GB2287330A - Pressure-activated safety shut-off valve - Google Patents

Abstract

A shut-off valve unit for a combustible gas supply has a gas inlet (60) and a gas outlet (66) enabling gas to be supplied to a pressure regulator and also having a gas feedback inlet (34) communicating via a feedback line with the gas delivery line on the downstream side of the regulator, the valve unit comprising a sensing unit (24 to 30) having a spring loaded valve member (26) which is fractionally moved against the spring pressure in response to pressure rise at the feedback inlet thereby to cause the feedback pressure to be applied to the whole cross section of the member (26) to snap open the valve member (26). This allows the feedback pressure to be applied to a piston (42) which operates a closure means (52 to 58) which closes the gas passage (60, 62, 66) through the unit. <IMAGE>

Description

Pressure-Activated Safety Shut-off Valve This invention relates to a pressure activated safety shutoff valve, in particular for a combustible gas supply system of the type which has a pressure regulator to which the gas is supplied on the upstream side and from which the gas is delivered to the point of use on the downstream side.

Typical of a gas supply system with which the invention is concerned is a system which supplies acetylene gas from pressurised bottles to welding or cutting equipment. In such a system, it is a requirement that the pressure on the downstream side of the pressure regulator should not rise more than a predetermined factor, of the order of 1.3, times the normal pressure, typically 1.5 bars. If such an excess and potentially dangerous excess pressure should develop, it is also required that the gas supply should be immediately shut down. For this purpose, it is known to provide a shut-off valve, sometimes referred to as a slamshut valve, on the upstream side of the pressure regulator.

Commonly, the shut-off valve is operated responsively to a feedback of the gas mixture from the downstream side of the pressure regulator.

It is an object of this invention to provide an improved shut-off or slam-shut valve.

According to the invention, there is provided a shut-off valve unit for a combustible gas supply system of the type above-described, the shut-off valve unit having a gas inlet and a gas outlet to enable the gas to be supplied to the pressure regulator and also having a gas feedback inlet for communication with the gas delivery line on the downstream side of the pressure regulator, said shut-off valve unit comprising a sensing device including a spring loaded valve member which is fractionally moved against the spring loading in response to a predetermined rise in pressure at the feedback inlet, thereby to open passage for the pressure of the feedback gas to be applied to snap open the valve member and thereby operate a slam-shut closure means which immediately fully closes passage through the unit from the gas inlet to the gas outlet.

Preferably, the excess pressure required to cause movement of the spring loaded valve member is determined solely by the spring force acting on said member, so that a constant loading force is applied at all times.

Thus, in an embodiment, the spring loaded valve member comprises an inner piston slidable in a cylinder outside of which is an outer piston slidable in a chamber in the body of the valve unit1 the inside of the cylinder behind the inner piston housing a calibrated spring acting on said inner piston and being sealed. The pressure inside the cylinder behind the inner piston is thus constant except for a very small pressure increase which takes place when the inner piston fractionally moves consequential on an exposed face of said inner piston being subject to an excess pressure rising above the calibrated spring loading. The fractional movement of the inner piston is sufficient to enable the said excess pressure to be applied past a cup seal to the whole cross-sectional area of the inner piston, so that the inner piston immediately snaps fully open against the spring loading.This opens a port in the cylinder wall to the outer piston, which thus slams to the end of its possible travel in the valve unit body, driving a plunger having a valve head which closes against a seating to shut off the valve supply. The plunger preferably has seals on opposite sides of a gas chamber through which the high pressure gas supply is fed from the gas inlet to the gas outlet, whereby the plunger is subject to balanced forces in opposite axial directions and exerts no load on the outer piston.

Many existing shut-off or slam-shut valves are nonresettable and have to be replaced after operation.

However, the pressure-activated shut-off valve unit above described can be readily reset, after the fault which caused operation has been rectified.

For this purpose, a manually operable reset pin is provided to act on the above-described inner piston, and the plunger is directly or indirectly manually accessible to push back the outer piston.

Thus, by depressing the reset pin to move the inner piston against its spring loading and, while maintaining the pin in its depressed condition, manually depressing the plunger, it is possible to restore the outer piston to its starting condition, the excess gas pressure acting on the outer piston being relieved via the air passage in the cylinder and the depressed inner piston.

The invention also relates to a gas supply system incorporating the above-defined shut-off valve unit.

An embodiment of the invention is now described by way of example with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram of a typical gas supply system for use in supply of a gas to welding or cutting equipment; Figure 2 is an axial cross-section through a shat-off valve; and Figure 3 shows a modification.

Referring first to Figure 1, acetylene gas stored in bottles 10, 14 is delivered through a pressure regulator 16 to the point of use 18, e.g. to operate welding or cutting equipment. The illustrated gas supply system is wholly conventional, and includes a safety shut-off valve 20 upstream of the regulator 16. A gas pressure feedback 22 is taken to this shut-off valve 20 from the downstream side of the regulator.

An advantageous arrangement of shut-off valve unit in accordance with the invention is shown in Figure 2. It is required substantially instantly to shut down the gas supply if the pressure on the delivery side of the regulator rises to a value of substantially 1.3 times the normal gas supply pressure of about 1.5 bars. It is also necessary that the shut-off valve should be capable of containing an explosion within the unit, should one occur, generating a pressure of up to 1000 bars. The embodiment of shut-off valve unit now described is capable of satisfying these requirements.

The illustrated unit comprises a two-part valve body 24, 24A which at one end houses a sensor constituted by a piston 26 having a cup seal 28 normally sealed closed against the head of a cylinder 30. The cylinder 30 is fully sealed behind the piston 26, the sealing means 32, 33 including a ring seal 32 carried by the piston, and accommodates a calibrated spring which loads the piston 26 against movement against a feedback gas pressure, applied through inlet 34 and passage 36, 38 against the cup seal 28, not exceeding a predetermined value of about 1.3 x 1.5 bars.

The cylinder/piston arrangement above described is housed in a chamber 40 in the valve unit body 24 which also houses an outer cup-shaped piston 42. Space 44 in the chamber 40 provides for travel of the outer piston 42.

As soon as a feedback pressure exceeding the predetermined pressure develops and is applied to cup seal 28, the piston 26 fractionally moves against its spring loading, lifting the cup seal 28 from the cylinder head. Gas at excess feedback pressure is thus applied to the whole area of the piston 26 defined by the "0"-ring seal 32, snapping open the piston 26 to the end of its range of travel against the loading of the spring 27. Cylinder port or ports 46 are thereby opened to cause the excess gas pressure to be applied, via clearance 48, to all forwardly directed faces of the outer piston 42 which, having no loading, is immediately forced to the end of its range of permitted travel in the chamber 40. Seal 82 prevents any gas entering the space 44 behind the outer piston.

The outer piston 42 drives a plunger 52 principally housed at the other end of the valve unit body, which plunger has a valve head 54 which is forced tight against a seating 56 on a sub-housing 58 through which the plunger slidably extends, thereby to shut down the gas supply, which normally passes from inlet 60 (connected to the gas source) through chamber 62 and passage 64 to the outlet 66 (connected to the pressure regulator). It will be appreciated that the gas supply is instantaneously fully shut down virtually simultaneously with the slamshut movement of the outer piston 42. Seals 80 are important in relation to the plunger 52, ensuring that the high pressure gas supply passing through chamber 62 acts in balanced manner on the plunger, which is thus subject to no axial loading and applies no axial force to the outer piston 42.

Reset pin 68 having cap 70 protected by gaiter 72 enables the safety shut-off valve to be reset, when used in conjunction with a cap 74 provided on the end of the plunger 52 within gaiter 76. Thus, when the excess pressure causing fault has been rectified, by depressing and holding down the reset pin 68, inner piston 26 is forced back against its spring loading, so that restoration of the plunger 52 and outer piston 42 to their starting positions is enabled by relief of gas pressure on the forward side of the outer piston back through the port 46 and past the depressed inner piston to the feedback inlet 34, which communicates the delivery line to the point of use. Both reset devices may then be released to enable normal operation to recommence.

The substantial mass of the unitary valve unit body enables high explosive pressures, up to l000bars, to be contained within the unit, and the various seals shown in Figure 2 but not described in detail are also important in this respect.

A modification of the above-described arrangement is shown in Figure 3, wherein similar reference numerals are employed for similar parts.

In the modified arrangement of Figure 3, the seals 32, 33 are omitted to avoid "stiction" effects. Nevertheless, as far as operation of the device is concerned, the cylinder 30 remains effectively sealed behind the piston 26.

Additionally, a spring 90 is incorporated, acting on the plunger 52 to limit the force applied by the valve head 54 to the seating 56 to the force exerted by the spring.

Thirdly, a sintered filter 92 is incorporated at exit of the feedback gas inlet passage 36. This in effect prevents entry of decomposed gas, in particular decomposed acetylene, to the device. In consequence, adjacent seal 80 is repositioned.

Claims (10)

Claims

1. A shut-off valve unit for a combustible gas supply system of the type described, the shut-off valve unit having a gas inlet and a gas outlet to enable the gas to be supplied to the pressure regulator and also having a gas feedback inlet for communication with the gas delivery line on the downstream side of the pressure regulator, said shut-off valve unit comprising a sensing device including a spring loaded valve member which is fractionally moved against the spring loading in response to a predetermined rise in pressure at the feedback inlet, thereby to open passage for the pressure of the feedback gas to be applied to snap open the valve member and thereby operate a slam-shut closure means which immediately fully closes passage through the unit from the gas inlet to the gas outlet.

2. A valve unit according to claim 1, wherein the excess pressure required to cause movement of the spring loaded valve member is determined solely by the spring force acting on said member, so that a constant loading force is applied at all times.

3. A valve unit according to claim 2, wherein the spring loaded valve member comprises an inner piston slidable in a cylinder outside of which is an outer piston slidable in a chamber in the body of the valve unit, the inside of the cylinder behind the inner piston housing a calibrated spring acting on said inner piston and being sealed.

4. A valve unit according to claim 3, wherein the pressure inside the cylinder behind the inner piston is constant except for a very small pressure increase which takes place when the inner piston fractionally moves consequential on an exposed face of said inner piston being subject to an excess pressure rising above the calibrated spring loading, whereby the fractional movement of the inner piston is sufficient to enable the said excess pressure to be applied past a cup seal to the whole crosssectional area of the inner piston, so that the inner piston immediately snaps fully open against the spring loading.

5. A valve unit according to claim 4, wherein movement of the inner piston opens a port in the cylinder wall to the outer piston, which thus slams to the end of its possible travel in the valve unit body, driving a plunger having a valve head which closes against a seating to shut off the valve supply.

6. A valve unit according to claim 5, wherein the plunger has seals on opposite sides of a gas chamber through which the high pressure gas supply is fed from the gas inlet to the gas outlet, whereby the plunger is subject to balanced forces in opposite axial directions and exerts no load on the outer piston.

7. A valve unit according to any of claims 3 to 6, wherein a manually operable reset pin is provided to act on the inner piston, and the plunger is directly or indirectly manually accessible to push back the outer piston.

8. A valve unit according to claim 7, wherein, by depressing the reset pin to move the inner piston against its spring loading and, while maintaining the pin in its depressed condition, manually depressing the plunger, it is possible to restore the outer piston to its starting condition, the excess gas pressure acting on the outer piston being relieved via the air passage in the cylinder and the depressed inner piston.

9. A gas supply system incorporating the shut-off valve unit according to any of claims 1 to 8.

10. A shut-off valve unit substantially as hereinbefore described with reference to the accompanying drawings.