GB2176874A

GB2176874A - Relief valve

Info

Publication number: GB2176874A
Application number: GB08515425A
Authority: GB
Inventors: Anthony Dyche
Original assignee: Marconi Co Ltd
Current assignee: BAE Systems Electronics Ltd
Priority date: 1985-06-18
Filing date: 1985-06-18
Publication date: 1987-01-07
Also published as: GB8515425D0

Abstract

A detachable relief valve for use in flexible inflatable structures, e.g. life rafts and salvage floats, to protect against over-inflation or over-pressurisation due to decrease in ambient pressure or increase in working fluid temperature, comprises (a) a flexible flanged member 1 the flange 3 of which is sealed to the vessel wall around a relatively rigid aperture 5; (b) an annular mounting member 11 detachably secured, eg. by a half-turn screw-in-fixing, to the flange member 3; and (c) a valve closure member 13 mounted on the mounting member 11 and urged against it to seal the aperture by non-linear spring means 39. The valve provides rapid transition between fully closed and fully open. <IMAGE>

Description

SPECIFICATION Relief valve This invention relates to fluid valves and particularly to relief valves which normally remain closed in operation but which open in conditions of excessive pressure differential between the upstream and downstream sides.

Relief valves are frequently fitted in flexible inflatable structures (e.g., life rafts & salvage floats) to protect against over inflation or over pressurisation due to decrease in ambient pressure or increase in working fluid temperature. Currently used relief valves offer relatively low flow capacity causing high fluid pressure upstream of the valve during dumping. They are also difficult to repair or replace.

One object of the present invention is to provide a relief valve which provides a high flow relief for differential pressure in excess of a predetermined value, while sealing upstream from downstream regions at pressures below that value. A further object is to provide an easily detachable valve body for repair and replacement.

According to the present invention, a relief valve comprises a flange member having a flexible planar flange adapted to be sealed to a container wall, the flange member having a relatively rigid aperture portion, a mounting member adapted to be detachably fixed to the flange member and sealed thereto around the aperture, and a valve closure member mounted on the mounting member and adapted to be biased into engagement with it to close the aperture for pressure differential across the closure member of less than a predetermined value, and to open for pressure differential in excess of this value, the valve closure member providing a peripheral flow path through the valve in the open condition and the valve closure bias being provided by non-linear spring means arranged to produce a disproportionate increase in flow path cross-section for a pressure differential increase through the above predetermined value.

The spring means preferably comprises a stack of dished spring washers arranged alternately concave and convex so as to exert a compressive force between the mounting member and the valve closure member.

The spring washers may be mounted on a shaft between an adjustment member screwed onto the shaft and the valve closure member, the screwed shaft being in tension between the mounting member and the screwed adjustment member.

Alternatively, the spring washers may be retained on a shaft by a push-on fastener, which, having only a one-way adjustment, are factory positioned.

The flange member is preferably of plastics material incorporating a metal reinforcing member within the relatively rigid aperture portion, the metal reinforcing member being a perforated stainless steel tube or other corrosion-resistant highstrength material.

The mounting member and the valve closure member are preferably made of high conductivity metal.

The valve closure member may lie radially within an extension wall of the mounting member, a gap between the valve closure member and the extension wall forming a neck in the flow path when the valve is partly open whereby to increase the opening force acting on the valve closure member and hasten full opening of the valve. This extension wall may be detachable from or integral with the mounting member.

The valve closure member is preferably sealed to the mounting member by an annular sealing member trapped in a groove of dovetail cross section.

The mounting member may have a single-turn two-start thread attachment to the flange member and incorporate lugs to permit thread locking tie(s) to be utilised when assembled to the flange member.

A relief valve in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings, of which: Figure 1 is a cross sectional view on the axis of the assembled valve; and Figure 2 is a view, partly in section, of the valve as dis-assembled.

Referring to the drawings, a flange member 1 of plastics material, for example polyurethane, has a radial planar flange 3 which is of sufficiently thin section to enhance the basic flexibility of the material. This flange is adapted to be sealed to the wall of a vessel, life-raft etc. around a hole formed in the vessel wall. According to the material of the flange 3 and the vessel wall, it may be sealed by adhesive or radio-frequency welding to the vessel wall.

The inner periphery 5 of the flange member 1 is of substantial thickness to provide rigidity and incorporates a stainless steel tube 7 for the same purpose. A single-turn two-start screw thread 9 is formed on the inner face of the aperture to enable detachment of the main parts of the valve.

The detachable parts of the valve consist of a mounting member 11, a valve closure member 13 resiliently fixed to the mounting member, and a flow ring 15. These parts are removable as one from the flange member 1 by means of the screw thread on the flange member and a cooperating male thread on the mounting member.

Figure 2 shows the valve 11 & 13 removed as one from the flange member 1 and the flow ring 15 further detached.

Referring to Figure 1 again, the mounting member 11 is of high conductivity metal, for example, aluminium alloy and is generally annular. A shoulder 17 on the flange member 1 fits into a mating groove 19 on the mounting member when the latter is screwed up tight so as to engage and compress an '0 ring' seal 21 in the groove. As shown in Figure 2 the hole in the vessel wall 23 is cut to such a size that the edge of the vessel wall sits snugly against the shoulder 17.

Extending inwardly from the annulus of the mounting member 11 are three radial webs 25 spaced at 120" which support a central boss 27 from which the valve closure member 13 is mounted. This closure member is also of high conductivity metal such as aluminium alloy. A recess in the boss 27 carries the head 29 of a screw threaded shaft member 31 in the form of a bolt.

This shaft extends through a central boss 33 of the valve closure member 13 and into a screwed adjustment member 35 in the form of a circular nut.

Peg holes 37 in the nut provide means for rotating it.

Alternatively the member 35 may have a plane bore and be retained, in a factory-determined position, by a push-on fastener in the form of a dished spring washer having radial slits to provide internal teeth or tabs.

Between the nut 35 and the boss 33 a stack of dished spring washers 39 are carried on the shaft 31. The spring washers 39 are arranged alternately concave and convex relative to one axial direction and thus provide a spring-like compressive force.

The effect is to put the shaft 31 in tension and to urge the boss 33 and the remainder of the valve closure member 13 to the left in Figure 1. The plane surface of the mounting member 11 is thus engaged by the peripheral plane surface of the closure member 13 to provide the operational sealing surface of the valve. A good seal at this interface is ensured by an 0 ring 41 mounted in a dovetail section groove 43 in the mating surface of closure member 13. This dovetail section groove facilitates simple replacement of the '0' ring.

Sealing of the path around the shaft 31 is effected by an annular seal 45 trapped in a shoulder of the boss 33 by a flat washer 47 against which the spring washers 39 bear.

The flow ring 15, shown detached in Figure 2, is shaped to adjust the flow path of fluid when the valve is open. It forms an extension wall from the mounting member 11 and may be formed integrally with it.

The valve closure member lies radially within the flow ring 15 with an annular gap between the two which converts the flow from radial to axial when the valve is open.

In operation, the pressure within the vessel, or chamber, to the left of the valve in Figure 1 is normally insufficient to compress the spring stack.

When the pressure differential across the valve closure member 13 increases sufficiently, due perhaps to temperature increase within the vessel, or pressure drop outside, the internal force on the closure member 13 causes the spring washers to compress and the closure member 13 moves outwards so opening a peripheral gap and allowing the internal fluid to escape.

The relatively large diameter of the valve, in relation to the actual movement of the valve closure member 13, between approximately 10 and 20 to 1, provides a large flow path for a small excess of differential pressure. In addition, the compression of the spring stack is non linear, the stack tending to compress rapidly after initial movement.

A further feature causing an increased flow on opening is the presence of the flow ring. When the valve opens, the gap between flow ring 15 and valve closure member 13 causes a bottleneck in the flow path and increases the opening force on the closure member 13. The valve consequently opens faster than it otherwise would, and, in addition, the hysteresis between "cracking pressure differential"and "resealing pressure differential"is increased.

The valve is operable over a wide range of temperatures down to approximately -40 C, the high conductivity of the valve materials helping to prevent icing-up when operating under water and the consequent failure to re-close after operation.

Claims

1. A relief valve comprising a flange member having a flexible planar flange adapted to be sealed to a container wall, the flange member having a relatively rigid aperture portion, a mounting member adapted to be detachably fixed to the flange member and sealed thereto around the aperture, and a valve closure member mounted on said mounting member and adapted to be biased into engagement with it to close said aperture for pressure differential across the closure member of less than a predetermined value, and to open for pressure differential in excess of said value, the valve closure member providing a peripheral flow path through the valve in the open condition and the valve closure bias being provided by non-linear spring means arranged to produce a disproportionate increase in flow path cross-section for a said pressure differential increase through said predetermined value.

2. A relief valve according to Claim 1, wherein said spring means comprises a stack of dished spring washers arranged alternately concave and convex so as to exert a compressive force between said mounting member and said valve closure member.

3. A relief valve according to Claim 2, wherein said spring washers are mounted on a shaft between an adjustment member screwed onto said shaft and said valve closure member, the screwed shaft being in tension between the mounting member and the screwed adjustment member.

4. A relief valve according to Claim 2, wherein said spring washers are mounted on a shaft between an adjustment member located on said shaft by a push-on fastening member and said valve closure member, the shaft being in tension between the mounting member and the adjustment member.

5. A relief valve according to any preceding claim, wherein said flange member is of plastics material and incorporates a metal reinforcing member within said relatively rigid aperture portion.

6. A relief valve according to Claim 5, wherein said metal reinforcing member is a perforated stainless steel tube.

7. A relief valve according to Claim 1, wherein said mounting member and said valve closure member are made of high conductivity metal.

8. A relief valve according to any preceding claim wherein the valve closure member lies radially within an extension wall of said mounting member, and a gap between the valve closure member and the extension wall forms a neck in the flow path when the valve is partly open whereby to increase said opening force acting on the valve closure member and hasten full opening of the valve.

9. A relief valve according to Claim 8 wherein said extension wall is detachable from said mounting member.

10. A relief valve according to any preceding claim wherein said valve closure member is sealed to the mounting member by an annular sealing member trapped in a groove of dovetail cross section.

11. A relief valve according to any preceding claim wherein said mounting member has a singleturn two-start thread attachment to said flange member.

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