GB2171176A

GB2171176A - Slam-shut valves

Info

Publication number: GB2171176A
Application number: GB08503788A
Authority: GB
Inventors: Kenneth M Cooper; Alan F Redpath; Stanley V Devey; Robert R Johnson
Original assignee: Bryan Donkin Co Ltd
Current assignee: Bryan Donkin Co Ltd
Priority date: 1985-02-14
Filing date: 1985-02-14
Publication date: 1986-08-20
Also published as: GB2203523B; GB8503788D0; GB2171176B; GB8811488D0; GB2203523A

Abstract

A slam-shut valve has a valve member 21 pivotal between an open position and a closed position, the valve member being accommodated in a valve chamber 14 forming part of a flow passage and the valve member being caused to move into the closed position as a result of a prevailing unwanted overpressure condition which operates on a diaphragm 33. A manual reset mechanism is operable from the exterior of the slam-shut valve to move the valve member to open position. The reset mechanism comprises a rotatable shaft 66 carrying a pick-up pin 70 or finger engageable with a spindle 65 on valve lever 20 to move it from closed to open position. Before resetting a bleed passage communicates the valve chamber with the flow passage at the other side of the valve member by means of a manually-operable, normally-closed bypass valve which is accessible from the exterior of the slam-shut valve to permit opening thereof to achieve pressure equalisation. <IMAGE>

Description

SPECIFICATION Slam-shut valves This invention relates to slam-shut valves.

Generally such a valve is employed in combination with a pressure regulator to provide overpressure protection for a pressure fluid-handling apparatus generally disposed in or consisting of a pipeline, the regulator, in terms of fluid flow, being upstream of the apparatus with the slam-shut valve being, in turn, upstream of the regulator. If the latter fails or the apparatus is subjected to excessive pressure, for whatever reason, the sla m-shut valve is automatically triggered to close (its normal condition being open) thus preventing further flow of fluid, generally gas.

Such slam-shut valves usually have a manual reset mechanism whereby the valve can be reset to open once the cause of regulator failure or overpressure has been rectified.

An example of a slam-shut valve with a reset assembly is disclosed in British Patent Specification No. 1 561 246. The reset mechanism disclosed in this patent specification requires a two step re-setting operation in that a reset shaft requires firstly to be pushed inwardly to connect with a latching lever and secondly to be rotated to move the now captive latching lever to a valve latched open position.

Additionally the valve door of the slam-shut valve disclosed in said patent specification mounts a pressure-equaliser valve which serves the function of equalising fluid (gas) pressure on opposite sides of the closed valve door once the over-pressure condition has been corrected which is necessary before the valve door can be manually reset to open.

The incorporation of the pressure-equaliser valve in the valve door is not considered to be wholly desirable and tends to over-complicate the valve door construction.

It is one of the objects of the present invention to provide an alternative simpler reset assembly for a slam-shut valve.

According to the present invention there is provided a slam-shut valve comprising a body defining a flow passage including a valve chamber within which is disposed a slam-shut valve member connected to a lever fast with a pivot spindle and normally maintained in a valve-open position by a pivoted latch engaging the lever and operatively connected to a release shaft extending into a diaphragm chamber mounted on the valve body and being operatively connected to a spring-loaded diaphragm therein via a release connection, the diaphragm being adapted to sense an over-pressure in the diaphragm chamber and to move to break the release connection to effect movement of the release shaft to disconnect the latch from the slam-shut valve member and permit the latter to pivot to a valve-close position, and a manually-operable reset mechanism being provided to pivot the slam-shut valve member from the valve-close position to the latched valve-open position, after pressure equalisation or near pressure equalisation on both sides of the closed valve member is achieved, the reset mechanism comprising a pick-up spindle carried by the lever and parallel with the pivot spindle and a rotatable reset shaft disposed laterally of the pick-up spindle and having a pick-up pin normal thereto for engaging the pick-up spindle, upon rotation of the reset shaft to pivot the pick-up spindle, lever and slam-shut valve member upwardly until latching engagement between the lever and latch is achieved to return the valve to open position.

It is another object of the present invention to provide a slam-shut valve with a pressure equalisation arrangement separate from the valve member and readily accessible for external operation.

Also according to the present invention therefore there is provided a slam-shut valve comprising a valve body defining a flow passage including a valve chamber within which is disposed a slam-shut valve member adapted to move from a valve-open position to a valve-closed position upon occurrence of an overpressure in a pipeline and/or fluid handling system with which the slam-shut valve is associated, and a pressure-equalisation arrangement for use when the overpressure condition is corrected and comprising a pressure bleed passage joining the valve chamber and the flow path at the other side of the closed valve member, and a pressure-equalising bypass valve, normally resiliently closed, disposed in said passage at the valve chamber end and comprising a manually operable shaft accessible from the valve when pressure equalisation is required, and mechanical means for releasably retaining the bypass valve in open position.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a side elevation of a slam-shut valve according to the invention; Figure 2 is a transverse sectional view with the valve door in closed position; Figure 3 is a sectional detail view of the bypass valve; and Figure 4 is a fragmentary sectional view of the slam-shut valve showing an alternative diaphragm spring loading arrangement suitable for when the slam-shut valve is to be used at pressures higher than those normally encountered by the slam-shut valve arrangement of Figure 1 to 3.

The slam-shut valve 10 comprises a body 11 defining a gas flow passage 12 and has at each end of the body 11 a mounting or assembly flange 13 whereby the valve 10 can be mounted in a pipeline (not shown).

The flow passage 12 has intermediate its end a valve chamber 14 at the outlet side of which is a valve seat 15 mounted in the valve body 11 coaxial with the flow passage 12.

The valve chamber 14 is open at one side, generally its top, and this open side is closed by a lid or cover structure 16, a sealing element 17 being located between the valve body 11 and the valve cover structure 16.

Extending inwardly ofthevalve chamber 14from the cover structure 16 is a pair of side-by-side arms 18 between which is pivoted at spindle 19 a lever 20.

The latter mounts a valve door 21 provided with an annular seating face 22 for engaging the valve seat 15 when the valve door 21 is in closed position.

The valve door 21 is connected to the lever 20 by a spindle 23 passing through the door 21, the other face of the door 21 being correspondingly recessed to accommodate an O-ring 25 held therein by a washer or flange 26 on the spindle 23. A second O-ring 27 is sandwiched between the washer or flange 26 and the lever 20.

This mounting arrangement of the valve door 21 on the lever 20 permits limited relative movement between the lever 20 and the valve door 21 (i.e. a floating mounting) to ensure that the latter always correctly and sealingly engages the valve seat 15. It will also be manifest that the O-rings 25,27 provide effective sealing for the mounting arrangement.

The lever 20 at its pivot end is provided with a cam formation 28 whereof its function is to provide a visual indication of whether the valve door 21 is open or closed.

As can be seen from Figure 1, the valve door 21 is movable from an upper horizontal, valve-open position down through typically a 90" arc to a vertical valve-closed position.

The valve cover structure 16 above the cam formation 28 has an outwardly (generally upwardly) extending tubular housing 29 closed at its outer (upper) end and transparent at least insofar as its length external of the cover structure 16 is concerned.

Slidable within the housing 29 is an indicator rod 30 which is resiliently constrained by a spring arrrangement 31 into contact with the cam formation 28.

When the valve door 21 is open the indicator rod 30 does not extend into the external length of the housing 29. When the valve door 21 is moved to the valve-closed position, the cam formation 28 pushes the indicator rod 30 up into the external length of the housing 29 thus indiating a valve-closed condition to an observer.

It will be manifest that when the valve door 21 is again in valve-open position the indicator rod 30 will be resiliently withdrawn down into the housing 29.

An alternative arrangement would be to shroud the top part of the external length of the housing 29 and for the indicator rod 30 always to be visible, the indicator rod 30 having two adjacent coloured portions, say green and red with the green upper.

Thus when an observer sees the green portion of the indicator rod 30 he knows the valve door 21 is in open position. When the valve door 21 moves downwardly to the closed position the green portion moves into the shroud and the red portion becomes visible thus telling an observer that the valve door 21 is closed.

The valve cover structure 16 is itself open at one side (generally its top) and is closed by a spring housing 32, there being a diaphragm 33 clamped between the cover structure 16 and the spring housing 32.

The diaphragm 33 is resiliently loaded by a spring 34 contained within the spring housing 32 and extending between the diaphragm 33 and a spring pressure adjustor 35. Thus the spring pressure loading on the diaphragm 33 can be predetermined to suit required operational conditions.

A retaining cup 36 is fastened centrally to the diaphragm 33 and extends into the cover structure recess 37.

This cup 36, in turn, extends freely into a recess 38 in a housing 39 secured to the cover structure 16.

Within the cup 36 is a movable release shaft 40 which extends through the housing 39 and projects into the valve chamber 14.

This shaft 40 has a tubular sleeve 41 fixed thereto which normally rests on balls 42 when the retaining cup 36 is fully within the recess 38.

The boss 39 is also recessed as indicated at 43 to accommodate a spring 44 located between an O-ring retainer 45 mounted in the boss 39 and one limb 46 of a bellcrank lever 47. The O-ring retainer 45 serves to secure a sealing O-ring 45A between the shaft 40 and the housing 39. The bellcrank lever 47 is pivoted at 48 to a lug 49 on the cover structure 16 and has on its other limb 50 a projection or lip 51 for engaging the lever 20 to hold the valve door 21 in the upper open position.

The lipped bellcrank lever 47 thus constitutes a latch.

The limb 46 mounts a tubular spring locator 52 engaging on a bearing ring 53 which, in turn, engages a spherical terminal member 54 on the end of the shaft 40.

A pressure inlet port 55 is provided in the cover structure 16 and is connected by piping to one or more locations where gas pressure is to be sensed, for example downstream of the pressure regulator (not shown).

If the latter allows, for example, a downstream overpressure, i.e. a pressure above the set spring pressure, then the diaphragm 33 is caused to flex so as to lift the retaining cup 36 outwardly of the recess 38 thus allowing the balls 42 to roll away from the shaft 40, i.e. out from under the sleeve 41 The shaft 40 consequently drops and the spring 44 urges the limb 46 of the latch 47 downwards. The lip 51 of the latch 47, as a result, is pivoted clear of the lever 20 and the valve door 21 slams shut against the valve seat 15 where it is retained by the gas overpressure present in the flow passage 12 and consequently the valve chamber 14 and also by a torsion spring 72 carried on the spindle 19 and which acts between the cover structure 16 and a spindle 65 of a reset mechanism to be described later, the spindle 65 being carried by the lever 20.

Before the valve door 21 can be reset to open position it is necessary to equalise or nearly equalise the gas pressure on opposite sides of the valve door 21.

Between the valve chamber 14 and the outlet side of the flow passage 12 is a bleed passage 73 which is closed by a bypass valve 56 located in the valve body 11 at the valve chamber end of the passage 55. The bypass valve 55 comprises a shaft 57 slidable and rotatable through 360" within a guide bush 58 in the valve body 11. The guide bush 58 has a transverse passage 59 open to an annular recess 60 in the bush 58.

The bypass valve 56 is normally closed and a spring 74 acts between a shoulder of the bush 58 and a flange 61 on the shaft 57 to constrain the bypass valve 56to its closed position.

The bypass valve 56 has a cross pin 62 at its inner end, i.e. its end within the valve chamber 14 and this cross pin 62 can be moved over a cam formation 63, for example of castellated formation, between a low position as shown in Figure 3 (bypass valve closed) and a high position (bypass valve open). In the latter condition, gas flows from the valve chamber 14 down the sides of the valve shaft 57, along passage 59, into annular recess 60 and then into the bleed passage 73 to the other side of the closed valve door 21 until pressure equalisation (or near equalisation) on opposite sides of the latter is achieved.

When the valve door 21 is opened the bypass valve 56 is normally closed. On occurrence of an overpressure the valve door 21 slams shut as aforesaid. Once the problem concerning the overpressure has been resolved, an operator unscrews an environmental protective cover 64 protecting the end of the shaft 57 and moves the latter inwardly and angularly to the high position on the cam formation 63 where it is held by the cross pin 62 until pressure equalisation is obtained on opposite sides of the valve door 21, the bypass valve 56 now being open.

The latter is then re-set to its open position as will shortly be described, the aforesaid spindle 65 as a result of the upward arcing movement of the lever 20 and the valve door 21 striking the cross pin 62 and causing it to rotate to the low position on the cam formation 63. Spring 74 consequently urges the shaft 57 outwardly thus closing the bypass valve 56.

O-rings 57A, 57B and 58A are provided respectively between the head of the bypass valve 56 and the bush 58, the shaft 57 and the bush 58 and the bush 58 and the valve body 11 for sealing purposes.

In the event that the bypass valve 56 is open when the valve door 21 slams shut it will be manifest that the aforesaid spindle 65 strikes the cross pin 62 lying at the high point of cam formation 63 and knocks it to the low position thus closing the bypass valve 56 (i.e.

fail safe operation) until the overpressure condition is corrected whereupon the aforesaid pressure equalisation operation is effected.

It will be manifest that the bypass valve 56 can be closed simply by manually rotating the shaft 57 and allowing the force of the spring 74 to axially move the shaft 57 and consequently the valve to closed position.

In a modification, the cross pin 62 and cam formation 63 are omitted, the bypass valve 56 simply bein opened by manually pushing on the shaft 57 and holding the valve open until pressure equalisation or nearly so is achieved. The shaft 57 is then simply released and the spring 74 returns the valve to closed position.

The cross pin 62 may be replaced by a curved or arcuate camming formation.

A manual reset mechanism, according to the present invention, is provided to return the valve door 21 from the closed position to the open position. This mechanism includes the laterallyextending spindle 65 on the lever 20. It also includes an operating shaft 66 extending through a bush or bearing 67 in the valve body 11, the shaft 66 terminating outside the valve body 11 in a square (or other non-circular) formation 68 for engagement by typically a wrench, key or spanner. The formation 68 is enclosed in a removable environmental cover 69.

The inner end of the shaft 66 mounts a pick-up pin or finger 70 normally lying in a plane parallel with the plane containing the valve door 21 when the latter is shut.

A torsion spring 71 loads the shaft 66 to maintain the pick-up finger 70 in such position.

Here it should be noted that the torsion spring 72 loads the spindle 65, as aforesaid, to urge it to rotate the lever 20 and consequently the valve door 21 downwards to closed position.

If the valve door 21 is closed and pressure equalisation has been attained or nearly so then the valve door 21 is reset by an operator removing the cover 69, engaging the formation 68 with typically a spanner, key or wrench and rotating the shaft 66 to cause the finger 70 to pick-up the spindle 65 and lift the valve door 21 upwardly until the lever 20 contacts the spherical terminal member 54 on the shaft 40 and raises same to permit the balls 42 to oonce again take up the position shown in Figure 1, lowering of the diaphragm 33 causing the retaining cup 36 to enclose the balls 42, and the bellcrank lever 47 to pivot to latch the lever 20 and consequently the door 21 in open position.

When the valve door 21 is once again latched the torsion spring 71 rotates the shaft 66 back to the position where the pick-up finger 70 is downwardly vertically disposed.

The environmental cover 69 is replaced and the slam-shut valve is once again in its operational open position.

Reference is now made to Figure 4 which shows an alternative diaphragm spring-loading arrangement suitable for when the slam-shut valve is to operate at pressures higher than those normally encountered by the slam-shut valve of Figures 1 to 3.

Such higher pressures lie, for example, within the range 0.35 bar to 4 bar.

In this arrangement like parts to those in Figures 1 to 3 are designated by the same references with the suffix "A" appended.

In this arrangement, the spring housing 32A, like the spring housing 32 of Figures. 1 to 3, houses a diaphragm loading spring 34A.

A spring pressure adjusting mechanism is generally indicated at 80, which mechanism has an adjustment spindle 81 projecting outside the spring housing 32A and which is operable typically by a wrench, key or spanner. Normally, it is enclosed by an environmental cover 82.

As this slam-shut valve operates at higher pressures it is important to ensure that the retaining cup 36A, on re-latching the valve door in open position, is not seated in the recess 38A of the housing 39A in the position shown in Figure 4 by the spring 34A with a force sufficient to damage or even destroy same.

For this reason, a lost-motion connection is provided between the spring 34A and the retaining cup 36A.

More specifically, the retaining cup 36A is provided with an upwardly-extending projection 83 formed with a vertically-elongate slot 84. This projection 83 extends into a slot 85 in a piston member 86 which carries a cross pin 87 bridging the slot 85 and extending through the slot 84 in the projection 83. This piston member 86 is bolted as indicated at 88 to an upper piston member 89, the diaphragm 33Abeing clamped between the piston members 86 and 89.

The diaphragm loading spring 34A is seated between the pressure adjusting mechanism 80 and a cup-shaped configuration 89A of the piston member 89.

The piston member 86, when the valve door is in latched-open position, rests on an internal ledge 90 of the cover structure 1 6A and the cross pin 87 is spaced a few millimetres down from the closed upper end of the elongate slot 84.

The cover structure 16A is formed with circumferentially spaced recesses 91 in the region of abutment between the cover structure 1 6A and the piston member 86 to provide gas flow passages from below the latter to the lower side of the diaphragm 33A.

An internal shoulder 92 is formed in the spring housing 32A above the piston member 89 and is adapted to be butted by the latter when the valve door slams shut. The purpose of this shoulder 92 is to act as a stop to prevent excessive movement of the retaining cup 36A relative to the housing 39A, i.e.

to prevent the retaining cup 36Afrom egressing from the housing 39A.

A spring 93 is connected between the piston member 86 and the retaining cup 36A and serves to urge the latter into the housing 39A.

In use, when there is an excess pressure in the valve cover structure 16A acting on the diaphragm 33A (i.e. overcoming the force of the spring 34A and causing unlatching of the valve door) the diaphragm/ piston assembly 33A, 86,89 moves upwardly. This causes the cross-pin 87 to pick up on the projection 83 and raise the retaining cup 36A relative to the housing 39A with the consequent results as previously described with reference to Figures 1 to 3. As aforesaid, abutment of piston member 89 on the shoulder 92 prevents the retaining cup 36A egressing from the recess 38A of the housing 39A.

When, the gas pressure sensed by the diaphragm 33A is reduced, the spring 34A urges the diaphragm/ piston assembly 33A, 86,89 downwardly until the piston member 86 abuts the ledge 90. Due to the lost motion connection (elongate slot 84 and cross pin 87) between the diaphragm/piston assembly 33A, 86,89 the force of the spring 34A is not applied to the retaining cup 36A, nor the balls 42A or the housing 39A. When the release connection 36A, 42A, 39A is reset as previously described by moving the valve door and the lever to the fully open position, the lighter rate spring 93 causes the retaining cup 36Ato be fully seated in the recess 38A of the housing 39A thereby returning the balls 42A under the sleeve 41A in the reset condition.

Thus with this high pressure slam-shut valve damage to the retaining cup 36A is obviated or mitigated.

Claims

1. A slam-shut valve comprising a body defining a flow passage including a valve chamber within which is disposed a slam-shut valve member connected to a lever fast with a pivot spindle and normally maintained in a valve-open position by a pivoted latch engaging the lever and operatively connected to a release shaft extending into a diaphragm chamber mounted on the valve body and being operatively connected to a spring-loaded diaphragm therein via a release connection, the diaphragm being adapted to sense an over-pressure in the diaphragm chamber and to move to breakthe release connection to effect movement of the release shaft to disconnect the latch from the slam-shut valve member and permit the latter to pivot to a valve-close position, and a manually-operable reset mechanism being provided to pivot the slam-shut valve member from the valve-close position to the latched valve-open position, after pressure equalisation or near pressure equalisation on both sides of the closed valve member is achieved, the reset mechanism comprising a pick-up spindle carried by the lever and parallel with the pivot spindle and a rotatable reset shaft disposed laterally of the pick-up spindle and having a pick-up pin normal thereto for engaging the pick-up spindle, upon rotation of the reset shaft to pivot the pick-up spindle, lever and slam-shut valve member upwardly until latching engagement between the lever and latch is achieved to return the valve to open position.

2. A slam-shut valve as claimed in claim 1, in which the lever is spring-loaded to urge the slamshut valve member down into the valve-closed position.

3. A slam-shut valve as claimed in claim 1 or 2, in which the reset shaft is spring-urged to a position where the pick-up pin is clear of the pick up spindle.

4. A slam-shut valve as claimed in any one of claims 1 to 3 in which the lever, at the region where it is fast with the pivot spindle has a cam surface adapted to act upon a spring-loaded verticallymovable indicator element housed in a bore in the valve body and extending into a transparent cover above and outside the valve body whereby, depending upon whether the slam-shut valve member is closed or open, the indicator element is either visible or not, or visibly indicates the position of the valve member.

5. A slam-shut valve as claimed in any one of claims 1 to 4 in which the latch is an angled lever pivoted at its apex to a cover of the valve body with one end engageable under the lever and the other end spring-loaded to pivot said one end clear of the lever upon operation of the release connection.

6. A slam-shut valve as claimed in claim 5, in which the release shaft is held in a valve-open position by the release connection which is constituted by ouwardly-movable ball elements maintained under a sleeve on the release shaft by a retaining cup secured to the diaphragm, which ball elements are freed from the cup when the dia phragm reacts to an over-pressure thus permitting the release shaft to fall.

7. A slam-shut valve as claimed in any one of the preceding claims, in which reset shaft has externally of the valve body a formation engageable by a tool to rotate the reset shaft manually to reset the valve to open position.

8. A slam-shut valve as claimed in claim 7 in which a removable environmental cover protects the formation engageable by the tool.

9. A slam-shut valve as claimed in any one of claims 1 to 8 in which a pressure bleed passage joins the valve chamber and the flow passage at the other side of the closed valve member, a pressureequalising bypass valve, normally closed, being disposed in said passage at the valve chamber end, the bypass valve comprising a manually-operable shaft for opening the bypass valve when pressure equalisation is required and accessible from the valve body exterior.

10. A slam-shut valve as claimed in claim 9 in which the bypass valve shaft is spring urged to close the bypass valve.

11. A slam-shut valve as claimed in claim 9 or 10 in which the bypass valve includes mechanical means for releasably retaining the bypass valve in open position.

12. A slam-shut valve as claimed in claim 11, in which the mechanical means is a cross-pin connected to and transverse of the bypass valve shaft and which cooperates with a cam formation having a high point (bypass valve open) and a low point (bypass valve closed).

13. A slam-shut valve as claimed in claim 2 in which the cross-pin, when disposed at the cam formation high point, lies in the path of a spindle carried by the pivoting lever, which spindle is adapted to knock the cross-pin to the cam formation low point on contacting same irrespective of the direction of pivoting of the lever.

14. A slam-shut valve as claimed in any one of claims 9 to 13 in which the bypass valve shaft is protected externally of the valve body by an environmental cover.

15. A slam-shut valve as claimed in any one of claims 5to 14 in which there is a lost-motion connection between the spring-loaded diaphragm and the release connection to ensure that the latter is not subjected to excessive spring force.

16. A slam-shut valve as claimed in claim 15 in which the release connection incorporates a supplementary spring for loading the release connection to latching condition.

17. A slam-shut valve as claimed in claim 15 or 16 in which the diaphragm is secured to a piston assembly adapted to cooperate with an upper stop to prevent separation of the release connection, and with a lower stop to prevent excess spring force acting on the release connection and to allow operation of the lost-motion connection.

18. A slam-shut valve comprising a valve body defining a flow passage including a valve chamber within which is disposed a slam-shut valve member adapted to move from a valve-open position to a valve-closed position upon occurrence of an overpressure in a pipeline and/or fluid handling system with which the slam-shut valve is associated, and a pressure-equalisation arrangement for use when the overpressure condition is corrected and comprising a pressure bleed passage joining the valve chamber and the flow path at the other side of the closed valve member, and a pressure-equalising bypass valve, normally resiliently closed, disposed in said passage at the valve chamber end and comprising a manually operable shaft accessible from the valve body exterior for opening the bypass valve when pressure equalisation is required, and mechanical means for releasably retaining the bypass valve in open position.

19. A slam-shut valve as claimed in claim 18 in which the bypass valve shaft is spring urged to close the bypass valve.

20. A slam-shut valve as claimed in claim 18 or 19, in which the mechanical means is a cross-pin connected to and transverse of the bypass valve shaft and which cooperates with a cam formation having a high point (bypass valve open) and a low point (bypass valve closed).

21. A slam-shut valve as claimed in claim 20 in which the cross-pin, when disposed at the cam formation high point, lies in the path of a spindle carried by the pivoting lever which is adapted to knock the cross-pin to the cam formation low point on contacting same irrespective of the direction of pivoting of the lever.

22. A slam-shut valve as claimed in any one of claims 18 to 21 in which the bypass valve shaft is protected externally of the valve body by an environmental cover.

23. A slam-shut valve as claimed in any one of claims 18 to 22 in which the valve member is connected to a lever fast with a pivot spindle and normally maintained in the valve-open position by a pivoted latch engaging the lever and operatively connected to a release shaft extending into a diaphragm chamber mounted on the valve body and being operatively connected to a spring-loaded diaphragm therein via a release connection, the diaphragm being adapted to sense an over-pressure in the diaphragm chamber and to move to break the release connection to effect movement of the release shaft to disconnect the latch from the slam-shut valve member and permit the latter to pivot to the valve-close position, and a manually-operable reset mechanism being provided to pivot the slam-shut valve member from the valve-close position to the latched valve-open position, after pressure equalisation or near pressure equalisation on both sides of the closed valve member is achieved, the reset mechanism comprising a pick-up spindle carried by the lever and parallel with the pivot spindle and a rotatable reset shaft disposed laterally of the pick-up spindle and having a pick-up pin normal thereto for engaging the pick-up spindle, upon rotation of the reset shaft to pivot the pick-up spindle, lever and slam-shut valve member upwardly until latching engagement between the lever and latch is achieved to return the valve to open position.

24. A slam-shut valve as claimed in claim 23, in which the lever is spring-loaded to urge the slam shut valve member down into the valve-closed position.

25. A slam-shut valve as claimed in claim 23 or 24, in which the reset shaft is spring-urged to a position where the pick-up pin is clear of the pick up spindle.

26. A slam-shut valve as claimed in any one of claims 21 to 23 in which the lever, at the region where it is fast with the pivot spindle has a cam surface adapted to act upon a spring loaded verticaliy-movable indicator element housed in a bore in the valve body and extending into a transparent cover above and outside the valve body whereby, depending upon whether the slam-shut valve member is closed or open, the indicator element is either visible or not, or visibly indicates the position of the valve member.

27. A slam-shut valve as claimed in any one of claims 23 to 26 in which the latch is an angled lever pivoted at its apex to a cover of the valve body with one end engageable under the lever and the other end spring-loaded to pivot said one end clear of the lever upon operation of the release connection.

28. A slam-shut valve as claimed in claim 27, in which the release shaft is held in a valve-open position by the release connection which is constituted by outwardly-movable ball elements maintained under a sleeve on the release shaft by a retaining cup secured to the diaphragm, which ball elements are freed from the cup when the diaphragm reacts to an over-pressure thus permitting the release shaft to fall.

29. A slam-shut valve as claimed in claims 23 to 28, in which reset shaft has externally of the valve body a formation engageable by a tool to rotate the reset shaft manually to reset the valve to open position.

30. A slam-shut valve as claimed in claim 29 in which a removable environmental cover protects the formation engageable by the tool.

31. A slam-shut valve, substantially as hereinbefore described with reference to the accompanying drawings.