GB1593871A

GB1593871A - Pressure relief valves

Info

Publication number: GB1593871A
Application number: GB10236/77A
Authority: GB
Original assignee: Expo Safety Systems Ltd
Current assignee: Expo Safety Systems Ltd
Priority date: 1977-03-10
Filing date: 1977-03-10
Publication date: 1981-07-22
Also published as: NL7802625A; NO780810L

Description

(54) IMPROVEMENTS IN OR RELATING TO PRESSURE RELIEF VALVES (71) We, EXPO SAFETY SYSTEMS LIM ITED, of 6/7 Hardy's Close, Feltham Avenue, East Molesey, Surrey, KT8 9BQ, formerly of 4 Linkfield, Hurst Park, East Molesey, Surrey KT8 9SD, a British Company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The invention relates to a pressure relief valve.

A pressure relief valve is desirably arranged to open fully to provide an aperture of relatively large area for the flow of the pressure medium, immediately a predetermined pressure limit is reached.

In accordance with the invention, there is provided a pressure relief valve comprising a housing having therein a valve aperture between first and second chambers for connection in use respectively to fluid at a first pressure and to fluid at a second pressure lower than the first pressure, a valve member in the second chamber having a closed position for closing the valve aperture, means arranged to hold the valve member in the closed position by magnetic attraction until the first pressure sufficiently exceeds the second pressure to displace the valve member from the closed position against the magnetic attraction, and spring means applying to the valve member a bias to move the valve member towards the closed position sufficiently to enable the magnetic attraction to effect closure but insufficiently to effect closure without the magnetic attraction.

The invention will be more readily understood from the following illustrative description and the accompanying drawing, which is a sectional side view of a pressure relief valve embodying the invention.

The illustrated pressure relief valve comprises an inlet casing I and an outlet casing 2.

Each casing is a generally cup-like hollow member with a tubular side wall and an aperture in its end wall. The two casings are assembled together in use in any convenient way for example as shown by means of bolts 4 extending through apertures in an external flange at the free end of the side wall of the casing 2, the stems of the bolts being received in tapped holes in the side wall of the casing 1. An apertured partition wall or valve plate 6 is clamped between the casings, a seal being effected between the valve plate and the end faces of the side walls as by the illustrated sealing rings 8.

The valve plate 6 is provided with an aperture around which a valve seat is defined by an annular ridge 12 facing towards the outlet casing 2, and a valve member 14 is supported within the outlet casing 2 for cooperation with this valve seat. The valve member 14 comprises a sealing pad 15 for engaging the ridge 12, sandwiched between a keeper plate 16 of magnetically attractable material and a backing plate 18. The sealing pad is of resilient material to ensure a good seal, and it and the backing plate are of greater diameter than the ridge 12, the keeper plate being of smaller diameter than the valve seat. The valve member is held together by a bolt 19 the head of which is received in a recess in the outer surface of the keeper plate so as to be flush with this surface.

The valve member is supported for movement of the sealing pad 15 toward and away from the ridge 12 by spring means in the form of a spring strip 20 depending from a clamp assembly 22 by which its upper end is secured to the valve plate above the aperture.

The lower end of the strip 20 is secured against the backing plate 18 by a nut on the stem of the bolt 19.

In the absence of external forces, the spring strip 20 holds the valve member 14 with the pad 15 adjacent the ridge 12 but not in sealing engagement with it. Sealing is effected magnetically, as by a permanent magnet 30 of cylindrical form which is mounted within the casing I so as to have one end face parallel and close to the free face of the keeper plate 16. The spacing between the opposed faces of the magnet and the keeper plate, which determines the force by which the pad 15 is held against the ridge 12, and thus the pressure excess within the casing I over that within the casing 2 at which the valve will open, is preferably adjustable and the magnet is accordingly mounted on a threaded shaft 31 received in a tapped hole in the end wall of the casing 1, so that rotation of the shaft will alter the spacing. A lock nut 32 on the shaft secures the magnet in its selected position.

In use, the pressure relief valve is connected between zones between which a predetermined pressure difference is not to be exceeded. The higher pressure, for example superatmospheric pressure, zone communicates with the casing 1 and the lower pressure zone, typically at atmospheric pressure, communicates with the casing 2. As soon as the pressure difference across the valve member 14 exceeds the upper limit, the valve member moves away from the valve seat and the magnet, allowing the pressure medium to flow from casing I to casing 2. Because the opening movement of the valve member 14 is away from the magnet 30, this exerts a restoring force which progressively decreases as the valve member moves, so that the valve opening movement is immediate and complete.When pressure equalization is reached, the valve member 14 returns under the light restoring force of the spring strip 20 towards the magnet, the progressively increasing attraction this exerts ensuring prompt restoration of a positive seal between the sealing pad 15 and the ridge 12.

The use of magnetic attraction to hold the valve member closed against the valve seat ensures that when the pressure difference on the two sides of the valve member causes this to break from the seat, a large flow aperture for the excess pressure is immediately obtained because the magnetic restoring force decreases as the valve member moves away from the seat. Valve opening movement is not against a constant or increasing restoring force but against a decreasing one.

The valve can include if desired any appropriate means for sensing the operation of the valve to provide pressure relief. Thus a proximity switch can be positioned in one or other of the casings to respond to the departure of the valve member from the closed position or its arrival at an open position. A differential pressure switch could be employed instead.

In an alternative arrangement for sensing operation of the pressure relief valve, the resulting pressure medium flow is directed through a whistle or other device which responds to the flow by producing a sound.

The resultant sound of course gives audible warning of valve operation and an electrical output signal can be obtained from it by provision of a microphone in or near the device. The volume of sound and thus the microphone output will increase with increasing flow of the medium through the sound producing device, so both the sound and the signal afford an indication of flow. A sensing device of this kind has applications other than in connection with the present or other kinds of pressure relief valve, for example, in the monitoring of a continuous gas flow for any purpose.

The electric signal obtained from any such sensing device provided can be applied to provide a visual and/or aural warning and/ or to exercise a control function.

A pressure relief valve embodying the invention is particularly but not exclusively suited for use in safety arrangements for electrical equipment required to operate in zones in which a spark from the equipment might explode a hazardous gas. The equipment is confined within an enclosure kept at super-ambient pressure so that the ignitable gas cannot enter it, and the valve can be associated with the enclosure to ensure that the excess pressure therein does not exceed a desired limit.

The pressure relief valve described can of course be modified in a variety of ways within the scope of the present invention as defined in the claims belows.

WHAT WE CLAIM IS: 1. A pressure relief valve comprising a housing having therein a valve aperture between first and second chambers for connection in use respectively to fluid at a first pressure and to fluid at a second pressure lower than the first pressure, a valve member in the second chamber having a closed position for closing the valve aperture, means arranged to hold the valve member in the closed position by magnetic attraction until the first pressure sufficiently exceeds the second pressure to displace the valve member from the closed position against the magnetic attraction, and spring means applying to the valve member a bias to move the valve member towards the closed position sufficiently to enable the magnetic attraction to effect closure but insufficiently to effect closure without the magnetic attraction.

2. A pressure relief valve as claimed in claim 1 wherein the spring means comprises a spring strip by which the valve member is mounted within the housing.

3. A pressure relief valve as claimed in claim 2 wherein the valve member is suspended by the spring strip from a position above the aperture on a wall of the housing in which the aperture is formed.

4. A pressure relief valve as claimed in claim 1, 2 or 3 wherein the means arranged to hold the valve member in the closed position comprises a permanent magnet in the first chamber.

5. A pressure relief valve as claimed in claim 4 wherein the permanent magnet is carried by a shaft extending through an outer wall of the housing, the magnet being mov

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. which the valve will open, is preferably adjustable and the magnet is accordingly mounted on a threaded shaft 31 received in a tapped hole in the end wall of the casing 1, so that rotation of the shaft will alter the spacing. A lock nut 32 on the shaft secures the magnet in its selected position. In use, the pressure relief valve is connected between zones between which a predetermined pressure difference is not to be exceeded. The higher pressure, for example superatmospheric pressure, zone communicates with the casing 1 and the lower pressure zone, typically at atmospheric pressure, communicates with the casing 2. As soon as the pressure difference across the valve member 14 exceeds the upper limit, the valve member moves away from the valve seat and the magnet, allowing the pressure medium to flow from casing I to casing 2. Because the opening movement of the valve member 14 is away from the magnet 30, this exerts a restoring force which progressively decreases as the valve member moves, so that the valve opening movement is immediate and complete.When pressure equalization is reached, the valve member 14 returns under the light restoring force of the spring strip 20 towards the magnet, the progressively increasing attraction this exerts ensuring prompt restoration of a positive seal between the sealing pad 15 and the ridge 12. The use of magnetic attraction to hold the valve member closed against the valve seat ensures that when the pressure difference on the two sides of the valve member causes this to break from the seat, a large flow aperture for the excess pressure is immediately obtained because the magnetic restoring force decreases as the valve member moves away from the seat. Valve opening movement is not against a constant or increasing restoring force but against a decreasing one. The valve can include if desired any appropriate means for sensing the operation of the valve to provide pressure relief. Thus a proximity switch can be positioned in one or other of the casings to respond to the departure of the valve member from the closed position or its arrival at an open position. A differential pressure switch could be employed instead. In an alternative arrangement for sensing operation of the pressure relief valve, the resulting pressure medium flow is directed through a whistle or other device which responds to the flow by producing a sound. The resultant sound of course gives audible warning of valve operation and an electrical output signal can be obtained from it by provision of a microphone in or near the device. The volume of sound and thus the microphone output will increase with increasing flow of the medium through the sound producing device, so both the sound and the signal afford an indication of flow. A sensing device of this kind has applications other than in connection with the present or other kinds of pressure relief valve, for example, in the monitoring of a continuous gas flow for any purpose. The electric signal obtained from any such sensing device provided can be applied to provide a visual and/or aural warning and/ or to exercise a control function. A pressure relief valve embodying the invention is particularly but not exclusively suited for use in safety arrangements for electrical equipment required to operate in zones in which a spark from the equipment might explode a hazardous gas. The equipment is confined within an enclosure kept at super-ambient pressure so that the ignitable gas cannot enter it, and the valve can be associated with the enclosure to ensure that the excess pressure therein does not exceed a desired limit. The pressure relief valve described can of course be modified in a variety of ways within the scope of the present invention as defined in the claims belows. WHAT WE CLAIM IS:

1. A pressure relief valve comprising a housing having therein a valve aperture between first and second chambers for connection in use respectively to fluid at a first pressure and to fluid at a second pressure lower than the first pressure, a valve member in the second chamber having a closed position for closing the valve aperture, means arranged to hold the valve member in the closed position by magnetic attraction until the first pressure sufficiently exceeds the second pressure to displace the valve member from the closed position against the magnetic attraction, and spring means applying to the valve member a bias to move the valve member towards the closed position sufficiently to enable the magnetic attraction to effect closure but insufficiently to effect closure without the magnetic attraction.

able by manual operation of the shaft end externally of the housing for selective adjustment of the magnetic attraction.

6. A pressure relief valve as claimed in claim 1, 2, 3 or 4 wherein the magnetic attraction is selectively adjustable.

7. A pressure relief valve as claimed in any preceding claim wherein the valve member comprises a sealing member of resilient material for engagement with an annular ridge around the aperture.

8. A pressure relief valve as claimed in claim 7 wherein the sealing member is sandwiched between a backing plate and a magnetically attractable member received in the aperture in the closed position of the valve.

9. A pressure relief valve as claimed in any preceding claim having means for indicating a valve-opening movement of the valve member.

10. A pressure relief valve as claimed in claim 9 wherein the indicating means comprise a sound producing means responsive to flow of gas through the aperture.

11. A pressure relief valve as claimed in claim 10 having a microphone arranged to provide an electrical output in response to sound produced by the sound producing means.

12. A pressure relief valve substantially as herein described with reference to the accompanying drawings.