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Patent Searching and Data


Title:
A VALVE
Document Type and Number:
WIPO Patent Application WO/2016/193652
Kind Code:
A1
Abstract:
A valve (101) for controlling the flow of a fluid, and more particularly, a valve comprising a pair of independently operable valve members (125, 126) disposed in series, is shown. The valve comprises a valve body defining an inlet (116) and an outlet (117), and a passage (124) extending through said body defining a flow direction between the inlet and outlet; and first and second valve members disposed in the passage, and respective first and second valve seats (135, 136) associated therewith said first valve member and associated first valve seat being positioned upflow of said second valve member and associated second valve seat; each said valve member being movable between a closed position and an open position and each said valve member being biased in said closed position in which the flow of fluid past the valve member is prevented; in which said first valve seat is positioned upflow of said first valve member, and in which said second valve seat is positioned downflow of said second valve member.

Inventors:
DIMMER, Paul Thomas (45 Ashley Lane, Moulton, Northampton NN3 7NH, GB)
Application Number:
GB2016/000113
Publication Date:
December 08, 2016
Filing Date:
June 06, 2016
Export Citation:
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Assignee:
DIMMER, Paul Thomas (45 Ashley Lane, Moulton, Northampton NN3 7NH, GB)
International Classes:
F16K15/06; F16L37/40
Foreign References:
GB1025633A1966-04-14
US20050155645A12005-07-21
US4232704A1980-11-11
US5796419A1998-08-18
Attorney, Agent or Firm:
BANFORD, Jonathan (Franks & Co Limited, Carlton House26 Billing Road, Northampton NN1 5AT, GB)
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Claims:
Claims

What we claim is:

1. A valve for controlling the flow of a fluid, the valve comprising:

a valve body defining an inlet and an outlet, and a passage extending through said body defining a flow direction between the inlet and outlet; and

first and second valve members disposed in the passage, and respective first and second valve seats associated therewith said first valve member and associated first valve seat being positioned upflow of said second valve member and associated second valve seat; each said valve member being movable between a closed position and an open position and each said valve member being biased in said closed position in which the flow of fluid past the valve member is prevented; in which

said first valve seat is positioned upflow of said first valve member, and in which said second valve seat is positioned downflow of said second valve member.

2. The valve of claim 1 , in which said first and second valve members are arranged in series along said passage.

3. The valve of claim 1 or claim 2, in which said first valve member is arranged to be movable from said closed position towards said open position by a flow of fluid through said passage from said inlet towards said outlet.

4. The valve of claims 1 to 3, in which said second valve member is arranged to be movable from said closed position towards said open position in a direction opposed to a flow of fluid through said passage from said inlet towards said outlet.

5. The valve of claims 1 to 4, in which said first and second valve members are biased towards said respective closed positions.

6. The valve of claims 1 to 5, further comprising biasing means configured to bias said first and second valve members towards said respective closed positions.

7. The valve of claims 1 to 6, in which said biasing means comprises a biasing member common to said first and second valve members.

8. The valve of claim 7, in which said common biasing member comprises a perforated mounting plate.

9. The valve of claim 7 or claim 8, in which said biasing member comprises a compressible spring. 10. The valve of claims 1 to 9, in which said first and second valve members each define a substantially circular enlarged disc shaped head portion having an elongate valve stem portion extending orthogonally from a first face thereof. 11. The valve of claim 10, in which said valve stem portion defines a hollow tubular rod.

12. The valve of claims 1 to 11 , in which said passage defines a linear path through said valve between the inlet and the outlet.

13. The valve of claims 1 to 11 , in which said passage defines an angled path through said valve between the inlet and the outlet.

14. The valve of claims 10 to 13, in which said first and second valve members further comprise sealing members of an elastomeric material arranged about said head portion.

15. The valve of claim 13, in which said sealing member comprises an O- ring.

16. The valve of any of claims 1 to 15, further comprising an opening member configured to contact said second valve member.

17. The valve of claim 16, in which said opening member is configured to transmit a force to said second valve member to displace said second valve member towards said open position.

18. The valve of claim 16 or claim 17, in which said opening member is detachable from said valve.

19. The valve of claims 16 to 18, in which said opening member is slidably inserted through said outlet.

20. The valve of claims 16 to 19, in which said opening member comprises an elongate conduit.

21. A valve substantially as described herein and with reference to the accompanying drawings.

Description:
A Valve

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to fluid control valves, and in particular, valves used to shut-off the flow of fluid.

2. Description of the Related Art

Valves are devices generally known in the art for controlling and regulating the flow of fluid along a pipeline by opening, closing, or partially obstructing the flow of fluid through the valve. A valve typically comprises a body defining internally a fluid passage, and a valve member interposed in the fluid passage to engage a valve seat. The valve member is generally operable from outside of the valve body, to alter its position or orientation relative to the through flow of fluid, to thereby vary the resistance it provides to the flow. A valve tends to have a range of flow rates as the valve member is actuated and its resistance to the flow changes, and may be used to modulate the rate of flow of fluid along a pipeline, known as throttling, or to prevent the flow entirely, known as shut-off. Valves are used in a number of different scenarios to control the flow of fluid as required.

A specific use of a valve is to shut-off the flow of fluid through a pipeline to isolate a part of a fluid system, for example, when disconnecting external equipment from the system, or to remove a component of a machine for maintenance. A valve in such a configuration is known generally as an 'isolation' valve and typically includes a control for manually actuating the valve member to close the valve to thereby prevent the flow of fluid through the valve in either direction. Closing an isolation valve effectively divides a fluid system, allowing, for example, one part of a system to be bled down to remove fluid, whilst allowing a second part of the system to remain in its operable pressurised state. Such a set-up has considerable advantages when considering a fluid system comprising a number of different units connected by pipelines, in that one unit may be disconnected from the system, for example to undergo routine maintenance, whilst allowing the remaining units to continue operation.

However, conventional isolating valves require manual input from an operative to actuate the valve member to its closed position and thereby seal the valve. Given this burden on the operative, it is common for such isolation valves to include a motorised actuator under the control of a central control unit to facilitate electronic actuation. However, such an automated system incurs a significant disadvantage in terms of installation cost, and so it is desirable to provide an automatic operation isolation valve having a relatively simpler construction. BRIEF SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided a valve for controlling the flow of fluid, the valve comprising a valve body defining an inlet and an outlet, and a passage extending through the body defining a flow direction between the inlet and outlet; and first and second valve members disposed in the passage, and respective first and second valve seats associated therewith; each said valve member being movable between a closed position and an open position; in which the first valve seat is positioned upflow of the first valve member, and in which the second valve seat is positioned downflow of the second valve member.

In a preferred embodiment the first and second valve members are arranged in series in the passage defined internally by the valve body, such that all fluid flowing through said passage encounters each valve member consecutively.

Preferably the first valve member is arranged to be movable from the closed position towards the open position by a flow of fluid through the passage flowing from the inlet towards the outlet. Moreover, it is preferable that the second valve member is arranged to be movable from the closed position towards the open position in a direction opposed to a flow of fluid through the passage flowing from the inlet towards the outlet.

Preferably the first and second valve members are biased towards their respective closed positions, such that the valve members default to a closed position in the absence of a displacing force.

The valve preferably further comprises a biasing means configured to bias the first and second valve members towards their respective closed positions. More preferably, the biasing means comprises a biasing member common to both said first and second valve members. The common biasing member may preferably comprise a perforated mounting plate so as to present a minimum restriction to the flow of fluid through the valve. In a particular embodiment, the biasing member includes a compressible spring.

In a preferred embodiment, the first and second valve members are of the type known generally as 'poppet' valves, and define a substantially circular disc shaped head portion having an elongate valve stem portion extending orthogonally from a first face thereof. More preferably, the valve stem defines a hollow tubular rod.

In a preferred embodiment, the passage defined internally by the valve body defines a linear path extending between the inlet and outlet. As an alternative, the passage may define an angled path extending through the valve body between the inlet and outlet.

The first and second valve members may further include sealing members of an elastomeric material arranged about the head portion. Preferably, the sealing members are O-rings.

The valve may further comprise an opening member configured to contact the second valve member. In an embodiment, the opening member is configured to transmit a force to the second valve member to displace the second valve member towards its respective open position.

Preferably, the opening member is detachable from the valve. In an embodiment, the opening member is slidably inserted through the outlet of the valve.

The opening member preferably comprises an elongate conduit suitable for carrying a flow of fluid. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows in section a valve of the present invention in which the first and second valve members are in respective closed positions;

Figure 2 shows in section the valve of Figure 1 in which the first and second valve members are in respective open positions;

Figure 3 shows in section the valve of the present invention in which the first valve member is in its closed position; and

Figure 4 is a perspective cut-away view showing partially the biasing member forming part of the valve.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENT

Figure 1

A valve apparatus for controlling the flow of fluid according to an exemplary embodiment of the present invention is illustrated in a side cross sectional view in Figure 1. The same valve is shown in different states in Figures 2 and 3.

In this environment the valve is configured as an isolation valve to control the flow of fluid between a fluid tank and an auxiliary component. Isolation valves such as valve 101 are used to shut-off the flow of fluid, such as a liquid, a gas, a slurry, or a granular particulate material, along a pipeline, for example, to regulate the flow of fluid between machines.

In the embodiment, valve 101 is configured as cartridge removably integrated within a connector 102. Valved connector 102 is installed through an aperture in the side wall of a tank 103 containing a reservoir of fluid, to facilitate attachment of ancillary components to the tank. In the specific embodiment illustrated, tank 103 is a fuel tank containing a reservoir of liquid fuel, for example, diesel, used to fuel an engine of a boat. Tank 103 is being employed as a part of a 'split' tank system, in which a plurality of relatively small capacity fuel storage tanks are used in place of a single tank having a larger capacity. Each tank in the installation may be equipped with a valved connector 102 to facilitate attachment of each tank in parallel to a respective inlet of a common fuel manifold, into which fuel from each tank in the installation is drawn and combined in the manner of a fuel rail. Fuel from the common manifold is then fed to subsequent components in the fuel system, for example, the fuel filter, and ultimately to the engine for combustion. Such an installation is used, at least in part, for environmental safety reasons, to minimise the volume of fuel spillage to the ocean in the event of a leak occurring in a tank.

Valved connector 102 comprises of a plug 104, in the form of a generally cylindrical tube, defining internally a cavity 105, and externally a threaded portion 106, with an annular flange 107 at an outer end. In the embodiment, plug 104 is constructed of stainless steel, which is not deformed or fatigued when heated, and is not susceptible to corrosion by diesel fuel. A sealing washer 108 is installed about the shank of the connector adjacent flange 107 to create a water tight seal between the flange and the exterior of the tank wall, and a union nut 109 is threaded along the shank of the plug until the flange is pressed firmly against the exterior wall. The outer end of plug 104 defines an annular collar 110, in the form of a generally L- shaped member protruding from the end, and received in a correspondingly shaped groove 111 in adapter 112. Adapter 1 2, in the embodiment, comprises of a coupling piece constructed of a plastics material, to facilitate releasable attachment of the valved connector to an inlet duct of a fuel manifold, as will be described further with reference to Figure 2.

Valve 101 is removable installed in the cavity inside plug 104 and interposed in the flow of fluid through the plug. Valve 101 has a generally cylindrical valve body comprising of cylindrical side wall 113 and end walls 114, 115. End walls 114, 115 define respectively inlet aperture 116 and outlet aperture 117, coaxially aligned at first and second ends of the body respectively, and including sealing O-rings 118, 119. The valve 101 is inserted into the cavity 105 in the plug 104 and its lower end is abutted against annular lip 120, which protrudes inwardly into the cavity from the side wall of the plug. The valve is secured in place in the plug by means of circlip 121 , which is received in a corresponding groove defined about the circumference of the plug interior. Further sealing O-rings 122, 123 are provided about the valve body to seal the valve body against the internal wall of the plug and prevent ingress of fluid therebetween. In this way, all fluid flowing through the plug is channelled through valve 101.

The valve body defines internally a cavity defining a passage 124 extending through the valve body communicating the inlet 116 with the outlet 117. Passage

124 thus guides fluid flowing through the valve between the inlet and outlet, defining the direction of flow of fluid therethrough. In the specific embodiment, passage 124 defines a linear path through the valve body between the inlet and outlet. This configuration is preferred as it presents the least restriction to the flow of fluid through the valve, optimising flow efficiency of the valve. It will be appreciated however that the passage may alternatively define a non-linear path through the body, for example an angled or curved path. The passage may be non-linear as a result of an angled valve body, for example, a right angled valve, or alternatively, the cavity may include intrusions, such as baffles protruding inwardly from the internal wall of the valve body into the passage to alter the direction of fluid flow, resulting in a passage that traverses around the baffles.

Valve 101 further includes first and second valve members 125, 126, disposed in the passage in a series configuration, which is to say that all fluid flowing through the passage between the inlet and outlet encounters each valve member consecutively, as contrasted to a parallel configuration of valve members in which the flow of fluid is divided therebetween. In the embodiment, valve members

125 and 126 are substantially identical and are of the type referred to generally as a 'poppet' valve, having an enlarged circular disc shaped head part 127, 128, and an elongate valve stem part 129, 130. A first side 131 , 132 of the head of the valve, the valve crown, presents a substantially flat circular surface, and integral valve stem 129, 130 extends from an opposite side of the head. In the embodiment, valve stem 129, 130 defines a hollow tubular member extending from the head to a distal end terminating in a blind aperture. Head part 127, 128 further defines a groove about its periphery forming a seat for a sealing O-ring 133, 134. In the embodiment, the sealing O-rings 133, 134 comprise of a resiliently deformable elastomer material, such as Nitrile rubber (MBR), which is resistant to chemical degradation.

Valve members 125, 126 releasably engage first and second valve seats 135, 136 respectively. In the embodiment, valve seats 135, 136 are defined by the inner surfaces of the valve body end walls 114, 115, which include an annular recess 137, 138 about the circumference of the inlet and outlet ports respectively. Recesses 137, 138 are closely matched in diameter to the diameter of said valve head portions 127, 28, such that the valve head portions are received snugly in the recess, with the first surface of the head portions abutted against the base of the recess and the sealing O-rings creating a fluid-tight seal around the head portion with respect to the walls of the valve seat recess, thereby closing said inlet and outlet ports 116, 117 respectively.

As illustrated the first valve seat 135 is positioned upflow of the head part of the first valve member 125, that is to say, the first valve seat is positioned closer to the inlet 116 of the passage 124 than the first valve member head. In this configuration, the movement of the first valve member 125 between the closed position and the open position, is such that the first valve member moves with the flow of fluid passing through the valve from the inlet to the outlet. Thus, the tendency of the first valve member is to be moved automatically to its open position under a flow of fluid through the valve from the inlet to the outlet, with the first valve member only returning to its closed position when the flow slows or stops, thus allow forward flow through the valve, but preventing reverse flow, as will be described further with reference to Figure 3.

Moreover, the second valve seat 136 is positioned in the passage 124 downflow of the head part of the second valve member 126. That is to say, that the second valve seat 136 is positioned closer to the outlet 117 of the passage 124, than the head of the second valve member 126. As a result, the flow of fluid through the passage between the inlet 116 and the outlet 117, is aligned with the movement of the second valve member from the open position to the closed position, i.e. counter to the movement from closed to open. Thus, a negative pressure gradient across the valve, a pressure gradient decaying from the inlet towards the outlet, which would otherwise tend to result in fluid flow through the valve, will act to move the second valve member to the closed position, and indeed exert firm pressure on the valve member in the closed position, thereby ensuring that the second valve member remains closed even with high fluid pressure bearing against it. As a result, and as will be described further with reference to Figure 3, the second valve member defaults to a closed position under forward flow of fluid through the valve, preventing uncontrolled discharge of fluid through the valve when a component is removed from the adapter 112..

Valve 101 further includes a biasing means in the form of biasing member

139, on which first and second valve members are slidably located. Biasing member 139 comprises generally of a mounting plate 140, in the form of a generally circular disc attached to the side wall 113 about its peripheral edge, and a shaft 141 through its centre, on which shaft said first and second valve members are slidably located. A pair of small compressible springs 142, 143, approximately equal in length are located around the shaft either side of the mounting plate and engage the underside of the valve head so as to force the valve members outwardly of said mounting plate. The configuration of the biasing member 139 is described further with reference to Figure 4.

Thus, in the assembly described, said first and second valve members are each movable between along a linear path that is coaxial with the inlet 116 and outlet 117, between a closed position, in which the valve member head portion 127, 128 abuts its respective valve seat 135, 136, and the flow of fluid past the particular valve member is prevented, and an open position in which the head portion 127, 128 is removed from its valve seat, and fluid flow is permitted. It should be noted that, whilst in the specific embodiment described herein, i.e. a fuel isolation valve, it is desirable for each valve member, when in its respective closed position, to prevent entirely fluid flow across the valve, in alternative embodiments it is desirable for the valve to have a minimum flow rate, i.e. the flow rate with the valve member in its closed position, that is greater than zero, and in such an embodiment the valve in its closed position would act to impede, but not entirely stop, the flow of fluid.

Figure 2

Valve 101 is shown in section in its 'in use' state in Figure 2, in which the first and second valve members are displaced away from their respective valve seats and occupy their respective open positions.

Adapter 112 has been detachably coupled to an opening member in the form of inlet plug 201 of a fuel manifold, and the inlet plug is retained in adapter 112 by means of resiliently deformable clips protruding inwardly from the walls of the adapter to engage corresponding grooves defined by the manifold duct. In this way, a secure connection between the fuel manifold and the connector is maintained, preventing the fuel manifold from being 'blown' off under pressure.

Fuel manifold plug 201 includes an elongate conduit 202 running axially along its centre and protruding from the head of the plug to define a nipple portion 203. Nipple portion 203, includes a plurality of apertures 204 in its side to allow fluid flow into the conduit, and is inserted through said valve outlet 117 and a fluid tight seal is formed with the edge of the outlet by O-ring 119. In the fully inserted position illustrated, the distal end of nipple 203 is arranged to contact the crown 132 of said second valve member head portion 128, transmitting a force applied inserting the conduit through the outlet to the second valve member, and displacing the second valve member from its valve seat towards its open position.

Thus, second valve member 126 is moved from its closed position in which the valve member head portion 128 occludes the outlet aperture 117, towards its open position in which the head portion 128 is removed from the valve seat, generally along the passage towards the inlet 116 in a direction opposed to a fluid flow passing through the passage from the inlet 116 to the outlet 117. This allows fluid communication between the fuel manifold 205 and the passage 124.

As a result of the movement of the second valve member towards its open position, a negative pressure differential is created across the valve, and the fuel contained in the tank 103 exerts a pressure on the first valve member 125 which causes the valve member to be automatically pressed back in the passage towards the biasing member, thereby compressing spring 142. This allows fuel to flow out of the tank, through the inlet 116 and past the first valve member 125, along passage 124, past the second valve member 126, and through the outlet 117, via conduit 202. Fluid flow through the valve is permitted so long as both the first and second valve members remain in their respective open positions. In the embodiment, both first and second valve members 125, 126 are biased by way of biasing member 139 and springs 142, 143 to default to their closed position. The closing of the valve members is thus controlled by the restorative force provided by compressible springs 142, 143, with fluid flow past the valve members occurring when the force exerted on the valve member against the springs exceeds the 'cracking' force. The force required, and thus the opening and closing of the valves may be manipulated by selecting springs having the desired spring constant.

Such is the configuration of the second valve member, as described previously, that removal of the manifold inlet duct 201 from the adapter 112, will remove the force exerted on the second valve member 126, which will, as a result of the inertia of the fluid flow, and the restorative force provided by the compressible spring 143, return quickly to its closed position, thereby ceasing the flow of fluid from the outlet. Without second valve member 126 being brought to bear against valve seat 136, removal of the manifold duct from the outlet would result in a high negative pressure gradient over the valve, and uncontrolled discharge of the contents of the tank through the valve into the environment.

The ceasing of fluid flow past the second valve member results in equalisation of pressure between the passage 124 and fuel tank 103, and as a result the first valve member 125 is returned to its closed position by the compressible spring 142, as will be described further with reference to Figure 3.

Figure 3

Valve 101 is shown again in side section in Figure 3. As illustrated, tank 103 has emptied of fuel, thereby removing the pressure exerted on the first valve member 125 by the head of fuel in the tank and causing the rate flow of fuel through the valve to decrease, and cease. As the force exerted on the first valve member 125 by the flow of fluid is reduced, compressible spring 142 is allowed to relax and return to its original extended length, thus automatically returning the first valve member 125 to its closed position, in which the valve head portion 127 abuts against the valve seat 135, and thereby closing the inlet 116.

Closing of the first valve member 125 isolates the fuel tank 103 from the remainder of the fuel system, thus ensuring that reverse fluid flow, i.e. flow of fluid through the outlet 117 towards the inlet 116, is prevented, which would otherwise occur using an unvalved, or one-way valved connector if a positive pressure gradient developed across the valve.

In the application described a positive pressure gradient would develop over the valve if the back pressure in the manifold 205 exceeded the pressure head of fuel in the tank 103. Such a situation may arise unexpectedly in the event of a fracture in fuel tank 103, resulting in leakage of fuel to the environment. In this case, other fuel tanks in the installation would continue to feed fuel to the manifold 205. With the greatest pressure gradient existing between the manifold and the ruptured fuel tank 203, fuel from the manifold would drain across the valve 101 into fuel tank 203, thus exacerbating the problem of leakage from the tank, and resulting in fuel starvation to the engine. Such an unexpected drop in fluid flow through the valve, highlights a further significant operational advantage of the invention over a manual operation isolation valve as is conventional, in which a delay would arise in between reverse flow through the valve beginning, and an operative attending to manually close the isolation valve.

The closing point of the first valve member can be manipulated by varying the spring constant of the spring 142, to set a minimum threshold for the rate of flow through the valve, below which the first valve member will revert to its closed position, thereby closing the valve. In the embodiment, compressible spring 142 is selected having a relatively low spring constant, i.e. exerting a relatively low restorative force on the first valve member. In this way, the valve member will tend to require only a relatively low cracking force, i.e. the force required to cause the valve member to move against the spring to its open position is low, and so the valve member will open under even a light pressure exerted by the fuel, allowing low flow rates and near complete draining of the tank. This is advantageous in the application concerned, in which fuel is fed to the manifold at a relatively low rate, and wherein even moderate restriction to the flow, or redundant fuel in the tank, is undesirable.

However, the spring constant is selected to be sufficiently high, i.e. the spring is sufficiently stiff, that when the flow rate from the tank is below a threshold minimum, for example, a flow rate of LOLJmin, the restorative force provided to the valve member is sufficient to overcome frictional forces et cetera, and return the first valve member quickly to its fully closed position.

Figure 4

A partial cut-away view of the components of valve 101 is illustrated in

Figure 4, to show the configuration of the individual components described with reference to Figure 1 in their entirety. The valve body side wall 113, first valve member 125, spring 142, and sealing O-rings 118, 1 19, 133 and 134 are omitted so that the components that are shown are more clearly in view.

In the embodiment, the biasing means is provided by the common biasing member 139, which comprises of perforated mounting plate 140, a central shaft 141 , and first and second compressible springs 142, 143 (first valve member spring 142 omitted). Perforated mounting plate 140 comprises of a substantially planar disc having a diameter matching the internal diameter of the valve body, i.e. the diameter of passage 124. In this way, mounting plate 140 is secured to the inner wall surface of said side wall 113 about its entire circumference by suitable attachment means, for example, by welding, and creates a fixed platform from which the first and second valve members extend. It will of course be appreciated that a number of alternative methods for fixing said mounting plate to the side wall exists, and indeed, in a different embodiment the mounting plate may form an integrally moulded part of said side wall.

The mounting plate 140 further includes cut-outs 401 , which extend through the plate, and through which fluid flowing through the valve may pass. It is preferred that the area of the cut-out sections in the mounting plate is maximised, so that the mounting plate presents the least restriction to fluid flowing across it, however, it is desirable that the mounting plate is still sufficiently strong and rigid as to allow correct operation of the first and second valve members, and so the structure of the mounting plate cannot be compromised to too great an extent.

Mounting plate 140 further includes a shaft 141 , in the form of a solid cylindrical rod having an outer diameter corresponding closely to the inner diameter of each said hollow valve stem 129, 130. Shaft 141 extends through the centre of the mounting plate and is secured to the mounting plate approximately equidistant along its length, leaving a stub to protrude a predetermined distance from either face of the mounting plate. The shaft thus provides a 'rail' to guide the first and second valve members between their closed and open positions, and maintains the correct orientation of the valve member w.r.t the passage and fluid flow.

Compressible springs 142, 143 are thus located about the central shaft in the mounting plate with their first inner ends bearing against the upper and lower surface of the mounting plate, and the first and second valve members 125, 126 are slidably located on the respective upper and lower stubs of shaft 141 , such that the shaft is partially received in the hollow valve stem portions. The dimensions of the valve stem portions 129, 130, shaft 141 , and compressible springs 142, 143, are selected such that at maximum extension the respective spring is nearly fully extended, and the valve head portion 127, 128 is firmly located in the recess 137, 138 of its respective valve seat 135, 136, and so that the shaft may be further inserted into the valve stem hollow to allow the valve member to be fully withdrawn from the valve seat into the open position.

It will of course be appreciated that a number of alternative biasing means, and/or configurations of a biasing member are suitable. For example, as an alternative to compressible helical springs, a pneumatic ram, or an elastomer element could be employed to provide the required restorative force to the valve members. In particular, for reason of simplicity, a single compressible spring could be used in place of two small springs, to provide common biasing to both first and second valve members. In particular embodiments it may even be desirable that compressible springs are used having a non-linear spring rate with respect to extension.

Furthermore, as described herein the particular embodiment of the invention presented by the Applicant includes 'poppet' style valves, which are opened by lifting an enlarged valve head from an associated valve seat. It will of course be understood though that a number of alternative valve members are well known, for example, flap, diaphragm, or floating ball valve members, and the invention should not be considered to be limited in its utility to any particular type of valve member.

Additionally, although the invention has been described with reference to valve members which move along a path that parallel with the long axis of the cavity in the valve body, the valve member could equally be slidably mounted to the side wall of the valve body, and configured to move along a path perpendicular to the side wall, to engage a valve seat diametrically opposed in the passage. In such an arrangement, both valve members could move in the same direction between their respective closed and open positions, with the passage through the valve including baffles or other intrusions so as to guide the flow of fluid alternately to the front and rear faces of the valve members as required.

Moreover, whilst a particular embodiment of the invention has been described in which the valve is configured as an outlet connector of a fluid tank, it will of course be appreciated that further applications of the invention exist. For example, in an alternative embodiment, the invention is configured as a valve for use in a plumbing circuit, such as a domestic water supply pipeline, or as a part of a toilet cistern et cetera. Equally, given that the configuration of the valve is substantially symmetrical about a line passing diametrically through the valve equidistant between its two ends, the valve could be deployed as a two way valve, in which the direction of flow of water across the valve is alternated, whilst maintaining the operation described herein.

The valve is described in a particular exemplary embodiment in which it serves to control the outflow of a fluid from a fluid reservoir contained in a tank. However, as will be clear to the skilled person, the valve may alternatively be interposed along a pipeline, for example, midway between two components of a machine, with a first portion of the pipeline coupled to the valve at the inlet, and a second portion of the pipeline coupled to the valve at the outlet. In this case, a number of known methods of coupling the pipeline to the valve exist, including threaded screw connectors, compression fittings, and the more permanent welding/brazing, and the valve apparatus may be suitably adapted according to the connection method employed.