ACTUATION UNIT AND VALVE ASSEMBLY COMPRISING THE SAME

Abstract

A valve assembly including a valve arranged to move between open and closed positions by rotating an operating member about an axis is provided. An actuation unit includes a torsion spring, a trigger member, and a driving member. The driving member engages with the operating member to drive rotation of the same. The torsion spring applies a first torque to the driving member around the axis in a first rotational direction. An external second torque opposite the first torque resets the valve to the open position in which the driving member is held by a latching mechanism. The latching mechanism is arranged to hold the driving member only when the valve is in the open position. An external force applied to the trigger member releases the driving member from the latching mechanism, the first torque thereby rotating the driving member to mechanically bias said valve to the closed position.

Claims

1. A valve assembly comprising: a valve having an open position and a closed position, said valve being arranged to move between the open position and the closed position by rotating an operating member of the valve about an axis; and an actuation unit comprising a torsion spring, a trigger member, and a driving member, said driving member being arranged to engage with the operating member of the valve to drive rotation of the operating member, wherein the torsion spring applies a first torque to the driving member around the axis in a first rotational direction; wherein an external second torque applied opposite to the first torque resets the valve to the open position in which the driving member is held by a latching mechanism, thereby resisting the first torque of the torsion spring, said latching mechanism being arranged to hold the driving member only when the valve is in the open position; and wherein an external force applied to the trigger member releases the driving member such that it is no longer held by the latching mechanism, the first torque thereby rotating the driving member in the first rotational direction to drive rotation of the operating member and mechanically bias said valve to the closed position.

2. The valve assembly as claimed in claim 1, wherein the external force required to release the driving member is less than the force that would be required to manually close the valve.

3. The valve assembly as claimed in claim 1, wherein the external force applied to the trigger member is a non-rotary force.

4. The valve assembly as claimed in claim 1, wherein the trigger member comprises a button, wherein the driving member is released when the button is pressed.

5-8. (canceled)

9. The valve assembly as claimed in claim 1, wherein the trigger member comprises a pull tab.

10. The valve assembly as claimed in claim 9, wherein the pull tab comprises a latch member against which the driving member is held when held by the latching mechanism, wherein a lateral movement of the pull tab releases the driving member.

11-13. (canceled)

14. The valve assembly as claimed in claim 1, wherein the driving member is centred on the axis of the valve.

15. The valve assembly as claimed in claim 1, wherein the driving member is seated inside the torsion spring.

16. The valve assembly as claimed in claim 1, wherein the driving member comprises a substantially cylindrical component with a ridged portion arranged to hold the driving member in position when latched.

17. (canceled)

18. The valve assembly as claimed in claim 1, wherein the latching mechanism comprises a tab that, when latched, is held in abutment against a stop face; wherein the tab is provided on the trigger member, and wherein the trigger member mechanically engages the driving member such that both the trigger member and driving member rotate about the axis of the valve together.

19-25. (canceled)

26. The valve assembly as claimed in claim 1, wherein the valve is a quarter-turn valve, optionally wherein the valve is a ball valve.

27-28. (canceled)

29. The valve assembly as claimed in claim 1, arranged such that an external third torque in the first rotational direction closes the valve, optionally wherein the external third torque must exceed a threshold amount of force to overcome a resistance of the driving member when latched before the valve can be forced closed.

30. (canceled)

31. The valve assembly as claimed in claim 1, wherein the torsion spring is invertible, such that the respective directions of the first and second rotational directions may be swapped.

32-34. (canceled)

35. The valve assembly as claimed in claim 1, wherein the actuation unit comprises an engagement portion arranged to engage with a pipe, wherein the engagement portion comprises a hinged portion.

36. An actuation unit for a valve assembly, the actuation unit comprising a torsion spring, a trigger member, and a driving member, said driving member being arranged to engage with an operating member of a valve to drive rotation of the operating member, wherein the torsion spring applies a first torque to the driving member around the axis in a first rotational direction; wherein an external second torque applied opposite to the first torque resets the valve to an open position in which the driving member is held by a latching mechanism, thereby resisting the first torque of the torsion spring, said latching mechanism being arranged to hold the driving member only when the valve is in the open position; and wherein an external force applied to the trigger member releases the driving member such that it is no longer held by the latching mechanism, the first torque thereby rotating the driving member in the first rotational direction so as to drive rotation of the operating member and mechanically bias the valve to the closed position.

37-40. (canceled)

41. An actuation unit for a valve assembly, the actuation unit comprising a torsion spring, a trigger member, and a driving member, said driving member being arranged to engage with an operating member of a valve to drive rotation of the operating member, wherein the torsion spring applies a first torque to the driving member around the axis in a first rotational direction; wherein an external second torque applied opposite to the first torque resets the valve to an open position in which the driving member is held by a latching mechanism, thereby resisting the first torque of the torsion spring, said latching mechanism being arranged to hold the driving member when the valve is in the open position; and wherein an external force applied to the trigger member releases the driving member such that it is no longer held by the latching mechanism, the first torque thereby rotating the driving member in the first rotational direction so as to drive rotation of the operating member and mechanically bias the valve to the closed position; the actuation unit further comprising a sacrificial element arranged to release the driving member such that it is no longer held by the latching mechanism.

42. The actuation unit as claimed in claim 41, wherein the sacrificial element comprises a glass bulb, and wherein the latching mechanism comprises a bulb retainer that, in normal operation, is held in abutment between the glass bulb and the driving member

43-46. (canceled)

47. The actuation unit of claim 36, wherein the trigger member comprises a button, and wherein the driving member is released when the button is pressed.

48. A system comprising: (i) the actuation unit of claim 36; (ii) a Bowden cable connected to the actuation unit to apply the external force to the trigger member; and (iii) a remote terminal comprising a button; wherein, when a user presses the button, the Bowden cable is pulled so as to trigger release of the latching mechanism, thereby closing the valve.

49. The valve assembly of claim 1, further comprising a Bowden cable connected to the actuation unit to apply the external force to the trigger member.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Certain embodiments of the present invention will now be described with reference to the accompanying drawings, in which:

[0065] FIGS. 1A and 1B are schematic drawings of a quarter-turn valve;

[0066] FIGS. 2A and 2B are cross-sectional drawings of the valve of FIGS. 1A and 1B;

[0067] FIGS. 3A and 3B are schematic drawings that show an actuation unit with a top button in accordance with an embodiment of the present invention including the handle used to operate the valve;

[0068] FIG. 4 is an exploded view of the actuation unit in accordance with an embodiment of the present invention;

[0069] FIG. 5 is a further exploded view of the actuation unit of FIG. 4;

[0070] FIG. 6 is a cross-sectional view of the actuation unit of FIG. 4 that shows the torsion spring;

[0071] FIGS. 7A and 7B are schematic drawings that illustrate operation of the button used to trigger the actuation unit of FIG. 4;

[0072] FIG. 8 is a cross-sectional drawing that shows a mechanism that allows for the valve to be closed manually;

[0073] FIGS. 9A-E are schematic drawings illustrating operation of the actuation unit of FIG. 4;

[0074] FIGS. 10A-D are further schematic drawings illustrating operation of the actuation unit;

[0075] FIG. 11 is a cross-sectional drawing that shows how the torsion spring drives the arbor;

[0076] FIG. 12 is a cross-sectional drawing showing a fire protection mechanism within the actuation unit;

[0077] FIGS. 13A-C are schematic drawings illustrating operation of sacrificial fire protection mechanisms;

[0078] FIGS. 14A and 14B are schematic diagrams showing an alternative sacrificial triggering mechanism;

[0079] FIGS. 15A-C are schematic drawings that show an actuation unit with a side button in accordance with a further embodiment of the present invention;

[0080] FIGS. 16A-C are further schematic drawings illustrating operation of the actuation unit of FIGS. 15A-C;

[0081] FIG. 17 is a schematic drawing that shows an actuation unit with a pull-tab trigger mechanism in accordance with a further embodiment of the present invention;

[0082] FIGS. 18A-D are schematic drawings that show an actuation unit with a Bowden cable trigger mechanism in accordance with an embodiment of the present invention;

[0083] FIGS. 19A and 19B are cross-sectional drawings showing a remote terminal for use with the actuation unit of FIGS. 18A-D;

[0084] FIGS. 20A-C are cross-sectional drawings that show an alternative mechanism that allows for the valve to be closed manually;

[0085] FIGS. 21A-C are schematic drawings of an actuation unit with a sacrificial triggering mechanism that uses a frangible glass bulb in accordance with a further embodiment of the present invention; and

[0086] FIGS. 22A-B are further schematic drawings illustrating the operation of the sacrificial glass bulb triggering mechanism of FIGS. 21A-C.

DETAILED DESCRIPTION

[0087] FIGS. 1A and 1B are schematic drawings of a quarter-turn valve 2, while FIGS. 2A and 2B are cross-sectional drawings of the valve 2 of FIGS. 1A and 1B. In particular, the valve 2 shown is a quarter-turn ball valve, as outlined in further detail below.

[0088] The valve 2 comprises a valve housing 4, with two fluid apertures 6, 8 which allow ingress of a fluid, i.e. a liquid or a gas, into the valve 2. An operating member 10 is arranged to rotate a quarter turn between an ‘on’ position (as shown in FIGS. 1A and 2A) in which fluid may flow freely through the valve 2, and an ‘off’ position (as shown in FIGS. 1B and 2B) in which the fluid is prevented from flowing through the valve 2. Typically, a handle (not shown) is attached to a stem 11, which may be threaded, such that rotation of the handle rotates the stem 11 about an axis, thereby rotating a ball 14 within the valve housing 4 about the axis of the stem 11.

[0089] The ball 14 has a hollow cylinder 15 running through it, such that in the on position, the flow axis of the hollow cylinder 15 is aligned with the axis of the valve 2 such that fluid may pass through the valve 2. In the off position, however, the flow axis of the hollow cylinder 15 is perpendicular to the flow axis of the valve 2, such that there is no fluid flow path, thereby preventing flow of the fluid.

[0090] It will be appreciated that intermediate positions between the on and off positions may reduce but not completely inhibit fluid flow, however generally an emergency valve such as an emergency domestic gas shut off valve is either ‘on’ or ‘off’, with intermediate positions being undesirable for safety reasons well understood by those skilled in the art.

[0091] FIGS. 3A and 3B are schematic drawings that show an actuation unit 16 with a top button 20 in accordance with an embodiment of the present invention including the handle used to operate the valve 2. The internal construction of the actuation unit 16 may be readily understood with reference to FIGS. 4 to 6. Briefly, FIGS. 4 and 5 provide exploded views of the actuation unit 16, and FIG. 6 is a cross-sectional view of the actuation unit 16.

[0092] The actuation unit 16 is constructed from a housing 18 fitted a lid 19, a top button 20 (i.e. a trigger member) including a button inner 25 which is positioned within, and is movable vertically relative to, a button housing 21. The button housing 21 is also moveable vertically relative to the housing 18, as explained in further detail below.

[0093] A hinged portion 17 is positioned at the bottom of the actuation unit 16, and ‘hinges’ away from the housing 18. This hinged portion 17 acts as a ‘strap’ such that, where the valve 2 is connected in-line with a pipe (not shown), the hinged portion 17 allows the actuation unit 16 to be clamped around the valve 2 and affixed to the pipe. This hinged portion 17 may be ‘double hinged’, such that the strap may open in either direction, as different installations may require that the strap open one direction or the other in order to fit it around the pipe. It will of course be appreciated that other arrangements are possible, e.g. the hinged portion 17 could instead be a wholly separate piece that is screwed or bolted to the housing 18 once the actuation unit 16 is in place.

[0094] The handle 22 may be supplied as part of the actuation unit 16 or may be an existing handle associated with the valve 2 which is removed when the actuation unit 16 is fitted, and then re-attached once the actuation unit 16 is in place. A tab-shaped protrusion 23 extends from an outer surface of the button housing 21 and is arranged to latch against the housing 18 of the actuation unit 16, as outlined in further detail below.

[0095] The button housing 21 engages with the operating member 10 of the valve 2, specifically with the stem 11, via an arbor 36 as outlined in further detail below. It will be appreciated that in other embodiments, the button housing 21 may additionally or alternatively engage with the handle 22 (again, via the arbor 36 outlined below) which, in turn, engages the stem 11.

[0096] Two side tabs 24 extend from the button housing 21, though these could form part of the handle 22 in some embodiments, e.g. the handle 22 and side tabs 24 could be of integral construction. An ‘on’ indicator 26 and an ‘off’ indicator 28 are located on the upper face of the lid 19. Depending on whether the valve 2 is in the open or closed position, only one of these indicators 26, 28 is visible at a time, the other indicator 26, 28 being covered by the side tabs 24. This allows a user to easily see at a glance the current operating state of the valve 2, i.e. whether it is open or closed. In the illustrated embodiment, the ‘on’ indicator 26 and an ‘off’ indicator 28 are the words ‘ON’ and ‘OFF’ respectively, however it will be appreciated that these indicators may be any other form of verbal or symbolic indicator, for example colors, symbols, pictograms, words, letters, ticks/crosses, etc. as appropriate.

[0097] As will be explained in further detail below, pushing the button 20 in the downward direction 30 (i.e. vertically relative to the button housing 21) releases a driving member from a latch, causing the driving member to force the valve 2 from the open position (see FIGS. 1A, 2A, and 3A) to the closed position (see FIGS. 1B, 2B, and 3B), by rotating the operating member 10 of the valve 2 around its axis, i.e. in a rotational direction 32. The mechanism that achieves this may be readily understood by reference to FIGS. 4, 5, and 6.

[0098] Within the housing 18 is located a torsion spring 34 and an arbor 36 (i.e. a driving member). The torsion spring 34 has a tab 38a, 38b at each end of the spring 34. The outermost tab 38a is, when assembled, held in place in a slot 40 of the housing 18. The housing 18 may be provided with a number of these slots 40, such that the ‘built in’ torsion of the torsion spring 34 (i.e. a ‘torsional pre-load force’) may be adjusted by placing the tab 38a in a particular slot 40. The innermost tab 38b is, when assembled, held in place in a slot 42 of the arbor 36. Thus, rotating the arbor 36 relative to the housing 18 varies the torsion of the torsion spring 34, storing energy within the spring 34.

[0099] When the valve 2 is in the closed position, a user must apply a sufficient external torque in order to reset the valve 2 to the open position. In order to achieve this, the user applies a force to the handle 22, which is coupled to the arbor 36, which in turn is coupled to the operating member 10 of the valve 2. As the arbor 36 is rotated relative to the housing 18 in response to an external torque applied to the handle 22, the operating member 10 of the valve 2 rotates from the closed position to the open position as shown in FIG. 7A. Once in the open position, the button inner 25 is free to ‘pop up’ as shown in FIG. 7B, changing the distance between the top surface of the button inner 25 and the button housing 21 from d1 to d2, causing an audible ‘click’ that the user can hear.

[0100] Once the open position is reached, the arbor 36 is held in place by the housing 18. Thus the arbor 36 is ‘latched’ by the housing 18 until the button 20 is pressed.

[0101] As can be seen in FIG. 8, the button 20 has a tapered triggering tab 44 that, when the valve 2 is in the open position, abuts a tapered stop face 46 on the main body assembly. In this example, the tapered stop face 46 is on the lid portion 19. This operation may be understood with further reference to FIGS. 10A-D as outlined in further detail below.

[0102] The tab 44 has a pair of chamfered side surfaces 48 which are each at an oblique angle to the axis about which the valve 2 rotates. The chamfered side surfaces 48 of the tab 44 abut corresponding chamfered side surfaces 50 of the stop face 46 when the arbor 36 is held by the latching mechanism. The tab also comprises a chamfered front surface 52. The chamfered side surfaces 48 of the tab 44 and the chamfered side surfaces 50 of the stop face 46 correspond to one another such that their sloped side surfaces 48, 50 substantially match one another.

[0103] This means a portion of the torque 58 from the torsion spring 34 creates a downward force component on the button 20 to compensate for friction, making depressing the button 20 easier than it would be without the taper. The button 20 is supported by a trigger spring 54. By adjusting the trigger spring force, the force required to depress the button 20 can be adjusted.

[0104] Additionally, the taper can be chosen so that the valve 2 can be closed with the lever arm, without using the button. This will require high torque but may prevent damage to the valve if the handle 22 is forced while ultimately allowing the valve 2 to be closed.

[0105] An overview of operation when the button 20 is pressed can be seen in FIGS. 9A-E, with further reference to FIGS. 10A-D. For reference, a cross-section of the actuation unit 16 is shown in FIG. 11.

[0106] FIG. 9A shows the actuation unit 16 when the valve 2 is in the open position, without the button assembly visible for ease of understanding. In this position, the valve 2 is held in the open position, because the arbor 36 is latched as outlined above. As can be seen in FIG. 10A, in the open position, the rotational force 58 of the torsion spring 34 cannot close the valve because of the latching mechanism, i.e. the tab 44 on the button housing 21 is held in abutment against the stop face 46. The tab 44 is biased upwards by the trigger spring 54.

[0107] The user then presses down the button 20 by applying an ‘axial’ force 56, i.e. along the axis of the operating member 10 of the valve 2, as shown in FIG. 9B, compressing the trigger spring 54. As can be seen in FIG. 10B, this moves the tab 44 downwards relative to the stop face 46. Due to the chamfered side surfaces 48, 50 of the tab 44 and stop face 46, a component 59 of the rotational force 58 provided by the torsion spring assists with the downward motion of the tab 44.

[0108] This allows the tab 44 on the button housing 21 to pass under the stop face 46 of the housing 18, releasing the arbor 36 from the latching mechanism and permitting the torsion spring 34 to impart a rotational force 58 on the arbor 36, as shown in FIG. 9C.

[0109] Once the tab 44 has moved sufficiently downwards relative to the stop face 46 as shown in FIG. 9C, the tab 44 passes under the stop face 46 as shown in FIG. 10C. The rotational force 58 is then free to bias the valve 2 to the closed position, as shown in FIG. 9D.

[0110] Once in the closed position, the trigger spring 54 imparts an upward axial force 60, which pops the button 20 up as shown in FIG. 9E and FIG. 10D, and the tab 44 moves upward relative to the stop face 46, on the other side of the stop face 46 having gone through a rotation of 90°. The button 20 moving upwards may make an audible click which may indicate to the user that the valve is closed. This click may be sufficiently loud that it may be heard over a telephone, e.g. by a telephone operator talking the user through shutting off the gas supply.

[0111] FIG. 12 is a cross-sectional drawing showing a fire protection mechanism within the actuation unit 16. FIGS. 13A-C are schematic drawings illustrating operation of fire protection mechanisms. Specifically, FIGS. 13A and 13B illustrate operation of the protection mechanism of FIG. 12, while FIG. 13C shows an alternative construction.

[0112] In this embodiment, a thermal washer 62 having a selected melting temperature is provided between the button inner 25 and a lip 64 of the button housing 21 on which the button inner 25 rests, as can be seen in FIG. 13A.

[0113] This thermal washer 62 acts as fuse by failing at a specific high temperature, i.e. its melting point, such that it melts. When the thermal washer 62 melts as shown in FIG. 13B, this allows the button 20 to move upwards in response to the force 60 from the trigger spring 54, allowing the button 20 to pass over the button inner 25, forced upwards by the trigger spring 54. Once the button 20 has moved upwards, the arbor 36 is free to rotate and is forced by the torsion spring 34 to close the emergency control valve 2.

[0114] FIG. 13C shows an alternative construction in which like reference numerals appended with a prime symbol (′) denote like components. As can be seen in FIG. 13C, the thermal washer 62′ may be placed at an angle, rather than flat, with a suitable slope of the lip 64′ of the button housing 21′. This sloping of the thermal washer 62′ may advantageously help to prevent the button 20 getting caught in case of less-than-optimal concentricity or uneven loading.

[0115] FIGS. 14A and 14B are schematic diagrams showing an alternative sacrificial triggering mechanism in which like reference numerals appended with a double prime symbol (″) denote like components. In this arrangement, the tab 44″ of the button housing 21″ is held in place by a fixed stop feature 46″, which prevents the rotation of the button housing 21″ and associated arbor (not shown) under the rotational force 58″ of the torsion spring (not shown).

[0116] The stop feature 46″ has a sacrificial part 62″ which melts when exposed to a sufficiently high temperature, such that it no longer holds the tab 44″ of the button housing 21″, thereby allowing rotation of the button housing 21″ and associated arbor (not shown) under the influence of the torsion spring (not shown), i.e. in response to the rotational force 58″.

[0117] FIGS. 15A-C are schematic drawings that show an alternative actuation unit 116 with a side button 120 in accordance with a further embodiment of the present invention. FIGS. 16A-C are further schematic drawings illustrating operation of the actuation unit 116 of FIGS. 15A-C.

[0118] In addition to the top button 120, which operates in the same way as described above, the actuation unit 116 is provided with a pair of side buttons 170a, 170b arranged to trigger release of the arbor 136 in response to a lateral force 176 applied by the user, i.e. in response to one or both of the side buttons 170a, 170b being pushed or squeezed against the restorative force from corresponding side button springs 171a, 171ab.

[0119] In the actuation unit 116, a bypass plate 174 is provided which, if moved, releases the latching mechanism such that the arbor 136 and top button assembly 120 (together with the associated handle 122) to rotate around the axis of the valve, driving the valve to the closed position.

[0120] In FIGS. 15A and 16A, the valve is in the open position, and the bypass plate 174 holds the arbor 136 in place. However, when the user presses either side button 170a, 170b by applying a lateral force 176, this causes the bypass plate to move in a radial direction 178 away from the arbor 136, releasing the tab 144 of the button housing 121.

[0121] This can be seen in FIGS. 15B and 16B, in which the bypass plate 174 moves backwards, allowing the tab 144 on the button housing to pass and thus the arbor 136, button housing 121, and handle 122 to rotate about the axis of the operating member of the valve in a rotational direction 180 about the axis of the valve's operating member.

[0122] Once the valve is in the closed position as shown in FIGS. 15C and 16C, an extruded boss 182 on the arbor 136 prevents the bypass plate 174 from returning to its forward position.

[0123] FIG. 17 is a schematic drawing that shows an actuation unit 216 with a pull-tab trigger mechanism in accordance with a further embodiment of the present invention. FIGS. 18A-D are schematic drawings that show this actuation unit 216 connected to a Bowden cable trigger mechanism.

[0124] Similarly to the actuation unit 116 described previously with reference to FIGS. 15A-C and 16A-C, a bypass plate 274 provides a latching mechanism by which the arbor 236 is held in place. The actuation unit 216 has a top button 220 trigger and handle 222 which operate in the same way described with reference to the actuation unit 16 of FIGS. 3 to 6. Similarly, the actuation unit 216 also has side buttons 270a, 270b that can move the bypass plate 274 backwards in the manner described previous with reference to the actuation unit 116 of FIGS. 15A-C and 16A-C.

[0125] In this arrangement there is a remote terminal 300 with a button 302 and an indicator 304. The button 302 can be used to trigger release of the latching mechanism, thereby closing the valve, as explained below. The indicator 304 provides a visual indication of whether the gas is on or off (i.e. whether the valve is open or closed respectively).

[0126] As can be seen in FIG. 18A, initially the gas is on as indicated by the indicator 304. When a user presses the external button 302 by applying a force 276, the inner core of a Bowden cable 306, attached to the button 302, is pulled, i.e. it applies a lateral force 280 to the bypass plate 274. The other end of the inner core of the Bowden cable 306 is connected to the bypass plate 274, which acts as a pull tab.

[0127] As shown in FIG. 18B, the bypass plate 274 therefore moves backwards, away from the arbor 236, allowing button tab to pass and thus the arbor 236 to rotate in the rotational direction 282, therefore driving the operating member of the valve toward the closed position. During this motion, the arrow on the indicator 304 indicates that the valve is not fully closed.

[0128] As can be seen in FIG. 18C, and similarly to the corresponding feature described with respect to the actuation unit 116 of FIGS. 15A-C and 16A-C, an extruded boss on the arbor 236 prevents the bypass plate 274 from returning to its forward position. The arrow on the indicator 304 indicates that the valve is still not fully closed.

[0129] The extruded boss on the arbor 236 is stepped towards the end of its travel which allows for further movement of the bypass plate 274. This allows more accurate indication at the remote terminal 300 that the valve is fully closed, as shown in FIG. 18D.

[0130] FIGS. 19A and 19B are cross-sectional drawings showing the remote terminal 300 in more detail. Within a housing 308 of the remote terminal 300 is located a pair of rotating arms 310 and a tensioning spring 312 which is arranged to maintain the button position once the bypass plate 274 is in the not return position and to ensure the indicator 304 is correctly registering lever position and valve state. The rotating arms 310 translate a vertical movement of the button 302 to a horizontal movement of the Bowden cable carrier 314. This spring 312 must be lower in force than the side button springs 271a, 271b so that the button remains in the up position when the bypass plate is in the locked position.

[0131] The button 302 only returns to the up position once the valve is turned to the open position, i.e. when the gas is on. In this position, the bypass plate 274 can return under the action of the side button springs to the locked position. The side button springs 271a, 271b push the side buttons 270a, 270b outwards, and pivot around their connection point with the housing of the actuation unit 216. This pushes the bypass plate 274 forwards, back to the locked position.

[0132] FIGS. 20A-C are cross-sectional drawings that show an alternative mechanism that allows for the valve to be closed manually. In this arrangement, the button 420 has a curved triggering tab 444 that, when the valve 2 is in the open position, abuts a curved stop face on the main body assembly (not shown).

[0133] The tab 444 has a pair of curved side surfaces 448 which are each curved with respect to the axis 450 about which the valve rotates, such that the angle θ.sub.1, θ.sub.2 between the normal to the curved surfaces 448 and the axis 450 varies across the curved surfaces 448. The curved side surfaces 448 of the tab 444 abut corresponding curved side surfaces of the stop face when the arbor is held by the latching mechanism. The curved side surfaces 448 of the tab 444 and the curved side surfaces of the stop face correspond to one another such that their sloped side surfaces substantially match one another, mating in a similar way to a coarse screw thread.

[0134] FIGS. 21A-C are schematic drawings of an actuation unit 500 with a sacrificial triggering mechanism that uses a frangible glass bulb 502 in accordance with a further embodiment of the present invention.

[0135] In this particular arrangement, the sacrificial element which provides fire protection is a frangible glass bulb 502 arranged to break when exposed to a fire. When exposed to a temperature exceeding a threshold amount (i.e. a degree of heat associated with the presence of fire), a heat-sensitive fluid (typically a liquid) inside the glass bulb 502 rapidly expands, causing the bulb 502 to shatter. The temperature at which the bulb 502 breaks generally depends on the geometry of the bulb 502 and/or the composition of the fluid within the bulb 502.

[0136] In addition to the latching mechanisms described previously, in this embodiment a pivot arm 504 is positioned between the glass bulb 502 and the arbor (i.e. the driving member) such that it is in contact with both when fully assembled, as shown in FIGS. 22A and 22B. Specifically, when fully assembled, one side of the bulb 502 is held in contact with the pivot arm 504 (i.e. the bulb retainer).

[0137] The opposite side of the bulb 502, which is tapered, is held within a suitably sized milled slot 506 which is located on the lid 508 of the housing 510. Thus the milled slot 506 acts as a ‘socket’ for the bulb 502.

[0138] The pivot arm 504 is mounted to the lid 508 of the housing 510 via a suitable pivot point 512, e.g. a dowel or hinge point, such that the pivot arm 504 may rotate about the pivot point 512. Thus the pivot point 512 provides the axis of rotation for the pivot arm 504.

[0139] The axis of the pivot point 512 is generally normal to the plane of the housing lid 508, and thus parallel to the axis of rotation of the valve.

[0140] FIGS. 22A-B are further schematic drawings illustrating the operation of the sacrificial glass bulb triggering mechanism of FIGS. 21A-C. In particular, FIG. 22A shows the actuation unit 500 under normal operation, when the unit 500 is fully assembled. As can be seen in FIG. 22A, the pivot arm 504 is held in abutment between the glass bulb 502 and the arbor 514.

[0141] This pivot arm 504 is therefore ‘wedged’ between the bulb and the arbor 514 so as to prevent rotation of the arbor 514. Of course, the arbor 514 may still rotate in response to the other methods of releasing the latching mechanism outlined above as appropriate (e.g. in response to a button being pressed, a tab being pulled out, etc.). Thus so long as the glass bulb 502 remains intact (i.e. there has been no fire) the pivot arm 504 resists the rotational spring force being applied to the arbor 514 by the internal spring, where this rotational force has been discussed previously.

[0142] As can be seen in FIG. 22B, when exposed to sufficient heat (e.g. during a fire), the glass bulb breaks. As a result, the pivot arm 504 is then free to rotate and occupy space previously occupied by the glass bulb 502. With the resistance from the glass bulb 502 removed, the arbor 514 pushes the pivot arm 504 out of the way (i.e. it ‘swings around’ the pivot point 512) under the force from the spring within the actuation unit 500.

[0143] This results in the valve to which the actuation unit 500 is connected—which is mechanically coupled to the arbor 514—to rotate in the manner described previously, thereby biasing the valve to the closed position. This may be particularly advantageous, for example, for shutting off the domestic gas supply during a fire, thereby limiting the risk of flammable gas from coming into contact with the flames.

[0144] Thus it will be appreciated that embodiments of the present invention provide an improved valve assembly in which the valve is retained in the open position until a triggering force is applied by a user, and which locks or latches only when the valve is in the open position such that it cannot be held at an intermediate position, improving safety for domestic gas supplies. Once triggered, the ‘spring-loaded’ actuation unit biases the valve to the closed position automatically, i.e. the user does not need to apply any torque to close off the valve. While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that the embodiments described in detail are not limiting on the scope of the invention as defined by the accompanying claims.