GB2530094A

GB2530094A - Valve assembly

Info

Publication number: GB2530094A
Application number: GB1416253.1A
Authority: GB
Inventors: Christopher James Gurney; Paul Leonard Adcock; Jignesh Karsan Devshi Patel; Jodie Ball
Original assignee: Intelligent Energy Ltd
Current assignee: Intelligent Energy Ltd
Priority date: 2014-09-15
Filing date: 2014-09-15
Publication date: 2016-03-16
Also published as: GB201416253D0

Abstract

A butterfly valve assembly 200 comprises an inlet 204, an outlet 206, a valve chamber 208 having a passageway between the inlet and outlet, and a valve member 210 mounted within the valve chamber 208 and rotatable between open and closed positions. An edge of the valve member 210 defines a gap with an adjacent portion of a wall 202 of the valve chamber when in the open position, and the adjacent portion of the wall 202 includes a turn in a direction towards the edge, allowing for more sensitive control of fluid flow through the valve.

Description

Valve Assembly The disclosure relates to a valve assembly and in particular to a valve assembly having a rotary valve member such as a quarter turn or butterfly valve assembly.

Butterfly valves are generally known in the art for controlling flow in various applications involving fluids. Typically, such valves comprise a circular or elliptical disk rotatably mounted within a circular cross-section of a valve housing, where rotation of the disk between a closed position and an open position allows control over the flow of fluid through the valve.

Intelligent Energy Limited's patent GB 2464,936 discloses a butterfly valve comprising a valve body having an inner cylindrical fluid passage and a baffle. The baffle is elastically flexible to permit bending of its opposing vanes to separate a peripheral edge of the vanes from an inner surface of the valve body during rotation. The provision of a flexible baffle can allow for improved operation of the valve in freezing conditions by providing a progressive sheering action which causes the vanes to bend and pull away from the inner surface of the valve body when the valve is opened.

Valves are used in electrochemical fuel cell systems to control fluid-flow, such as airflow, and pressure. In some fuel cell applications it is necessary to provide precise pressure drop control at low mass flow rates or pressures. However, it has been found that it can be difficult to achieve the desired pressure control at low flow rates using conventional butterfly valves.

According to a first aspect of the invention there is provided a valve assembly comprising: an inlet; an outlet; a valve chamber having a passageway between the inlet and the outlet; a valve member mounted within the valve chamber and rotatable between an open position and a closed position, wherein an edge of the valve member faces and defines a gap with an adjacent portion of a wall of the valve chamber when in the open position, and wherein the adjacent portion of the wall is configured such that it includes a turn in a direction towards the edge.

This is advantageous as providing a valve chamber having a wall profile that turns in a direction towards the edge of the valve member can provide finer control of a gap or discharge area between the valve member and the valve chamber with rotation of the valve member, particularly at small rotation angles of the valve member.

The wall may be configured such that it curves as it extends along the passageway.

Thus, the turn towards the edge is provided by the curved profile of the wall.

Providing a curved valve chamber can allow the valve assembly to provide more refined io control of pressure drop across the valve. The curved chamber ensures that a gap between the valve member and an adjacent portion of the wall of the valve chamber gradually increases with angular displacement of the valve member from the closed position, thereby providing finer control of fluid flow through the valve assembly.

Is The adjacent portion of the wall may comprise a portion in which the edge of the valve member is spaced from the valve chamber (i.e. in the open position). Thus, the adjacent portion may not comprise the portion of the wall that faces the edge of the baffle in the closed position. The adjacent portion of the wall may curve towards the edge of the valve member. The adjacent portion of the wall may curve as it extends along the passageway away from the valve member. Thus, the profile of the adjacent portion and therefore the wall of the valve chamber tracks the edge of the valve member over its range of motion between open and closed positions but with increasing spacing. This increasing spacing provides the finer control of the valve's discharge area with respect to valve member angle from the closed position.

The valve member may be rotatable about a valve member axis transverse to the valve chamber axis between a closed position in which it occludes the valve chamber and an open position in which fluid flow is permitted through the valve chamber when in use.

It will be appreciated that the term width" does not impose any geometric or orientation limitations. That is, a height or depth may be considered to be a width herein. The width of the valve chamber may decrease as a function of distance along the passageway from the valve member axis. The valve member may have a radius defined by its length from the valve member axis. The width of the valve chamber may decrease as a function of distance from the valve member axis within the valve member radius. The width of the valve chamber may decrease as a function of distance along the valve chamber axis. The width may be a cross-sectional diameter. The width may be perpendicular to both the valve member axis and the valve chamber axis.

The provision of a valve chamber of decreasing width along its length allows a gap between the valve member and an adjacent portion of the wall of the valve chamber to gradually increase with angular displacement of the valve member, thereby improving fine control of fluid flow through the valve assembly. Controlling the rate of increase in the gap with respect to the angular displacement of the valve member using the internal profile of the valve chamber provides an effective means for precise pressure control.

The valve chamber may have a circular cross-section transverse to the chamber axis at a cross-sectional plane extending along the valve member axis. The valve chamber may have an elliptical profile in the direction of the chamber axis which describes an arc of increasing radius relative to the valve member axis such that a peripheral edge of the IS valve member gradually increases in distance from a wall of the valve chamber when the valve member rotates about its axis from the closed position to the open position. The distance of separation between the peripheral edge of the valve member and the wall of the valve chamber may increase with angle of rotation of the valve member as a function of the curvature of the wall of the valve body. The valve member may be circular. The valve chamber may have circular cross-sections of diminishing radius as the distance from the valve member axis increases. The valve assembly may comprise a seat. The cross sectional distance may decrease as a function of distance along the chamber axis from the seat. The valve assembly may comprise a quarter turn valve. The valve may comprise a butterfly valve. The valve member may comprise a vane either side of the valve member axis. The turn or curve in the wall may be provided at or over a portion of the valve chamber adjacent to the edge at an open position up to 45°, 30° or 200. It will be appreciated that one or more turns or curves may be provided in the wall to provide a particular discharge area versus opening angle profile.

According to a further aspect of the invention there is provided a fuel cell assembly comprising a valve assembly as disclosed herein.

The invention will now be described by way of example, and with reference to the enclosed drawings in which: figure 1 a shows a schematic cross-sectional view of a known cylindrical valve assembly; figure lb shows a portion of the schematic cross-sectional view of the valve assembly of figure 1 a in further detail; figure 2a shows a schematic cross-sectional view of an improved valve assembly; figure 2b shows a portion of the schematic cross-sectional view of the valve assembly of figure 2a in further detail; figure 3 shows a schematic cross-sectional view of another improved valve assembly; figure 4 shows a schematic cross-sectional view of a further improved valve assembly; to figure 5a shows a transverse schematic cross-section of the valve assembly of figures la and ib; figure 5b shows a transverse schematic cross-section of the valve assembly of figures 2a and 2b; figure 6a shows pressure drop versus valve member displacement angle profiles for a cylindrical valve assembly such as that illustrated in figures 1 a and 1 b; and figure 6b shows pressure drop versus valve member displacement angle profiles for a valve assembly such as that illustrated in figures 2a and 2b.

Figures la and lb show schematic cross-sectional views of a valve assembly 100.

Figure la illustrates a view of the entire valve assembly 100 showing the valve body 102 with an inlet 104 and an outlet 106.

A valve chamber 108 is defined within the body 102 and extends between the inlet 104 and the outlet 106. A chamber axis, x, is defined that extends in a direction along a fluid flow passageway between the inlet 104 and the outlet 106. In this example the valve body 102 is cylindrical and the chamber axis, x, is provided along the cylindrical axis of the valve body 102. The cylindrical valve body 102 has a constant cross sectional diameter, or width, w, in a cross-sectional direction, y, that extends normal to the chamber axis, x.

The valve assembly 100 also comprises a butterfly valve member, or baffle 110, that is pivotable, or rotatable, on a fulcrum 112 about a valve member axis, or baffle axis, z, that is transverse to (and in this example is perpendicular to) both the chamber axis, x, and the cross sectional direction, y. The baffle 110, which may also be referred to as a valve plate, comprises vanes that are planar (or flat) in this example and extend in opposing directions away from the fulcrum 155. The baffle 110 is rotatable between open positions and a closed position.

In the closed position the valve member 110 occludes the valve chamber 108 and so prevents fluid flow through the passageway between the inlet 104 and the outlet 106.

The valve member 110 has an edge that engages with a sealing portion of the wall of the valve chamber when in the closed position. The edge is provided at a radial extremity of the baffle 110. In this example, optional seats 114 are provided on the interior of the body 102 to engage with the baffle 110 in the closed position. The sealing portion of the wall is situated adjacent to the seat 114 and generally faces the edge of the baffle 110.

The closed position is typically provided at a 0° angular displacement, t, between the seat 114 and a face of the baffle 110 in which the plane of the baffle 110 is substantially aligned with the cross-sectional direction, y.

There are a range of open positions in which the edge of the valve member 110 defines a gap with an adjacent portion of the wall of the valve chamber, The adjacent portion can be considered to be a portion of the wall that generally faces the edge of the baffle when the baffle is in the open position, as will be discussed further with reference to figure 2b, below.

In the open positions, fluid flow is permitted along the passageway (through the valve chamber 108) between the inlet 104 and the outlet 106 of the valve body 102. In a fully open position, the effect of the baffle 110 on the flow of fluid through the passageway is minimised by aligning the plane of the vanes with the chamber axis, x, which is at an angular displacement, t, of around 90° from the closed position. In a partially open position, the baffle 110 is rotated by an angular displacement, t, between the fully open position and the closed position. Throttled fluid flow is permitted through the valve chamber 108 between the inlet 104 and the outlet 106 when the baffle 110 is in a partially open position.

Figure lb shows a portion 118 of the schematic cross-sectional view of the valve assembly 100 in further detail. Figure lb illustrates an arc 120 through which the baffle passes when it is moved from the closed position towards the fully open position.

In general, the size of a gap, g, between the baffle having a baffle radius, r, and the body 102 is given by: g = g0 + -r cosQ) where go is the zeroth gap between the end of the baffle and a wall of the body 102 in the closed position. Depending upon the seat geometry, the size of this zeroth gap, go, may limit the rate of flow through the valve.

In the closed position there is no flow and the baffle 110 is in contact with the seat. In this example, an edge of the baffle 110 faces, and is in contact with an interior of the body 102 when in the closed position and so the zeroth distance, go = 0 and r =w12. It will be appreciated that go may, alternatively, be greater than zero.

In a first partially open position the end of the baffle 110 isa first distance, gi, from the body 102. In a second partially open position the end of the baffle 110 is a second distance, g2, from the body 102. With the exception of the portion of the wall that faces the edge of the baffle in the closed position, the section of the wall of the valve body 102 illustrated in figure lb may be considered to be an adjacent portion 122 to the edge of the baffle 110 when the baffle 110 is rotated away from the closed position. A section of the adjacent portion 122 generally faces the edge of the baffle 110 when the baffle is in an open position.

Valves are used in electrochemical fuel cell systems to control fluid-flow, such as airflow, and pressure. In some fuel cell applications, it is necessary to provide precise flow control at low mass flow rates. However, it has been found that it can be difficult to achieve the desired pressure control at low flow rates using valve assemblies such as that illustrated in figures la and lb. Figures 2a and 2b show a schematic cross-sectional view of a valve assembly 200 provided with a valve body 202 that is curved in the direction of its axis. A corresponding series of reference numerals is used to identify corresponding features between figures 1 a and lb and figures 2a and 2b. Common features between the figures will not, in general, be discussed further.

Figure 2a illustrates a view of the entire valve assembly 200 showing a curved valve body 202 with an inlet 204 and an outlet 206. A fluid flow path between the inlet and the outlet is provided by a valve chamber 208 defined by the valve body 202. The valve assembly 200 may be a butterfly valve or quarter turn valve assembly and can be used in inline applications to control gas or liquid flow. In this exemplary embodiment, the valve assembly 200 may be used to control fluid flow in an electrochemical fuel cell.

It has been found that the rate of change in pressure drop across a conventional valve is relatively high at small angular displacements from the closed position. This makes precisely controlling the flow rate at low mass flow difficult. The valve assembly 200 allows the rate of change of pressure at small angles to be reduced in order to provide better flow control.

The valve chamber 208 has an elliptical profile in the direction of the chamber axis. That is, the walls of the valve body 202 (or valve chamber 208) curve inwards as they extend along the passageway away from the valve member. The valve assembly 200 comprises a valve member, or baffle 210, which is arranged in a similar manner to the baffle in the valve assembly of figure 1. When the valve member is in the open position, an edge of the baffle 210 defines a gap with a generally adjacent portion of the wall of the valve chamber 208 that generally faces the edge of the baffle 210.

In this example, the valve member axis, or baffle axis, z, passes through a centre of the ellipse of the valve body 202. The elliptical profile of the valve body 202 describes an arc of increasing radius relative to the baffle axis, z. The arc is such that a gap between a peripheral edge of the baffle 210 and a wall of the valve chamber 208 (which may also be considered as a wall of the valve body 202) gradually increases when the baffle 210 rotates about its axis, z, from the closed position and through the open positions.

A width of the valve chamber 202 or a cross-sectional distance between the baffle axis, z, and a wall of the valve chamber 202 decreases as a function of distance along the chamber axis, x, from the baffle axis, z. The cross-sectional distance extends in the cross sectional direction, y, which is perpendicular to both baffle axis, z, and the chamber axis, x. A cross-sectional width of the ellipsoidal valve chamber 208 within the valve body 202 decreases as a function of distance along the chamber axis, x, from the baffle axis, z, within an opening arc defined by the radius, r, of the baffle 210. A wall of the valve body 202 is curved along its entire length in the direction of the chamber axis, x, within a baffle radius, r, from the baffle axis, z. The curvature of the wall is less than the curvature of an arc defined by the baffle radius, r. The inwardly curved valve body profile of the valve assembly 200 allows the size of the gap between the body 202 and the baffle 210 to increase more gradually over a larger angular displacement, t, of the baffle 210. In this way, the valve assembly 200 may enable more sensitive control of upstream (or downstream) flow, particularly at low (less than 30° or 20°) angular displacement of the baffle from the closed position. The valve assembly 200 may be used where it is necessary to control the upstream (or downstream) pressure of the flow through the valve. The geometry of the valve body 202 and the interaction between the valve body 202 and the baffle are discussed further with reference to figure 2b.

Figure 2b shows a portion of the schematic cross-sectional view of figure 2a in further detail. Figure 2b illustrates an arc 220 through which the baffle 210 passes when it is moved from the closed position towards the fully open position. The section of the improved valve assembly 200 shown in figure 2b relates to an equivalent section of the valve assembly described with reference to figure lb. As in figure lb1 with the exception of the portion of the wall that faces the edge of the baffle in the closed position, the section of the wall of the valve body 202 illustrated in figure 2b may be considered to be an adjacent portion 222 to the edge of the baffle 210 when the baffle 210 is rotated away from the closed position. A section of the adjacent portion 222 generally faces the edge of the baffle 210 when the baffle is in an open position. That is, the adjacent portion 222 does not comprise the portion of the wall that faces the edge of the baffle 210 in the closed position.

The adjacent portion 222 of the wall curves as it extends along the passageway away from the valve member 210 and curves towards the edge of the valve member 210. In general, the size of a gap, g, between the edge of the baffle 210 (which has a baffle radius, r) and the body 202 is given by: g = f(x) -r cos(t) The cross section, f(x), of valve body 202 is not constant and decreases along the length of the chamber axis, x, away from the position of the baffle axis, z. For an ellipse: f(x) = + I[i Jb2 where a is the point where the ellipse would extend across the chamber axis, x, and b is the radius in the cross-sectional direction, y, at the baffle axis, z. It will be appreciated that x = rsin(t), so in terms of the angular displacement from the closed position: r*sint As in figure 1 b, in the closed position there is no flow and the baffle 210 is in contact with the seat 214. An end of the baffle is a zeroth gap, or distance, go, from the body 202 in the closed position. In this example, the edge of the baffle 210 is also in contact with an interior of the body 202 in the closed position and so the zeroth distance, go, equals zero.

In a first, partially open position the end of the baffle 210 is a first distance, gi, from the body 202. In a third partially open position the end of the baffle 210 is a second distance, g2, from the body 202. From comparison of figures lb and 2b it can be seen that the corresponding distances are substantially less for the improved valve assembly given the same angular displacement. The result of this is that the valve assembly reduces the rate of change of pressure at small angles, or rather, the rate of pressure change of a given angular displacement of the baffle is reduced, leading to a lower pressure drop at that angle.

The use of an elliptical profile, rather than another curved profile, can simplify the calculation of open area for the valve assembly 200 and so simplify design of the valve assembly 200.

Control logic may be provided in order to operate the valve assembly in accordance with a required mass flow rate or pressure drop across the valve member. The control logic may set the angular displacement of the valve member in accordance with a looked-up or calculated baffle displacement angle that corresponds with the required flow rate.

The displacement along the chamber axis, x, at which the closed position is located can also be amended. In the case of the valve assembly of figure la and lb, the closed position is in the plane of the fulcrum at x = 0. However, by providing the body 202 such that the closed position occurs when the baffle plate 210 is transverse, but not normal to, the direction of fluid flow along the chamber axis, x, greater control of the valve operation may be achieved. That is, the closed position may be provided at an angle between the cross-sectional direction, y, and the chamber axis, x, in order to reduce the rate of change of valve open area at low displacement angles from the closed position of the vavle assembly 200.

Various modifications to the valve of figure 2 will be apparent to the skilled person. For example, the pivot axis, z, may be provided nearer to one wall than the opposite wall. In some examples, the pivot axis may be provided within a wall of the valve body. In such s examples, the baffle may be provided as a flap that pivots about the baffle axis, z. The cross section through the body may be rectangular and the valve member may also be rectangular, or may comprise a flap. Other shapes are possible provided that the valve body can turn towards the edge of the valve member in order to provide a smaller gap for a given displacement angle compared to a straight valve body.

The valve body 202 in the example of figure 2 has a circular cross-section transverse to the chamber axis, x, at a cross-sectional plane, y-z, that extends in the cross sectional direction, y and along the baffle axis, z, The valve body 202 may have circular cross-sections, in the y-z plane, of diminishing radius as the distance from the baffle axis, z, increases along the chamber axis, x.

Figure 3 shows a schematic cross-sectional view of another improved valve assembly 300. The valve assembly 300 has a curved valve body 302 with an inlet 304 and an outlet 306. The curved valve body 302 defines a curved valve chamber 308.

The valve chamber 308 houses a valve member 310 that is similar to the valve member of the valve assembly of figure 2 and is rotatable between an open position and a closed position. The valve body 302 may be provided by a curved pipe, which may have a square or rectangular cross section. For example, a rectangular-based cylindrical pipe may be bent so that a set of opposing walls of the pipe are parallel and follow a curve. In such an example, the valve member 310 may be rectangular. As with the example in figures 2a and 2b, the valve body 302 is curved on either side of the valve member mounting. However, in this example, the curvature of a wall of the valve body 302 on the inlet side of the valve member 310 is in an opposite direction to the curvature of the wall of the valve body 302 on the outlet side.

As in figures 2a and 2b, the valve member 310 has an edge that engages with a sealing portion of the wall of the valve chamber 308 when in a closed position. When the valve member 310 is displaced from the closed position to an open position, the edge of the valve member 310 defines a gap with an adjacent portion of the wall of the valve chamber 302. The adjacent portion of the wall is configured such that it curves as it extends along the passageway between the inlet 304 and the outlet 306 and is similar to that described in relation to figures 2a and 2b.

However, unlike the example in figures 2a and 2b, the width of the valve body 302 in the cross sectional direction, y, is generally uniform, irrespective of where the cross section is taken along the passageway between the inlet 304 and the outlet 306. That is, opposing, curved, adjacent portions of the walls of the valve chamber 308 are parallel.

Figure 4 shows a schematic cross-sectional view of another improved valve assembly 400. The valve assembly 400 has a valve body 402 comprising an inlet 404, an outlet 406 and defining a valve chamber 408. The valve chamber 408 defines a passageway between the inlet 402 and the outlet 404. The valve body 402 may be provided by a curved pipe that has a square or rectangular cross section. For example, a cylindrical pipe may be bent so that a set of opposing, portions of the walls of the pipe are parallel.

Unlike the example in figures 2a, 2b and 3, the valve body 402 is curved on the inlet side of the valve member 310 and is straight on the outlet side of the valve member 310.

A valve member 410 is rotatably mounted within the valve chamber 408. The valve member 410 in this example is provided by a flap with a valve member axis that extends along a wall of the valve body 402 (which may also be considered to be a wall of the valve chamber 408), along the passageway. The valve member 410 is configured to rotate between an open position and a closed position. In the closed position the valve member is engaged with an optional seat 414 that protruded from the wall of the valve body 402 into the valve chamber 408. The valve member 410 has an edge at its periphery furthest from the valve member axis, z. The edge 416 engages with a sealing portion of the wall of the valve body 402 (which in this example is provided by the seat 414) when in the closed position.

The edge 416 of the valve member 410 and an adjacent portion 418 of the wall of the valve chamber 402 together define a gap when the valve member 410 is in the open position. The size of the gap may be determined using the equations described above with reference to figure 2. The adjacent portion 418 of the wall 402 is similar to that described with reference to figures 2a and 2b and configured such that it curves as it extends along the passageway between the inlet 404 and the outlet 406. The adjacent portion 418 in this example is disposed over a distance of around a radius of the valve (which is similar to the width of the valve body 202) from the seat 414.

Figures 5a and 5b show transverse cross-sectional schematics of the valve assemblies of figures 1 and 2, respectively. Each cross section is taken through the valve body at an equal distance along the chamber axis, x, displaced from the baffle axis, y, at a point of minimal open area. The full thickness of the baffle along the chamber axis, x, is shown.

The baffle is at the same angular displacement from the closed position in figures 5a and 5b.

In figure 5a, a partial opening 522a can be seen between the valve body 502a and the baffle 510a. Fluid can flow through the partial opening 522a. In figure 5b, a restricted opening 522b can be seen between the valve body 502b and the baffle 510b. A restricted amount of fluid can therefore flow through the restricted opening 522b compared to the partial opening 522a, resulting in a lower mass flow rate for the given angular displacement of the baffle from the closed position.

Figures 6a and 6b show pressure drop versus valve angle profiles for the valves illustrates in figures 1 and 2.

IS

Figure Ba shows pressure drop versus valve angle profiles for a cylindrical valve such as that illustrated in figures la and lb. The various curves shown relate to different mass flow rates that increase from left to right. Conventional control logic for a cylindrical butterfly valve controls the valve based on valve open angle to govern mass flow. At small valve angles (less than 300) there is a high rate of change in the pressure drop across the valve corresponding to relatively small changes in angular displacement from the closed position for a given mass flow. The curves increase asymptotically at lower angles.

Figure 6b shows pressure drop versus valve angle profiles for a valve such as that illustrated in figures 2a and 2b. The pressure drop at low angles for corresponding mass flow rates is reduced from the profiles shown in figure Bb compared with those of figure Ba. At low angular displacement, the pressure drop against angular displacement profiles are relatively insensitive to the change in angular displacement and do not increase asymptotically as in figure 6a. As such, curved valve bodies such as those described with regard to figure 2a and 2b can provide a more gradual pressure drop for variation in valve angular displacement than cylindrical bodied valves. The valve assemblies illustrated in figures 3 and 4 also benefit from the advantages obtained by the provision of the curved valve body.

It will be appreciated that the precise geometry of the valve assembly may be tailored to suit individual applications. In such cases, testing or modelling of individual valves can be performed using conventional techniques in order to determine the characteristics of the valve. Such testing or modelling can allow the appropriate control logic to be implemented, The turn of the adjacent portion of the valve chamber wall could be provided by two or more straight, non-parallel sections where the junction between the two sections forms the turn. A combination of straight and curved sections could be provided to form the profile of the wall opposite the edge of the valve member. Further, the above discussion compares the gap between the valve member and the valve chamber in the embodiment of Figures la and lb and the other figures. However, a comparison could also be made between the discharge areas of the valve configurations.

The discharge area is the area of the restriction between the valve member and the valve chamber through which fluid flows when the valve is in an open position. The discharge area is therefore defined by the open area between the tip of the valve member and the valve chamber wall closest to the tip of the valve member. Thus, we provide a turn or profile in the valve chamber wall over part of the wall that defines the discharge area when the valve is in one of its open positions (i.e. with a non-zero discharge area).

Claims

Claims 1 A valve assembly comprising: an inlet; an outlet; a valve chamber having a passageway between the inlet and the outlet: a valve member mounted within the valve chamber and rotatable between an open position and a closed position, wherein an edge of the valve member faces and defines a gap with an adjacent portion of a wall of the valve chamber when in the open position, and wherein the adjacent portion of the wall is configured such that it includes a turn in a direction towards the edge.
2, The valve assembly of claim 1 in which the adjacent portion of the wall is configured such that it curves as it extends along the passageway.IS
3. The valve assembly of claim 1 or claim 2 in which the adjacent portion of the wall curves as it extends along the passageway away from the valve member.
4. The valve assembly of any preceding claim in which the valve member is rotatable about a valve member axis transverse to the valve chamber axis between a closed position in which it occludes the valve chamber and an open position in which fluid flow is permitted through the valve chamber when in use, wherein a width of the valve chamber decreases as a function of distance from the valve member axis.
5. The valve assembly of claim 4 in which the valve member has a radius defined by its length from the valve member axis and the width of the valve chamber decreases as a function of distance from the valve member axis within the valve member radius.
6. The valve assembly of claim 4 or claim 5 in which the width of the valve chamber decreases as a function of distance along the valve chamber axis.
7. The valve assembly of any of claims 4 to 6 in which the width is a cross-sectional diameter.
8. The valve assembly of any of claims 4 to 7 in which the width is perpendicular to both the valve member axis and the valve chamber axis.
9. The valve assembly of any of claims 4 to 8 in which the valve chamber has a circular cross-section transverse to the chamber axis at a cross-sectional plane extending along the valve member axis.
10. The valve assembly of any of claims 4 to 9 in which the valve chamber has an elliptical profile in the direction of the chamber axis which describes an arc of increasing radius relative to the valve member axis such that a peripheral edge of the valve member gradually increases in distance from a wall of the valve chamber when the valve member rotates about its axis from the closed position to the open position.
11. The valve assembly of any of claims 4 to 10 in which the valve member is circular and the valve chamber has circular cross-sections of diminishing radius as the distance from the valve member axis increases.
12. The valve assembly of any preceding claim in which the distance of separation between the peripheral edge of the valve member and the wall of the valve chamber increases with angle of rotation of the valve member as a function of the curvature of the wall of the valve body.
13. The valve assembly of any preceding claim in which the valve assembly comprises a seat and wherein the cross sectional distance decreases as a function of distance along the passageway from the seat.
14. The valve assembly of any preceding claim in which the valve assembly comprises a quarter turn valve.
15. The valve assembly of any preceding claim in which the valve comprises a butterfly valve, wherein the valve member comprises a vane either side of the valve member axis.
16. A fuel cell assembly comprising the valve assembly of any of any preceding claims.
17. A valve assembly as described herein with reference to figures 2a, 2b, 3, 4, 5b and 6Lm