coupling members and seated on the first and second seating portions, the seal element being formed of a third material which, when the coupling is to be subjected to temperatures below ambient, has a higher coefficient of expansion than at least one 10 of the said first and second materials and which, when the coupling is to be subjected to temperatures above ambient, has a lower coefficient of expansion than at least one of the said first and second materials.
2. A coupling as claimed in claim 1, wherein, when the coupling is to be 15 subjected to temperatures below ambient, the third material of the seal element has a higher coefficient of expansion than both the said first and second materials and, when the coupling is to be subjected to temperatures above ambient, the material of the seal element has a lower coefficient of expansion than both of the said first and second materials.
3. A coupling as claimed in claim I or claim 2, wherein the first and second materials of the first and second coupling members are the same material.
4. A coupling as claimed in claim I or claim 2, wherein the first and second materials of the first and second coupling members are different materials.
5. A coupling as claimed in any one of the preceding claims, wherein the third 5 material of the seal element is metal.
6. A coupling as claimed in any one of the preceding claims, wherein the top surface or the bottom surface of the seal element and the first seating portion or the second seating portion are formed with complementary chamfers to, in use, promote 10 wedging engagement between the seal element and the first and second coupling members.
7. A coupling as claimed in any one of claims I to 5, wherein the top and bottom surfaces of the seal element and the first and second seating portions of the coupling 15 members are formed with complementary chamfers to, in use, promote wedging engagement between the seal element and the first and second coupling members.
8. A coupling as claimed in claim 6 or claim 7, wherein the chamfer(s) of the seal element inwardly taper.
9. A coupling as claimed in any one of the preceding claims, wherein, in use, the seal element fluid-tightly seals the coupling.

(
10. A coupling as claimed in any one of the preceding claims, wherein the seal element includes a low-friction outer layer.
A coupling as claimed in claim 10, wherein the low-friction outer layer is a 5 metallic coating.
12. A coupling as claimed in claim 11, wherein the metallic coating is formed from Indium.

10
13. A coupling as claimed in any one of the preceding claims, wherein the coupling forms part of a valve.
14. A coupling as claimed in claim 13, wherein the valve is a cryogenic valve.

IS
15. A coupling as claimed in claim 13 or claim 14, wherein the first coupling member is a valve seat of the valve and the second coupling member is a body of the valve.
16. A coupling as claimed in any one of the preceding claims, wherein the 20 coupling means is in the form of a screw-thread externally formed on the first coupling member and a complementary screw-thread internally formed on the second coupling member.

(
17. A coupling as claimed in any one of claims I to 15, wherein the coupling means is in the form of a clamp arrangement which, in use, acts to urge the first and second coupling members together.

5
18. A coupling as claimed in any one of the preceding claims, wherein the first and second materials of the first and second coupling members are stainless steel.
19. A coupling as claimed in any one of the preceding claims, wherein the material of the seal element is aluminium.
20. A coupling substantially as hereinbefore described with reference to Figure I or Figure 2 of the accompanying drawings.