WO2005098293A1

WO2005098293A1 - Valve

Info

Publication number: WO2005098293A1
Application number: PCT/GB2005/001254
Authority: WO
Inventors: John Howarth; Richard Bentley; Richard Bateman
Original assignee: Otter Controls Limited
Priority date: 2004-04-08
Filing date: 2005-03-31
Publication date: 2005-10-20
Also published as: GB2412955A; GB2412955B; GB0408055D0

Abstract

A preferred embodiment of the present invention relates to a valve (20, 30, 52, 56, 62) comprising means (22, 24) defining a passageway for the transmission of fluid through the valve, and a thermally responsive operating element (32) which is operable to open the passageway in response to the ambient temperature exceeding a predetermined temperature threshold. The valve of the preferred embodiment may be incorporated in a seating unit for a vehicle.

Description

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Field of the Invention This invention relates to a va_lve, in particular to a thermally responsive valve which is operable to open, for example to relieve pressure in an associated bladder, when the ambient temperature reaches a predetermined threshold. A particularly preferred embodiment of the invention relates to seating, such as that which may be provided in a motor vehicle, which includes such a valve. Embodiments of the present invention, and the problems addressed thereby, will be described hereafter with particular reference to a valve for use in a seat of the type that one might find L-n a motor vehicle. However, it will be appreciated, and should be noted, that the teachings of the present invention may be used in a variety of different applications for the avoidance of a variety of different problems, and as such the following description should be considered merely as being illustrative and not as limiting the scope of the invention in any way. Background to the ?Invention It has long been recognised that seats for motor ve-hicles, such as a motor car for example, should have good ergonomics so that the driver of the vehicle in particular is not distracted or otherwise inconvenienced by an uncomfortable seating position. To this end it is has been proposed, particularly in more expensive vehicles, to provide relatively complicated seats which can be adjusted (often electrically) in a variety of different ways (such as the angle and height of the seat cushion with respect to the floor of the vehicle) in addition to more traditional adjustments such as the distance of the seat from the steering wheel and the angle of the seat bac-krest relative "to the seat cushion. In the pursuit of yet further improved ergonomics it has also been proposed to provide adjustable lumbar supports in the seat backrest, and - particularly for performance vehicles - to provide adjustable seat bac-krest side bolsters. These adjustable lumbar supports and seat backrest side bolsters (and in some cases other components of the seating unit) are typically pneumatic components that can be adjusted in size by inflating or deflating a bladder provided at an appropriate location within the body of the seating unit. Illustrative seat backrests with integral pneumatic lumbar supports are disclosed in -International PCT Patent Application Nos. WO 98/42234 and WO 99/48720. Fig. la is an illustrative view, in longitudinal cross-section, of part of a seat back rest 1. As shown, the backrest comprises a structural member 3

(such as a plastic or metal backplate) over which inner 5 and outer 7 layers of compressible foam material are provided with an inflatable bladder 9 (shown deflated) sandwiched therebetween. The outer foam layer is covered by a fabric or leather seat cover 11 on which the user sits in use. The user, by operating appropriate controls (not shown), can inflate the bladder 9 to a user selectable extent to thereby increase the degree of lumbar (or other) support provided by the backrest. As shown in Fig. lb, inflating the bladder 9 causes the seat cover 11 to bulge as a result of the outer foam layer 7, in particular, being compressed against the inside of the seat cover 11. The user is also able, at their option, to deflate an inflated bladder to decrease the degree of lumbar support provided by the backrest. Whilst this arrangement functions adequately to enable a user to adjust the extent of lumbar support - for example - provided by the backrest, a problem exists in that it is possible for the foam to permanently set in a compressed shape if the bladder should be inflated when the temperature within the vehicle rises above a critical value (as might happen, for example, if the vehicle is in a hot climate or left for a period of time in the sunshine). As shown in Fig. lc, if the foam should take on a permanent set, subsequent deflation of the bladder 9 will leave a persistent depression 13 in the outer foam layer 7, in particular. The effect of this depression is that subsequent inflation of the bladder 9 merely serves to fill the depression without providing additional lumbar support. Whilst it is commonplace to provide a pressure relief valve in the inflation system of such seating units (to prevent over-inflation of the bladder), there is currently no means for avoiding the problem outlined above. The only solution, once the problem has occurred, is to replace the seats at considerable expense and inconvenience to the user or owner of the vehicle. The present invention has been conceived with the particular aim of providing a means, preferably a relatively inexpensive means, for avoiding such problems. Statement of the Invention To this end, a presently preferred embodiment of the invention provides a valve comprising means defining a passageway for the transmission of fluid through the valve, and a thermally responsive operating element which is operable to open the passageway in response to the ambient temperature exceeding a predetermined temperature threshold. This arrangement is advantageous in that as the operating element itself is thermally responsive, the cost of the valve can be reduced significantly as compared to relatively complex electronic systems that include a temperature sensor, control logic and means for opening a passageway through a valve. Other preferred features and advantages of the preferred embodiment will become apparent from the following description and accompanying drawings, which are provided merely by way of illustrative example. Brief Description of the Drawings Preferred embodiments of the present invention will now be described with reference to the accompanying drawings, in which: Figs, la to lc are illustrative representations of part of a previously proposed seating unit; Figs. 2a to 2c are - respectively - isometric, exploded and cross- sectional views of a valve in accordance with a first embodiment of the present invention; Figs. 3a to 3c are - respectively - isometric, exploded and cross- sectional views of a valve in accordance with a second embodiment of the present invention; Figs. 4a to 4c are - respectively - isometric, exploded and cross- sectional views of a valve in accordance with a third embodiment of the present invention; Figs. 5a to 5c are - respectively - isometric, exploded and cross- sectional views of a valve in accordance with a fourth embodiment of the present invention; Figs. 6a to 6c are - respectively - isometric, exploded and cross- sectional views of a valve in accordance with a fifth embodiment of the present invention; Figs. 7a and 7b illustrate the different operating states of the valve depicted in Figs. 2a to 2c; and Figs. 8a and 8b illustrate the different operating states of the valve depicted in Figs. 3a to 3c. Detailed Description of the Preferred Embodiment Referring collectively to Figs. 2a to 2c there is depicted - respectively - isometric, exploded and cross-sectional views of a valve 20 in accordance with the first embodiment of the invention. As depicted, the valve 20 comprises a housing (for example of moulded plastics material) that includes a tubular inlet part 22 and an outlet part 24. The inlet part 22 is provided with a stepped outer surface 26 to facilitate its insertion in an outlet pipe leading, for example, from a bladder of the type depicted in Figs, la to lc. The outlet part 24 includes a depression 28 (Fig. 2b), the base 29 of which forms a valve seat for a rubber seal 30 which is arranged to close the central bore of the tubular inlet part when biased against the valve seat by an operating element 32. The peripheral wall 34 of the depression 32 is provided with a plurality of operating element restraints 36 (against the underside of which the operating element bears in use) and a rib 38 which functions to retain the operating element in the depression. The peripheral wall 34 also includes a number of exhaust ports 40 through which fluid under pressure is able to escape when the biasing force provided to the seal 30 by the operating element 32 is removed. In the preferred embodiment, the operating element comprises a snap- acting dished bimetallic disk which is operable to snap from the state depicted in Fig. 2c (referred to hereafter as its "cold state") to an oppositely dished shape (depicted in Fig. 7b and referred to hereafter as its "hot state") when the ambient temperature exceeds a predetermined threshold temperature, for example a temperature approaching that at which the foam in the seat might acquire a permanent set if compressed. As depicted in Fig. 2c (and indeed in Fig. 7a), in its cold state the rim of the operating element bears against the underside of the restraints 36 (one of which is visible in each of these figures) and rib 38 to press the seal 30 against the valve seat 29 and close the valve. When the ambient temperature exceeds the aforementioned threshold temperature, the operating element 32 assumes its hot state by reversing its curvature, and the force applied by the operating element 32 to bias the seal 30 against the valve seat 29 is removed. The seal 30 can then move away -from the valve seat to allow fluid under pressure within an expanded bladder, for example, connected to the inlet part 22 to exhaust through the central bore of the inlet part 22 and out of the aforementioned exhaust ports 40 formed in the peripheral wall 34 of the outlet part 24 of the valve 20. By virtue of this arrangement the pressure in a bladder, for example, provided within a seat can be relieved, thereby avoiding the aforementioned problem whereby the foam in the seat can take on a permanent set if it is compressed (as it would be if the bladder were inflated) as the ambient temperature rises above the aforementioned threshold. If the ambient temperature should drop to below the aforementioned threshold temperature (as might happen if the climate control system of the car should be activated), the operating element will revert from the hot state depicted in Fig. 7b to the cold state depicted in Fig. 7a, and the seal will once more close the valve to fluid transmission thereby allowing the user to inflate the bladder, for example, should they wish to. Admittedly, use of a valve as described in a seating unit will require the user to readjust the seat of the vehicle if the valve should operate, and whilst this would be of some inconvenience to the user it is considerably less inconvenient (and expensive) than having to replace the seats of the vehicle. Referring collectively to Figs. 3a to 3c, there is depicted a valve 30 according to a second embodiment of the present invention. The valve 30 is superficially similar to that of the first embodiment, and common features between the two (and indeed the other embodiments described herein) will for efficacy be referenced with the same reference numerals. The principal difference between the valves of the two embodiments, as will be appreciated hereafter, is that in the first embodiment the pressure exerted by an inflated bladder, for example, connected to the valve provides a force wliich tends to drive the seal away from the valve seat to open the valve, and this force tends to lower the temperature at which the operating element changes from its cold state to its hot state. In the second embodiment described below, the pressure exerted by an inflated bladder, for example, coupled to the valve provides which tends to drive the seal towards the valve seat, and as a consequence the operating element needs to generate a compensating force before it can change from its cold state to its hot state to open the valve- that compensating force tending to raise the temperature at which the operating element moves from its cold state to its hot state. These factors need to be taken into account when determining the threshold temperature at which the operating element will operate, so that the valve opens at the required temperature. The principal external difference between the valve 30 of this embodiment and the valve 20 of the first embodiment, is that the outlet part 24 includes a lid 41 that is formed with an exhaust port 42 therein instead of a plurality of exhaust ports being provided in the peripheral wall 34 of the outlet part 24. The lid 41 is bonded or otherwise affixed to the outlet part 24 once the internal components of the valve have been arranged therein. The lid 41 includes a circumferential rim 44 which is spaced from the peripheral edge of the lid so that it closely abuts against the inside of the peripheral wall 34 of the outlet part 24 when the lid is located on the outlet part 24. As depicted in Fig. 3 c, the rim 44 extends partway into the depression 28 to provide a surface against which the operating element 32 can bear when it snaps from its cold state to its hot state in the event of the ambient temperature exceeding the aforementioned threshold temperature. The base 29 of the depression 28 in this embodiment does not form a valve seat, that function instead being provided by an inner surface 46 of the lid. Rather, the base 29 of the depression provides a surface against which the operating element bears in its cold state to force the seal against the valve seat formed by the aforementioned inner surface 46 of the lid 41 and thereby close the valve. To facilitate the flow of fluid round the operating element 32 and seal 30 when the operating element snaps from its cold state to its hot state to open the valve, the base 29 of the depression is provided with a series of radial channels 48. Fluid flow through the valve when the valve opens may further be enhanced by forming one or more channels (not shown) in the circumferential rim 44 on the underside of the lid 41. As depicted in Fig. 3c, the operating element 32 of this embodiment is arranged so that in its cold state it is oppositely dished to the operating element of the first embodiment. The operating element 32 is also provided with an aperture through which a pip 50 formed on the seal 30 is located to attach the seal 30 to the operating element 32. Effectively, the pip 50 couples the seal 30 to the operating element 32 for movement in union therewith, thereby causing the seal 30 to be positively withdrawn from the valve seat 46 when the operating element 32 moves from its cold state to its hot state. As before, the operating element is preferably a snap-acting dished bimetallic disk which is operable to snap from the state depicted in Figs. 3c and 8a (referred to hereafter as its "cold state") to an oppositely dished shape (depicted in Fig. 8b and referred to hereafter as its "hot state") when the ambient temperature (for example the temperature of the interior of a car) exceeds a predetermined threshold temperature, in particular a temperature approaching that at which the foam in the seat might acquire a permanent set if compressed. As shown in Figs. 3c and 8a, in its cold state the operating element 32 is configured to bear upon the base 29 of the depression to drive the seal against the valve seat formed by the inner surface 46 of the lid to thereby close the valve to fluid transmission therethrough. When the ambient temperature reaches the aforementioned threshold, the operating member snaps to its hot state (i.e. a state as depicted in Fig. 8b where the element is oppositely dished to that depicted in Fig. 3c), and positively withdraws the seal 30 from the valve seat formed by the inner surface 46 of the lid. Fluid under pressure in a bladder, for example, connected to the valve can then move from the inlet part, round the periphery of the operating element and seal, and out of the exhaust port 42 formed in the lid 41. As before, if the ambient temperature should drop to below the aforementioned threshold, the operating element will revert to its cold state thereby closing the valve once more. Referring now to Figs. 4a to 4c, there is depicted a valve 52 according to a third embodiment of the present invention which is similar to the valve 20 of the second embodiment in that the pressure exerted by an inflated bladder, for example, connected to the inlet part 22 of the valve provides a force that tends to close the valve. The principal difference between the valve of this embodiment and that of the second embodiment, is that in this third embodiment an o-ring 54 is located in a groove (not shown) formed in the aforementioned inner surface of the lid 40 about the periphery of the exhaust port 42, the operating element 32 bearing against the o-ring 54 in its cold state to close the valve. As before, the operating element is preferably a snap-acting dished bimetallic disk which is operable to snap from the state depicted in Figs. 4c

(referred to hereafter as its "cold state") to an oppositely dished shape (referred to hereafter as its "hot state") when the ambient temperature (for example the temperature of the interior of a car) exceeds a predetermined threshold temperature, in particular a temperature approaching that at which the foam in the seat might acquire a permanent set if compressed. As mentioned above, the operating element 32 in its cold state bears against and partly compresses the o-ring 54 to seal the inlet 22 from the exhaust port 42 in the lid 40 thereby closing the valve. When the ambient temperature exceeds the aforementioned threshold, the operating element 32 changes to its oppositely dished curved state (as shown in Fig. 8b) and withdraws from abutment against the o-ring 54 to open the valve. As before, the operating element 32 reverts back to its cold state thereby closing the valve when the ambient temperature drops below the aforementioned threshold. Referring now to Figs. 5a to 5c, there is depicted a valve 56 according to a fourth embodiment of the present invention which is similar to the valve 20 of the first embodiment in that the pressure exerted by an inflated bladder, for example, connected to the inlet part 22 of the valve provides a force on the seal that tends to move the seal away from the valve seat to open the valve. lh this embodiment, the outlet part 24 includes a lid 41 that is formed with an exhaust port 42 therein instead of a plurality of exhaust ports being provided in the peripheral wall 34 of the outlet part 24. The lid 41 is bonded or otherwise affixed to the outlet part 24 once the internal components of the valve have been arranged therein. Instead of the circumferential rim 44 of the second embodiment (as shown in Figs. 4a to 4c), the lid 41 of this embodiment includes a plurality of circumferentially spaced depending tongues 58 which extend from the underside of the lid 41 through the depression 28 formed in the outlet part 24 towards the base 29 of the depression 28, the base 29 forming the valve seat against which the seal 30 is pressed by the operating element 32 in its cold state to close the valve. An advantage of this arrangement is that the tongues include intervening spaces 60 which facilitate the flow of fluid through the valve from the inlet part 22 to the exhaust port 42 in the lid affixed to the outlet part 24 when the operating element is in its hot state and has moved to remove the force biasing the seal 30 against the valve seat 29. As with the other embodiments, the operating element is preferably a snap-acting dished bimetallic disk wliich is operable to snap from the state depicted in Fig. 5c (referred to hereafter as its "cold state") to an oppositely dished shape such as that depicted in Fig. 7b (referred to hereafter as its "hot state") when the ambient temperature (for example the temperature of the interior of a car) exceeds a predetermined threshold temperature, in particular a temperature approaching that at which the foam in the seat might acquire a permanent set if compressed. As before, the operating element 32 reverts back to its cold state to press the seal against the valve seat thereby closing the valve when the ambient temperature drops below the aforementioned threshold. Figs. 6a to 6c are illustrative views of a valve 62 in accordance with a fifth embodiment of the present invention. The valve 62 of this embodiment is similar to that of the first and fourth embodiments in that the pressure exerted by an inflated bladder, for example, connected to the inlet part 22 of the valve provides a force that tends to open the valve. This apart, the valve 62 of this embodiment is fundamentally different in that the outlet 24 and tubular inlet 22 parts are manufactured as discrete components. ?ln the preferred arrangement the inlet part 22 is moulded from plastics material, and the outlet part is formed of a suitable elastomeric material such as rubber. As shown in Fig. 6b, the inlet part tapers outwardly in discrete steps from an inlet 64 to an enlarged shoulder 66 which is formed, on its opposite face with a series of radial channels 48 to facilitate the movement of fluid through the valve when the valve is opened. The shoulder 66 of the inlet part is push-fitted in a lipped depression

68 formed in one side of the outlet part. The operating element 32 can be likewise push-fitted in a similar lipped depression 70 formed in the other side of the outlet part 24 - the two depressions being in communication with one another by virtue of several through-holes 72 formed in the elastomeric outlet part 24. As shown in Fig. 6b, the operating element includes a central aperture 74 which locates on a pip 76 formed in the lipped depression 70 when the operating element is fitted therein. ]?n its cold state, as depicted in Fig. 6c, the operating element 32 seals against the elastomeric outlet part by virtue of the location of the central aperture 74 on the pip 76, and by virtue of the abutment of the operating element peripheral rim 78 with the underside of the lip 80 (the force of that abutment being enhanced by the pressure exerted by an inflated bladder, for example, connected to the inlet part 22). When the ambient temperature exceeds that at which the operating element switches to its hot state, the central aperture of the operating element moves away from the pip and fluid contained within an inflated bladder, for example, connected to the inlet part of the valve can exhaust through the valve via the tubular inlet part 22, the through-holes 72 and the central aperture 74 in the operating element. As with the other embodiments, the operating element is preferably a snap-acting dished bimetallic disk which is operable to snap from the state depicted in Fig. 6c (referred to hereafter as its "cold state") to an oppositely dished shape such as that depicted in Fig. 7b (referred to hereafter as its "hot state") when the ambient temperature (for example the temperature of the interior of a car) exceeds a predetermined threshold temperature, in particular a temperature approaching that at which the foam in the seat might acquire a permanent set if compressed. As before, the operating element 32 reverts back to its cold state to close the valve when the ambient temperature drops below the aforementioned threshold. As will be appreciated from the above, the teachings of the present invention provide an eminently simple and inexpensive means to avoid the type of seat damage aforementioned. The teachings of the present invention may also advantageously be employed in a variety of different applications. As such whilst various preferred embodiments of the invention have been described above in detail with particular reference to a vehicle seat, the scope of the present invention should not be taken to be limited solely to application of pressure relief valves to seating. It is also the case that modifications and alterations may be made to the particular embodiments described herein without departing from the scope of the present invention as claimed. Furthermore, whilst various combinations of features have been presented hereafter in the claims, it should be noted that the scope of the present invention extends to any combination of features described herein irrespective of whether that combination has been explicitly enumerated in the accompanying claims.

Claims

CLAIMS 1. A valve comprising means defining a passageway for the transmission of fluid through the valve, and a thermally responsive operating element w-faich is operable to open the passageway in response to the ambient temperature exceeding a predetermined temperature threshold

2. A valve according to Claim 1, wherein the operating element comprises a dished bimetallic actuator, the bimetallic actuator being operable to change from a cold state to a hot state in response to the ambient temperature exceeding the predetermined temperature threshold, said dished bimetal being oppositely dished in said cold and hot states.

3. A valve according to Claim 2, wherein the bimetallic actuator is operable to snap between said cold state and said hot state, and said hot state and said cold state.

4. A valve according to Claim 2 or 3, wherein the operating element is arranged so that a positive pressure applied to an inlet part of the valve provides a force that assists the opening of the valve.

5. A valve according to Claim 2 or 3, wherein the operating element is arranged so that a positive pressure applied to an inlet part of the valve provides a force that hinders the opening of the valve.

6. A valve according to Claim 4 or 5, wherein said means defining the passageway comprises said inlet part, and an outlet part integrally formed with said inlet part.

7. A valve according to Claim 4, wherein said means defining the passageway comprises said inlet part and a separate outlet part, the inlet and outlet parts being arranged to be coupled together to define said passageway.

8. A valve according to Claims 4 and 6, comprising a seal, said seal being provided in a depression formed in said outlet part.

9. A valve according to Claim 8, wherein the seal comprises a rubber disk.

10. A valve according to Claim 8 or 9, wherein a base of said depression forms a valve seat, said base including an aperture through which fluid can flow from the inlet part when the valve is open.

11. A valve according to Claim 10, wherein the bimetallic actuator is operable in its cold state to exert a force on the seal to press the seal against the valve seat to close said aperture, and hence the passageway through the valve.

12. A valve according to Claim 11, wherein the force exerted by the bimetallic actuator on the seal is removed when said actuator changes to said hot state thereby to allow the seal to move away from said valve seat to open said aperture, and hence the passageway through the valve.

13. A valve according to Claim 11 or 12, wherein the outlet part includes one or more exhaust ports in a peripheral wall of said depression for exhausting fluid when said seal is able to move away from said valve seat.

14. A valve according to Claim 13, wherein the peripheral wall of said depression includes a plurality of inwardly projecting actuator retaining tabs.

15. A valve according to Claim 14, wherein at least a rim of the bimetallic actuator is configured to bear upon the underside of each of said actuator retaining tabs when in said cold state to provide the force for pressing the seal against the valve seat.

16. A valve according to Claim 11 or 12, wherein said valve comprises a lid for covering said depression once the bimetallic actuator and seal have been located therein.

17. A valve according to Claim 16, wherein the lid comprises one or more exhaust ports for exhausting fluid when said seal is able to move away from said valve seat.

18. A valve according to Claim 16 or 17, wherein at least a rim of the bimetallic actuator is configured to bear upon the underside of said lid, when affixed to said outlet part, to provide in said cold state the force for pressing the seal against the valve seat.

19. A valve according to any of Claims 16 to 18, wherein the underside of said lid includes a circumferential wall comprised of a plurality of spaced depending tongues which are arranged to extend into said depression, preferably into abutment with said valve seat, when the lid is located on said outlet part to cover said depression.

20. A valve according to Claim 18 and 19, wherein the bimetallic element and seal fit within said circumferential wall when the lid is located on the outlet part.

21. A valve according to Claim 20, wherein the spaces between said tongues provide a means for facilitating fluid flow round the periphery of said actuator and seal to said one or more exhaust ports when the bimetallic actuator is in said hot state and said seal is free to move to open the valve.

22. A valve according to any of claims 16 to 21, wherein said lid is adhered or otherwise affixed, for example by welding, to said outlet part to cover said depression once the bimetallic actuator and seal have been located therein.

23. A valve according to Claims 4 and 7, wherein the outlet part is of a resilient material, such as a rubber elastomer.

24. A valve according to Claim 23, wherein the outlet part includes means for enabling the inlet part to be push-fit coupled thereto.

25. A valve according to Claim 23, wherein the coupling means comprises a depression formed in said outlet means, the depression including a lip that is arranged to fit over a shoulder formed in said inlet part when the inlet part is coupled to the outlet part.

26. A valve according to any of Claims 23 to 25, wherein the outlet part includes a lipped depression for accommodating the bimetallic actuator.

27. A valve according to Claim 26, wherein the bimetallic actuator includes a central aperture, and the lipped depression includes a central pip on which the aperture in the actuator locates when the bimetallic actuator is in its cold state and is accommodated within the lipped depression.

28. A valve according to Claim 27, wherein at least the rim of the actuator is arranged to bear on the underside of the lip of said actuator depression when the actuator is in said cold state, the abutment of the rim with the lip and the aperture with the pip together serving to close the fluid passageway through the valve.

29 A valve according to Claim 27 or 28, wherein the aperture in the bimetallic aperture which locates on the pip when the actuator is in its cold state functions as an exhaust port when the actuator is in its hot state.

30. A valve according to Claim 25 and any of Claims 26 to 29, wherein the outlet part includes one or more through-holes between said coupling depression and said actuator depression, fluid flow through the valve being permitted when the actuator is in said hot state and the actuator aperture is no longer located on said pip.

31. A valve according to Claim 30 and any of Claims 25 to 29 when dependent on Claim 24, wherein the inlet part includes a face bounded by said shoulder, the face including a plurality of channels for facilitating fluid flow through the through-holes when the valve is open.

32. A valve according to Claims 5 and 6, wherein the outlet part includes a depression for accommodating the bimetallic actuator.

33. A valve according to Claim 32, wherein said v^alve comprises a lid for covering said depression once the bimetallic actuator has been located therein.

34. A valve according to Claim 32 or 33, wherein the lid includes one or more exhaust ports through which fluid may be exhausted when the valve is open.

35. A valve according to Claim 33 or 34, wherein the underside of said lid is provided with a circumferential wall that is configured to extend partway into said depression when the lid is affixed to said outlet part.

36. A valve according to any of Claims 32 to 35, wherein said depression in said outlet includes a base surface on which at least a rim of the bimetallic actuator is arranged to bear when the actuator is in its cold state.

37. A valve according to Claim 36, wherein said base surface includes a plurality of radial channels to facilitate fluid flow through the valve when the valve is open.

38. A valve according to any of Claims 33 to 37, wherein the underside of said lid forms a valve seat.

39. A valve according to Claim 38 when dependent on Claim 34, comprising a seal, the bimetallic actuator being operable in its cold state to exert a force on the seal to press the seal against the valve seat to close said one or more exhaust ports, and hence the passageway through the valve.

40. A valve according to Claim 39, comprising means for coupling the actuator to the seal so that the seal moves with the actuator when the actuator changes from its cold state to its hot state, and from its hot state to its cold state.

41. A valve according to Claim 40, wherein the coupling means comprises a pip on the seal which can tightly locate in an aperture formed in the bimetallic actuator.

42. A valve according to Claim 40 or 41, wherein the seal is positively withdrawn from abutment with said valve seat when the actuator changes to the hot state thereby to open said aperture, and hence the passageway through the valve.

43. A valve according to any of Claims 35 to 37 when dependent on Claim 34, comprising a resilient seal affixed to the underside of said lid, the seal encompassing within its periphery said one or more exhaust ports.

44. A valve according to Claim 43, wherein said resilient seal comprises an o-ring located in a circular groove formed in the underside of said lid.

45. A valve according to Claim 44, wherein the bimetallic actuator is operable in its cold state to exert a force on the o-ring to form a seal between the o-ring and the bimetallic actuator, said seal preventing the release of fluid from the valve.

46. A valve according to Claim 45, wherein the bimetallic actuator is operable to move out of abutment with said o-ring in its hot state to open the valve.

47. A vehicle seat comprising a bladder which is inflatable by a user to provide a user-selectable degree of support, and a valve according to any preceding claim which is configured to open to relieve pressure in the bladder in the event that the ambient temperature should rise above a predetermined threshold.

48. A thermally responsive valve comprising a bimetallic actuator which is operable to snap from a first shape to a second shape when the ambient temperature exceeds a predetermined threshold, the actuator being configured to open the valve at a temperature above the threshold, and to keep the valve closed at a temperature below the threshold.

49. A valve substantially as hereinbefore described with reference to the accompanying drawings.

50. A vehicle seat substantially as hereinbefore described with reference to the accompanying drawings.