GB2204661A - Gas pressure cut-off device - Google Patents

Abstract

A gas pressure cut-off device comprises an actuator 26 operable to control gas flow past the device; a movable detent, preferably formed by two rollers 42, engageable with the actuator to prevent operation thereof; and means movable under the influence of gas pressure within the device to free the detent and thereby permit operation of the actuator. The means may comprise a member 18 connected to a diaphragm arrangement 12 and having a surface 50, 52 which is engageable with the movable detent. The surface 50, 52 is profiled in such a manner that on movement of the diaphragm arrangement the profiled surface moves in relation to the detent to a point where the detent can itself move to free the actuator which as shown is connected to a closure member 28. In a modification (Fig. 3) the detent is freed by either overpressure or underpressure. <IMAGE>

Description

A GAS PRESSURE CUT-OFF DEVICE The present invention relates to a gas pressure cut-off device and particularly to such a device for connection to a governing service regulator.

Gas pressure cut-off devices are designed to operate at an equilibrium position over a clearly defined range of gas pressures and to react quickly to cut off the gas supply if the gas pressure either increases or decreases past a predetermined upper or lower limit. A device of this type is usually designed to operate either as an over pressure device or as an under pressure device but a single device can be adapted to operate under both conditions. The present invention relates to all these types of devices.

The object of the present invention is to provide a gas pressure cut-off device that is constructed in a simpler fashion that devices known hitherto, which typically include a ball cage arrangement. The use of ball cage arrangements, apart from the complexity of their construction, causes problems when the device is serviced as during this operation the ball cage tends to disarrange itself and require reassembly before the device can be returned to service. A cut-off device according to the present invention does away with the need to include a ball cage and is of a simple construction which especially facilitates servicing.

According to the present invention there is provided a gas pressure cut-off device comprising an actuator operable to effect gas flow past the device, a movable detent engagable with the actuator to prevent operation thereof and means movable under the influence of gas pressure within the device to free the detent and thereby permit operation of the actuator.

Preferably, the means movable under the influence of gas pressure within the device comprises a diaphragm arrangement.

preferably also. the said means comprises a member conected to the @aparagm arrangement and with a surface, which is engagable with the movable detent and profiled in such a manner that on movement of the diaphragm arrangement the profiled surface moves in relation to the detent to a point where the detent can itself move in relation to, and thereby free, the actuator for operation.

Preferably also, the movable detent comprises a roller engagable with an enlarged portion of the actuator to prevent operation thereof.

Preferably also, the actuator comprises a spindle attached to a loaded valve member.

The present invention will now be described by way of example with reference to the accompanying drawing in which: Fig. 1 is a cross-sectional view of a gas pressure cut-off device; Fig. 2 is a partially cut-away perspective view of part of the device shown in Fig. 1; and Fig. 3 is a scrap view showing an alternative arrangement of part of the device shown in Figs 1 and 2.

The gas pressure cut-off device is designed to be attached to a regulator or a gas supply pipe (not shown) and act to cut off the gas supply in the event of the gas pressure rising above a predetermined maximum pressure. The alternative arrangement shown in Fig. 2 is also adapted to act to cut off the gas supply if the gas pressure falls below a predetermined minimum.

As shown in Figs. 1 and 2, the cut-off device comprises a two part casing 10 between the two parts of which is clamped a diaphragm 12. The diaphragm 12 effectively divides the device into two chamber 14 and 15, the first chamber 14 comprising a "pressurised" chamber 14 which communicates via an opening 16 in the casing 10 with the interior of the gas supply pipe, and the second chamber 15 comprising an "atmospheric" chamber which is kept substantially at atmospheric pressure. Clamped to the diaphragm 12 is a profiled member 18, as will be more fully described below, via a support plate 20 located on the "atmospheric11 pressure side of the diaphragm 12.

The diaphragm 12 is spring loaded as at 21 against the gas pressure within the chamber 14, the spring 21 bearing at one end against a fixing boss 22 clamping the member 18 to the plate 20 and at its other end against an adjuster 23 screwed into a cylindrical portion of the casing 10 defining the chamber 15.

The position of the boss 23 along the screw-threaded portion of the casing 10 determines the loading of the spring 21 on the diaphragm 12 and thereby determines the range of working pressures of the device. At the lower end of the range of working gas pressures within the chamber 14, the diaphragm 12 and profiled member 18 are prevented from travel under the influence of the spring loading 21 by an internal ledge 24 formed within the interior of the chamber 14 of the casing 10, connected to the ledge 24 is an annular cage arrangement 25, as will be described through which the member 18 can travel to a limited extent.

Passing through the profiled member 18 is a spindle 26 that forms part of an actuator which is operable to affect the gas flow in the gas supply pipe. The spindle 26 passes out of the casing 10 via an aperture 27 and, in this example, is attached to a valve member 28 which is located in the regulator or the gas supply pipe and designed to locate against a valve seat (not shown) to cut off the SllD21y of cas r"lig the SFJ spindie fB slide through the aperture 27 with respect to the profiled member 18 in order to close the valve member 28 against the valve seat.Gas is prevented from seeping along the spindle 26 by an spring 30 located in the casing 10 around the aperture 26 and by an O-ring 32 located in a groove 34 formed in the member 18.

Actuation of the valve member 28 is additionally accomplished by a spring loading 36, which acts at one end against a flange 38 forming part of the valve member 28 and at its opposite end against a plate 40 inset into the casing 10 around the rim of the aperture 27. The spring loading 36 is normally prevented from actuating the valve member 28 by means of a movable detent formed by two rollers 42. The rollers 42 are retained within the cage 25 and engage a shoulder '44 formed by an increase in diameter of the spindle 26 within the pressurised chamber 14 of the device. The rollers 42 are held in position against the shoulder 44 under normal operating conditions of the device by two plates 46 forming part of the cage 25 and by two prongs or projections 48 forming part of the profiled member 18 as will now be described.

The profiled member 18 is provided with the two projections 48 on opposite sides of the spindle 26 and defining two interior surfaces 50 spaced from but parallel with the adjacent surface of the spindle 26. It is against these surfaces 50 that the rollers 42 normally abut. At the ends of the projections 48, the surfaces 50 flare outwardly of the spindle 26 as at 52 so that the gaps defined between the surfaces 52 and the adjacent surface of the spindle 26 increase until each gap is greater than the diameter of its associated roller 42 and the width of the shoulder 44.Normally, therefore, when the gas pressure within chamber 14 of the device is at the lower end of the device's working range of gas pressures, the rollers 42 are trapped as shown in Figs. 1 and 2 by the plates 46, between which the projections 48 pass, by the shoulder 44 and by the surfaces 50 of the profiled member 18.

In operation, under normal conditions, the cut-off device is maintained in a position as shown in Fig. 1. If the gas pressure within the gas supply pipe and therefore the chamber 14 of the device increases slightly then the diaphragm 12 moves to compensate against the spring loading 21. However, the rollers 42 will still prevent movement of the spindle 26 under the influence of the spring loading 36 whilst they are still trapped against the surfaces 50 of the projections 48. If the gas pressure continues to increase, a predetermined point is reached when the movement of the profiled member 18 and therefore the surfaces 50 and 52 thereof with respect to the spindle 24 is such that the rollers 42 can be moved outwardly into the increased gap formed by the flared out surfaces 54 of the projections 48.

Ultimately, the 'rollers 48 can be moved sufficiently by the action of the shoulder 44 on the spindle 42 under the influence of the spring loading 36 so they no longer impede movement of the spindle 42. The spring loading 36 can, therefore, act to move the valve member 28 against the valve seat to cut off the flow of gas in the pipe.

Fig. 3 shows an alternative arrargement of the profiled member 18 which is designed for use with a gas pressure regulator designed to operate under a fall in gas pressure below a predetermined limit as well as with gas pressure increase.

projections 48 Of th, potq membe 18 are cut away as at 54 so that the gaps defined between their interior surfaces and the adjacent surface of the spindle 26 increase both outwardly of the projections 48 as before but aso inwardly until each gap is greater than the diameter of its associated roller 42 and the width of the shoulder 44. In addition, the spring loading 21 is arranged so that the profiled member 18 is given freedom of movement in the opposite direction to that described above until the predetermined lower pressure limit for operation of the regulator has been reached.

In use of this arrangement, if the gas pressure within the gas supply pipe and therefore the chamber 14 falls, the diaphragm 12 and the profiled member 18 move under the influence of the spring loading 21 so as to increase the size of the atmospheric chamber 15 of the regulator and to decrease the size of the pressurised chamber 14. This movement of the profiled member 18 relative to the spindle 26 permits the rollers 42 to move outwardly of the spindle 26 into the cut away section 54 of the projections 48 so that the spindle 26 is no longer retained by the rollers 42 acting against the shoulder 44. Hence the spindle 26 moves relative to the casing 10 under the action of the spring loading 36 to move the valve member 28 against the valve seat in the same way as previously described.

Claims (6)

1. A gas pressure cut-off device comprising an actuator operable to effect gas flow past the device, a movable detent engagable with the actuator to prevent operation thereof, and means movable under the influence of gas pressure within the device to free the detent and thereby permit operation of the actuator.

2. A gas pressure cut-off device as claimed in claim 1, in which the means movable under the influence of gas pressure within the device comprises a diaphragm arrangement.

3. A gas pressure cut-off device as claimed in claim 2, in which the said means also comprises a member connected to the diaphragm arrangement and with a surface, which is engagable with the movable detent and profiled in such a manner that on movement of the diaphragm arrangement the profiled surface moves in relation to the detent to a point where the detent can itself move in relation to, and thereby free, the actuator for operation.

4. A gas pressure cut-off device as claimed in claim 3, in which the movable detent comprises a roller engagable with an enlarged portion of the actuator to prevent operation thereof.

5. A gas pressure cut-off device as claimed in any one of claims 1 to 4, in which the actuator comprises a spindle attached to a loaded valve member.

6. A gas pressure cut-off device, substantially as hereinbefore described with reference to Figs. 1 and 2 or Fig. 3 of the accompanying drawing.