GB2520995A

GB2520995A - Pressure relief Valve

Info

Publication number: GB2520995A
Application number: GB1321604.9A
Authority: GB
Inventors: David Bailey
Original assignee: Fort Valve Engineering Ltd
Current assignee: Fort Valve Engineering Ltd
Priority date: 2013-12-06
Filing date: 2013-12-06
Publication date: 2015-06-10
Also published as: GB201321604D0

Abstract

A pressure relief valve 10 comprises a valve body having an inlet 34, a valve seat 36, a valve closure member 38 engageable with the valve seat, and a spring 40 for biasing the valve closure member 38 into engagement with the valve seat 36. The valve further comprises a valve closure abutment member 54 and second springs 56, 58 for biasing the valve closure abutment member 54 into engagement with the valve closure member 38, thereby further biasing the valve closure member 38 towards engagement with the valve seat 36. Retaining means 92 retains the valve closure abutment member 54 in position against the force of the second springs 56, 58 when the valve closure abutment member 54 has been displaced a predetermined distance from the valve seat 36.

Description

PRESSURE RELIEF VALVE

The present invention relates to pressure relief valves.

Pressure relief valves are fitted to vessels carrying gases and liquids in order to allow venting of the contents in extreme circumstances such as an increased pressure due to fire engulfment, in order to prevent explosion of the vessel. The pressure relief valve is fitted to a port located in the wall of the fluid vessel and typically comprises a valve closure member which is biased towards engagement with an annular valve seat by means of a very strong spring or multiple compression springs within the housing of the valve. In the event that the pressure within the vessel to which the valve is fitted increases to a level which would otherwise cause a catastrophic increase in pressure within the vessel, the pressure on the valve closure member lifts it off the annular valve seat, against the restoring forces of the spring or springs, and allows the pressurised contents in the fluid vessel to be vented in order to reduce the pressure within the fluid vessel.

In some circumstances, spring-biased pressure relief valves are unsuitable for use. For example, when the pressure relief valve is used on a rail tank, a high set pressure is required when the tank is transporting cargo, in order to prevent surging of the liquid within the tank from opening the valve against the restoring forces of the spring or springs. In such circumstances, the valve closure member can be held in place by means of a shear pin or buckle pin, instead of using springs, which can be set to a higher pressure relief value which will still provide pressure relief in a potentially catastrophic situation but which will not open during transport as a result of surging of liquid within the tank.

I

One of the problems with such valves, however, is that once the shear pin or buckle pin has ruptured, the valve no longer provides a pressure relief function since it is effectively open.

It would be desirable to have a pressure relief valve which is resistant to opening as a result of liquid surge but which still provides a pressure relief function, at a lower pressure level, after the valve has first opened.

In accordance with the present invention, a pressure relief valve comprises a valve body having an inlet, a valve seat, a valve closure member releasably engageable with the valve seat, first biasing means for biasing the valve closure member towards engagement with the valve seat, a valve closure abutment member, second biasing means for biasing the valve closure abutment member towards abutment with the valve closure member, and thereby to further bias the valve closure member towards engagement with the valve seat, and retaining means configured to retain the valve abutment member in position against the force of the second biasing means and out of abutment with the valve closure member, when the valve closure abutment member has been displaced a predetermined distance from the valve seat.

In the pressure relief valve of the present invention, the valve closure abutment member is normally held in abutment with the valve closure member by the second biasing means. Consequently, in order for the valve closure member to be displaced from the valve seat, the applied force on the valve closure member must exceed the combined forces of the first and second biasing means.

However, if the valve closure member is lifted from the valve seat through a predetermined distance, the valve closure abutment member is retained in that position against the force of the second biasing means. Consequently, in order to lift the valve closure member from the valve seat, the applied force need only exceed the force of the first biasing means.

As a consequence, the combined forces of the first and second biasing means can be set to a value which prevents inadvertent opening of the valve due to liquid surge during transport. Once the pressure relief valve has opened for the first time by a predetermined amount as a result of excessive pressure within the vessel to which the valve is attached, the valve closure abutment member will be held out of abutment with the valve closure member and the valve will therefore still provide a pressure relief function at a lower value, as a result of the first biasing means acting on the valve closure member.

This can be important in circumstances when the vessel to which the valve is connected is in a fire engulfment situation, in which the valve set pressure needs to drop to a lower pressure, preventing the tank from exploding until most of the cargo has ejected. The fire which causes the increasing pressure within the vessel may not always act on the pressure relief valve directly, and consequently allowing the valve to reset to a lower opening value after its first opening provides an additional safety feature.

Preferably, the retaining means is releasable. This allows the pressure relief valve to be reset to allow the valve closure abutment member to re-engage the valve closure member and thereby provide pressure relief function at a higher value, as determined by the first and second biasing means Preferably, a portion of the valve closure abutment member is engageable with a etaining member boated at a predetermined vertical distance from the valve seat. In a preferred embodiment, the portion of the valve closure element which is engageable with the retaining member is elongate and preferably is also hollow. In one embodiment, the portion of the valve closure abutment member which is engageable with the retaining member comprises a tube, In one embodiment, the retaining member is engageable with a portion of the interior of the valve closure abutment member.

The valve closure abutment member preferably comprises a recess for receipt of the retaining means.

The retaining member may be mounted on a support member which is fixed with respect to the valve body.

Preferably, the support member is elongate.

In one embodiment, the support member is slidable with respect to the portion of the valve closure abutment member which is engageable with the retaining member. The support member may be slidable within the valve closure abutment member.

In one embodiment, the retaining member is seated in a recess in the support member.

The retaining member may be displaceable so as to be simultaneously seated in the recess in the support member and engaged with the portion of the valve closure abutment member, thereby preventing movement of the support member and the valve closure abutment member with respect to each other.

The pressure relief valve may further comprise abutment means within the support member in abutment with the retaining member.

The abutment member may be eUdably disposed wlihin the support member.

Preferably, the abutment member is elongate.

In a preferred embodiment, the abutment member comprises a recess for partially receiving the retaining member.

Preferably, the abutment member is biased in a predetermined direction, for example in a direction away from the valve seat.

In a preferred embodiment, the retaining member comprises a ball.

Preferably, the pressure relief valve comprises a plurality of retaining members.

The pressure relief valve may further comprise an elongate guide member connected to the valve closure abutment member.

In a preferred embodiment, the elongate guide member is configured to project from the valve body when the valve closure abutment member is retained in position by the retaining means.

By way of example only, a specific embodiment of the present invention will now be described with reference to the accompanying drawings in which: Fig. 1 is a perspective view of an embodiment of a pressure relief valve in accordance with the present invention; Fig, 2 is a plan view of the pressure relief valve of Fig. 1; Fig. 3 is a vertical cross section through the pressure relief valve of Fig. 1 looking in the direction of arrows CC of Fig. 2, with the valve in an initial, closed condition; Fig. 4 is a vertical cross section through the pressure relief valve of Fig. 1 looking in the direction of arrows CC of Fig 2, showing the valve in an open condition; and Fig. 5 is a vertical cross section through pressure relief valve of Fig. 1 looking in the direction of C-C of Fig. 2, showing a valve closure abutment member in a latched position.

Referring to the figures, a pressure relief valve 10 comprises a valve body having an annular securing flange 12 having planar upper and lower faces 14, 16 and eight equally angularly-spaced apertures 17 for securing the valve to a valve mounting pad (not shown) on a vessel tank. The valve body further comprises a generally cylindrical side wall 18 welded or cast to the upper face of the securing flange 12. The side wall 18 is provided with four identical equally angularly-spaced curved rectangular windows 20 adjacent to the upper face of the securing flange 12, defining four identical supporting legs 22. A cap 24 having a cylindrical wall 26 extending from the periphery of a circular end wall 28 is removably and screw-threadedly connected to the upper end of the cylindrical side wall 18 of the valve by means of interengaging screw threads 30 on the exterior face of the upper portion of the cylindrical side wall 18 of the valve body and on the interior face of the end portion of the cylindrical wall of the cap 24. A tamper-evident seal 32 is secured between the outer face of the cylindrical wall of the cap 24 and the cylindrical side wall 18 of the valve body.

As best seen in Figs. 3 to 5, radially inwardly of the cylindrical side wall 15, the securing flange 12 is formed into a valve passage having a frustoconicsl portion 34 which is contiguous with a cylindrical or tubular portion 35 which opens into the interior of the valve body. Radially outwardly of the cylindhcal passage 35.

the upper face 14 of the securing flange 12 is formed into a generally planar annular valve seat 36.

The valve seat 36 is engageable by a circular disc-like valve closure member 38 which is strongly biased into engagement with the valve seat 36 by means of a strong helical compression spring 40 extending between the inner face of the end wall 28 of the cap 24 and the upper face of the valve closure member 38. The valve closure member 38 comprises first and second valve closure portions 42, 44 which are releasably secured to one another by means of four equally angularly spaced countersunk bolts 46 to form the valve closure member 38.

The first valve closure portion 42 is in the form of a circular disc whose diameter is very slightly smaller than the inner diameter of the cylindrical side wall 18 so that the valve closure member 38 may be displaced out of engagement with the valve seat 36 against the restoring force of the spring 40. The second valve closure portion 44 sits in a recess 48 in the lower face of the first valve closure portion 42 opposite to that engaged by the spring 40. The recess 48 is stepped, having an internal annular shoulder 49, and a circular aperture 50 extends through the central portion of the first valve closure portion 42 and receives a complimentarily-shaped boss 51 on the second valve closure portion 44. The first and second valve closure portions 42, 44 cooperate, when assembled, to form an annular seal groove which receives an annual 0-ring seal 52, which is configured to abut the valve seat 36 when the valve is closed.

A circular discUke valve closure abutment member 54 is biased towards engagement with the upper face of the valve closure member 35 by means of two strong helical compression springs 56, 56 extending between the upper face of the valve closure abutment member 54 and a spring mounting plate 60 located within the cap 24. The spring mounting plate is a circular disclike plate 60 having a central screw4hreaded aperture 62 which is screw4hreadedly engaged cn the lower end of a mounting plug 64 which is itself screw4hreadedly received in a threaded aperture 66 of a mounting plate 66 which is in turn secured in an aperture 70 in the centre of the upper face of the cap by means of eight equally angularly spaced securing bolts 72. The mounting plug 64 is provided with an elongate longitudinally extending guide aperture 74, as will be explained.

The centre of the valve closure abutment member 54 is provided with a screw-threaded aperture 76 in which the lower screw-threaded end of a straight elongate guide rod 78 is screw-threadedly received. The upper end of the guide rod 78 is slidably received in the longitudinally extending guide aperture 74 of the mounting plug 64.

A first guide tube 80 is welded to the upper surface of the valve closure abutment member 54 and extends perpendicularly to a point approximately two-thirds of the height of the side wall 18 of the valve body. The upper end of the flrst guide tube 80 slidably receives the lower end of a second guide tube 82 of smaller diameter whose upper end is welded to the under surface of the spring mounting plate 60. An elongate sleeve 84 is slidably mounted on the guide rod and within the second guide tube 82 and is biased upwardly by means of a compression spring 86 located around the guide rod and extending between the lower end of the sleeve 84 and an annular plug 88 which closes off the lower end of the second guide tube 82 and which slidably receives the guide rod 78.

The elongate sleeve 84 is provided with a neck portion of reduced external diameter which forms an annular recess 90 in the outer surface of the sleeve.

The recessed portion receives four ball bearings 92, each of which partially extends through a corresponding aperture 94 of slightly greater diameter than the ball bearings and extending through the wall of second guide tube 82. The upper and lower ends of the annular recess 90 are inclined, whereby engagement of the ball bearings with the inclined portions urges the ball bearings radially outwardly. It will also be observed that the internal face of the first guide tube 80 is provided with an internally-recessed annular portion 96 of increased internal diameter.

Under normal conditions of use, the valve is in the condition shown in Fig. 3, in which the 0-ring seal 52 carried by the valve closure member 38 is held in sealing engagement with the valve seat 36. The valve closure member 38 is held in sealing engagement by means of the compression spring 40 acting directly on the upper face of the valve closure member 38 and by the force of the two further compression springs 56, 58 which act on the upper face of the valve closure abutment member 54 which in turn abuts the upper face of the valve closure member 38. Therefore, in order to lift the valve closure member 38 from the valve seat 36, the force applied to the under surface of the valve closure member 38 must exceed the restoring forces of the three compression springs 40, 56, 58.

When the force on the undersurface of the valve closure member 38 exceeds the restoring forces of the springs 40, 56, 58, then the valve closure member 38 is lifted from the valve seat 36. If the valve closure member 38 is only lifted slightly from the valve seat 36, then if the force applied to the undersurface of the valve closure member 38 falls below the restoring forces of the three springs 40, 56, 58, the valve closure member 38 is re-seated on the valve seat 36-As the valve closure member 38 is lifted from the valve seat 36, the first, outer guide tube 80 slides over the ball bearings 92 in both directions as the valve closure member 38 moves.

However, if the valve closure member 38 is lifted from the valve seat 36 sufficiently. as shown in Fig. 4 the ball bearings 92 will engage the internal annular recessed portion 96 of increased diameter on the inner face of the first guide tube 80 and will move out of engagement with the annular recess 90 on the elongate sleeve 84. In this position, the upper end of the elongate sleeve 84 is in engagement with the undersurface of the spring mounting plate 60, and the inclined lower end of the recessed portion of the sleeve 84 has engaged the ball bearings 92 and has urged the ball bearings 92 outwardly towards engagement with the internal annular recessed portion 96 on the inner face of the first guide tube 80. As shown in Fig. 4, the first and second guide tubes 80, 82 become locked with respect to one another, by engagement of the ball bearings 92 with the apertures 94 in the second, inner guide tube 82 and of the internal recess 96 in the first, outer guide tube 80. The ball bearings 92 are prevented from moving out of engagement with the annular recess 90 in the first, outer guide tube 82 as they are also engaged by a full-diameter portion of the sleeve 84, as shown in Figs. 4 and 5.

As shown in Fig. 5, when the valve closure member 38 is re-seated on the valve seat 36, the valve closure abutment member 54 is held in a position above the valve closure member 38. As can be seen from Fig. 5, in this condition the two springs 56, 58 acting on the valve closure abutment member 54 no longer have any influence on the valve closure member 38. Instead1 only the helical compression spring 40 acts on the valve closure member 38. Consequently, after the valve closure abutment member 54 has been latched in position out of abutment with the valve closure member 38, in order for the valve to open it is then only necessary for the force on the valve closure member 36 to exceed the force applied by the compression spring 40.

It will also be observed that when the valve closure abutment member 54 is latched or retained in the position shown in Fig. 5, the upper end of the guide rod 78 projects out of the top of the mounting plug 64, which provides a visual indication that the valve closure abutment member 54 has been latched out of abutment with the valve closure member 38 and that a smaller force is required on the valve closure member 38 in order to open the valve.

if desred, the pressure reflef vahie may be reset in order to reengage the vave dosure abutment member 54 with the vave dosure member 38, to provide the norma operation as described previou&y This is achieved by dispscing the elongate sleeve 84 downwardly1 which allows the four ball bearings 92 to assume their original positions, as illustrated in Fig. 3.

The invention is not restricted to the details of the foregoing embodiment. ii

Claims

CLAIMS1. A pressure relief valve comprising a valve body having an inlet, a valve seat, a valve closure member releasably engageable with the valve seat, first biasing means for biasing the valve closure member towards engagement with the valve seat, a valve closure abutment member, second biasing means for biasing the valve closure abutment member towards abutment with the valve closure member, and thereby to further bias the valve closure member towards engagement with the valve seat, and retaining means configured to retain the valve closure abutment member in position against the force of the second biasing means, when the valve closure abutment member has been displaced a predetermined distance from the valve seat.
2. A pressure relief valve as claimed in claim 1, wherein a portion of the valve closure abutment member is engageable with a retaining member located at a predetermined vertical distance from the valve seat.
3. A pressure relief valve as claimed in claim 2, wherein the portion of the valve closure element which is engageable with the retaining member is elongate.
4. A pressure relief valve as claimed in claim 3, wherein the portion of the valve closure abutment which is engageable with the retaining member is hollow.
5. A pressure relief valve as claimed in claim 4, wherein the portion of the valve closure abutment member which is engageable with the retaining member comprises a tube.
6. A pressure relief valve as claimed in claim 4 or claim 5, wherein the retaining member is engageable with a portion of the interior of the valve closure abutment member.
7. A pressure relief valve as claimed in any of claims 2 to 6, wherein the valve closure abutment member comprises a recess for receipt of the retaining means.
8. A pressure relief valve as claimed in any of the preceding claims, wherein the retaining member is mounted on a support member which is fixed with respect to the valve body.
9. A pressure relief valve as claimed in claim 8, wherein the support member is elongate.
10. A pressure relief valve as claimed in claim 8 or claim 9, wherein the support member is slidable with respect to the portion of the valve closure abutment member which is engageable with the retaining member.
11. A pressure relief valve as claimed in claim 10. wherein the support member is slidable within the valve closure abutment member.
12. A pressure relief valve as claimed in any of claims 8 to 11, wherein the retaining member is seated in a recess in the support member.
13. A pressure rehet vave as damed n dam 12, wheren the retanng member s dspaceabe so as to be smuftaneou&y seated n the recess n the support member and engaged wfth a pordon of the vahie dosure abutment member; thereby prevenfing movement of the support member and the vave dosure abutment member vth respect to each other.
14. A pressure relief valve as claimed in any of claims 8 to 13, further comprising abutment means within the support member in abutment with the retaining member.
15. A pressure relief valve as claimed in claim 14, wherein the abutment member is slidably disposed within the support member.
16. A pressure relief valve as claimed in claim 15, wherein the abutment member is elongate.
17. A pressure relief valve as claimed in claim 16, wherein the abutment member comprises a recess for partially receiving the retaining member.
18. A pressure relief valve as claimed in any of claims 15 to 17, wherein the abutment member is biased in a predetermined direction.
19. A pressure relief valve as claimed in claim 18, wherein the abutment member is biased away from the valve seat.
20. A pressure relief valve as claimed in any of claims 2 to 19, wherein the retaining member comprises a ball.
21 A pressure relief valve as claimed in any of claims 2 to 20, comprising a plurality of retaining members.
22. A pressure reef v&ve as camed n any of the precedng oaftns, further compri&ng an &ongate gukie member connected to the vave cosure abutment member.
23. A pressure relief valve as claimed in claim 22, wherein the elongate guide member is configured to project from the valve body when the valve closure abutment member is retained in position by the retaining means.

24 A pressure relief valve substantially as herein described with reference to, and as illustrated in, the accompanying drawings. I 5.