Patent Description:
Various forms of fluid flow control valves, which can be suitable for controlling the flow of liquids or gases, are known in the art. Such valves include on/off switching valves, pressure control valves and proportional flow control valves, and are generally actuated by an input actuator, which can be provided in the form of a solenoid. A solenoid may be used to generate a magnetic field which can exert a magnetic force on a moveable member to provide opening, closing and/or switching of the valve by selectively bringing a valve element into and out of contact with a valve seat. Such valves typically include a biasing member that generates a biasing force to oppose the magnetic force. Therefore, in the absence of a magnetic field from the solenoid, the biasing force maintains the valve in a normally open or normally closed position. The biasing force should be sufficient to counteract the pressure of fluid acting against the valve element in order to keep the moveable member in a desired position, such as a closed position. For valves in which there is a high pressure difference across the valve element, the biasing member is typically configured to provide a high biasing force to prevent inadvertent lifting or closing of the valve element. In order to switch the valve to a different position, such as an open position, a relatively high actuating force may be required to overcome the biasing force of the biasing member. This can result in an undesirable increase in the size of the valve assembly and/or the power requirements. A known way of reducing the sizes and/or strengths of the biasing member or actuator is to use pressure compensation.

<CIT> discloses a proportional flow valve comprising a valve shell assembly, an electromagnet assembly, a valve element assembly, a sealing ring structure and a pre-tightening force structure. <CIT> discloses an electromagnetic control valve having an electromagnetic driving section, an adjusting spring, a pressure equalizing chamber, and a diaphragm disposed opposite a valve port on an axis of the valve port. A tapered surface is formed in the lower end portion of the valve body, and a helical compression spring causes a sliding surface of a spring holding member to abut on the tapered surface. <CIT> discloses a valve having a valve body, a valve chamber, a valve device, a biasing element and a pressure compensation element.

The inventors have identified a need to modify known valve structures in order to permit the miniaturisation of valves and to allow for the smaller displacements and actuating forces which may be experienced when seeking to create a smaller sized valve having improved precision.

According to a first aspect of the invention, there is provided a valve assembly for a valve, comprising: a valve body having walls defining a valve chamber; a first fluid port; a second fluid port; a valve seat located between the first and second fluid ports; a moveable member comprising a valve element at its first end, an armature at its second end, and a shaft portion extending axially between the valve element and the armature, wherein the moveable member is moveable in an axial direction to bring the valve element into and out of engagement with the valve seat to selectively open and close the valve, and wherein the entire moveable member is spaced from the walls of the valve body when the valve is open or partially open; at least one biasing member configured to support and bias the moveable member in the axial direction; and a flexible membrane which forms a seal against the moveable member and the valve body to divide the valve chamber into a flow chamber in which the valve seat and valve element are located and a pressure compensation chamber within which the armature is entirely enclosed. The moveable member comprises one or more bores defining a pressure compensation flow path by which the first fluid port is fluidly connected to the pressure compensation chamber, the pressure compensation flow path having at least one opening extending into the pressure compensation chamber at an axial position between the armature and the flexible membrane. The pressure compensation flow path comprises: a first axial portion with a first length and a first cross-sectional area and a second axial portion adjacent to the first axial portion with a second length and a second cross-sectional area which is less than the first cross-sectional area. The first length is at least <NUM> percent of the second length. The valve element comprises a first axial bore and the shaft portion comprises a second axial bore, wherein the first axial portion of the pressure compensation flow path is defined by the first axial bore and the second axial portion of the pressure compensation flow path is defined by the second axial bore. The shaft portion and the valve element are discrete components which are fixed together with an interference fit.

In valves for precision applications, it can be particularly important to provide predictable, repeatable operation of the valve, which is resistant to undue influence by external factors such as supply pressure or flow rates, to ensure correct operation of equipment into which the valve is integrated. Such factors can be particularly important in micro-fluidic valves, since the smaller sizes of components and of the assembly mean that variations in component properties or valve operation can have a relatively large effect on the overall performance of the valve. One way of improving repeatability and resilience to external pressure variations is to provide a pressure-compensated valve.

The present disclosure seeks to improve the performance of known valves by optimising the pressure compensation flow path. By arranging the pressure compensation flow path to comprise at least one opening extending into the pressure compensation chamber at an axial position between the armature and the flexible membrane, and by forming the pressure compensation flow path from at least two axial portions having different cross-sectional areas, the flow characteristics of fluid in the pressure compensation flow path can be improved, resulting in an optimised valve which can be actuated with better precision. This differs from some existing arrangements in which the pressure compensation flow path terminates at an opening on the upper surface of the armature and away from the flexible membrane. In such valves, fluctuations in the fluid pressure changes at the first fluid port can take some time to be transmitted to the pressure compensation chamber side of the flexible membrane due to the distance between the opening and the flexible membrane or due to flow restrictions between the opening and the flexible membrane, such as a flow restriction between the walls of the pressure compensation chamber and the side edges of the armature. This delay can make accurate control of the valve more difficult, particularly when the valve is held in a partially open position by the solenoid. By providing the pressure compensation flow path with at least one opening extending into the pressure compensation chamber at an axial position between the armature and the flexible membrane, fluctuations in the fluid pressure changes at the first fluid port can be transmitted to the pressure compensation chamber side of the flexible membrane more quickly, since the fluid does not need to first flow over the top and around the sides of the armature. Further, by providing the pressure compensation flow path with a first axial portion with a first cross-sectional area and a second axial portion with a second cross-sectional area which is less than the first cross-sectional area, the inventors have found that the control accuracy of the valve can be further improved. Without wishing to be bound by theory, this is believed to be due to a funnelling effect as the fluid travels along the pressure compensation flow path and passes between the first and second axial portions. The first and second cross-sectional areas each define first and second hydraulic diameters. One or both of the first and second cross-sectional areas may be constant along substantially the entire length of the first and/or second axial portions. The first and second axial portions may have any suitable cross-sectional area, for example circular, oval, square, rectangular, or other regular polygon. Where the first and second axial portions have circular cross-sectional shapes, the first and second cross-sectional areas are defined by the first and second diameters of the first and second axial portions.

In some embodiments of the invention, the armature may be flat. As used herein, 'flat' describes the general shape of the armature as one which is elongate in a transverse direction. That is, an armature having a maximum transverse dimension which is greater than its maximum axial dimension. With this arrangement, the entire armature can be located beyond the axial end of the solenoid coil during use to provide a compact arrangement while still providing sufficient magnetic interaction between the armature and the solenoid coil. Further, by housing the armature entirely within the pressure compensation chamber, friction between the armature and other components of the valve can be reduced or eliminated entirely. This can be contrasted with some known armatures which comprise an axial rod that extends into the hollow core of the solenoid coil. The flat armature may have any suitable shape. For example, the flat armature may comprise an approximately disc-shaped component. The flat armature may have a circular cross-sectional shape. The flat armature may have a maximum transverse dimension which is at least twice the maximum axial dimension, or three times, or four times, or five times as great as the maximum axial dimension.

The moveable member may be a free-floating moveable member. In such arrangements, the entire moveable member is spaced from the valve body and from any actuator assembly with which the valve assembly is used. This can eliminate any friction between the moveable member and surrounding portions of the valve assembly to provide a more precise and longer lasting valve assembly. With a free-floating moveable member, the moveable member may be constrained only by the biasing member and the flexible member when the valve is in its open position. The moveable member may be free to oscillate about a lateral axis when the valve is in the open position, subject to the stiffness and/or compliance of the biasing member and the flexible member. When the valve is in its closed position, the moveable member may additionally be constrained by its contact with the valve seat.

The first length is at least <NUM> percent of the second length. That is to say, the first axial portion is at least one fifth as long as the second axial portion. Preferably, the first length is as large of a proportion of the second length as possible. In some embodiments, the first length may be at least <NUM> percent, or <NUM> percent, or <NUM> percent of the second length. This provides the advantage of maximising the length of the first axial portion of the pressure compensation flow path. Since the first axial portion has a larger cross-sectional area than the second axial portion, by increasing the length of the first axial portion relative to the second axial portion, the proportion of the pressure compensation flow path that is defined by a larger cross-sectional area is increased, which provides for improved flow characteristics.

The first axial portion is adjacent to the second axial portion. The first axial portion may be immediately adjacent to the second axial portion. The pressure compensation flow path may comprise a transition portion between the first axial portion and the second axial portion by which the cross-sectional area of the pressure compensation flow path gradually decreases from the first cross-sectional area to the second cross-sectional area. The transition portion may be sloped or curved. Alternatively, the pressure compensation flow path may comprise a step portion by which the cross-sectional area of the pressure compensation flow path decreases immediately from the first cross-sectional area to the second cross-sectional area.

The shaft portion and the valve element are discrete components, which are fixed together with an interference fit. A first end of the shaft portion may be press fit within the first axial bore of the valve element to fix the shaft portion to the valve element. This provides an arrangement in which the components of the moveable member can be secured together using an advantageous method of assembly.

The shaft portion may comprise at least one transverse bore in fluid communication with the second axial bore. The at least one transverse bore may form part of the pressure compensation flow path. The at least one transverse bore may define the at least one opening of the pressure compensation flow path. The transverse bore may extend substantially perpendicular to the axial direction of the moveable member. The shaft portion may comprise at least two, at least three, or preferably at least four transverse bores. This improves the pressure compensation characteristics of the valve assembly. In some arrangements, the shaft portion may comprise at least five or at least six transverse bores.

The shaft portion may comprise at least one transversely extending shoulder. At least one transverse bore may be defined in the at least one transversely extending shoulder. The shaft portion and the armature may be discrete components, preferably fixed together with an interference fit.

At least one opening may extend into the pressure compensation chamber at a position immediately adjacent to the flexible membrane. The at least one opening may be a plurality of openings. The flexible membrane may be planar.

Further features and advantages of the present invention will become apparent from the following description of embodiments thereof, presented by way of example only, and by reference to the drawings, wherein:.

A valve assembly is described herein in the context of a valve for controlling the flow of fluids, such as liquids or gasses. The valve assembly includes a valve body, defining a valve chamber, and a first fluid port and a second fluid port, through which fluid can flow between the valve and components into which the valve is integrated. The valve assembly further includes a moveable plunger which can be moved along an axis of the valve assembly. A valve element is provided in fixed relation to the plunger which can open or close a fluid path between the first and second fluid ports by engaging with a valve seat. The plunger is actuated by means of an armature comprised in the plunger in combination with a solenoid assembly. The solenoid assembly includes a coil of wire wrapped around a bobbin which can be energised in order to induce a magnetic field to thereby control the movement of the armature. A biasing member connected to the moveable member can provide a biasing force in the opposite direction to a magnetic force provided by the solenoid.

The valve assembly includes a pressure compensation mechanism. In this respect, the valve chamber is delimited from a pressure compensation chamber by a flexible membrane. The plunger includes a pressure compensation flow path which fluidly connects the first fluid port to the pressure compensation chamber in which the armature is located. The pressure compensation flow path has at least one opening extending into the pressure compensation chamber at an axial position between the armature and the flexible membrane. Furthermore, the pressure compensation fluid path includes a first axial portion with a first cross-sectional area and a second axial portion with a second cross-sectional area which is less than the first cross-sectional area.

Referring to the drawings, <FIG> shows a cross-sectional view of a valve <NUM> comprising a valve assembly <NUM> and an actuator assembly <NUM>. The valve assembly <NUM> comprises a valve body <NUM> defining a valve chamber <NUM>. The valve body <NUM> comprises a first fluid port <NUM> and a second fluid port <NUM> with a valve seat <NUM> located therebetween. The valve assembly <NUM> further comprises a moveable member <NUM>, typically referred to as a plunger. The moveable member <NUM> comprises a valve element <NUM> at its first end for selectively sealing against the valve seat <NUM>. The valve element <NUM> may comprise a transversely extending shoulder <NUM> which is seated against the valve seat <NUM> when the valve assembly <NUM> is closed. The moveable member <NUM> also comprises an armature <NUM> at its second end. The moveable member <NUM> is moveable in an axial direction along axis <NUM> to bring the valve element <NUM> into and out of engagement with the valve seat <NUM> to selectively open and close the valve. In this example, the armature <NUM> is a flat armature which is elongate in a transverse direction such that its maximum transverse dimension is greater than its maximum axial dimension. The armature <NUM> may be directly connected to the valve element <NUM>. In this example, the moveable member <NUM> further comprises a shaft portion <NUM> extending axially between the valve element <NUM> and the armature <NUM> to connect these two portions of the moveable member <NUM>. The moveable member <NUM> may be a single, unitary component such that the armature <NUM>, shaft portion <NUM> and valve element <NUM> are provided as different portions of a single piece. Alternatively, one or more of the armature <NUM>, shaft portion <NUM> and/or valve element <NUM> may be provided as separate, discrete component, as discussed below in relation to <FIG>.

The valve assembly <NUM> further comprises a biasing member <NUM> configured to support and bias the moveable member <NUM> in the axial direction. The biasing member <NUM> may be configured to bias the moveable member <NUM> towards a first of its open and closed positions. The biasing member <NUM> may comprise a spring, preferably a flat spring, such as a plate spring. The biasing member <NUM> may comprise a plurality of transversely extending biasing components. In the illustrated example, the biasing member <NUM> is configured to bias the moveable member <NUM> towards its closed position. In an alternative arrangement, such as one in which energising the coil <NUM> is configured to move the moveable member <NUM> towards its closed position, the biasing member <NUM> may be configured to bias the moveable member <NUM> towards its open position. In either case, the biasing member <NUM> is generally configured to exert a biasing force on the moveable member <NUM> in an axial direction opposite to the axial direction of the magnetic force provided by the solenoid. The biasing member <NUM> may be restrained against movement in the axial direction relative to the moveable member <NUM> and relative to the valve body <NUM> in any suitable manner. In the illustrated embodiment, the inner portion of the biasing member <NUM> is located in a groove <NUM> in the outer surface of the moveable member <NUM> and the outer portion of the biasing member <NUM> is located in a groove <NUM> in the inner surface of the outer wall of the pressure compensation chamber <NUM>.

The valve assembly <NUM> further comprises a flexible membrane <NUM> which forms a seal against the moveable member <NUM> and the valve body <NUM>. The flexible membrane <NUM> delimits the valve chamber <NUM>, in which the valve element <NUM> is located, from a pressure compensation chamber <NUM>, within which the armature <NUM> is enclosed. The flexible membrane <NUM> may comprise a substantially annular diaphragm extending transversely to the axis <NUM> of the valve assembly <NUM>. The flexible membrane <NUM> may be planar. The flexible membrane <NUM> may be comprised of a resilient material, such as an elastomeric material. The elastomeric material may comprise nitrile-butadiene (NBR) rubber, ethylene propylene diene monomer (EPDM) rubber, fluoroeslastomer (FPM) and/or perfluoroelastomer (FFPM). The flexible membrane <NUM> may be sealed against the moveable member <NUM> and against the valve body <NUM> in any suitable manner. In the illustrated embodiment, the inner edge of the flexible membrane <NUM> is located and retained in an annular groove <NUM> in the outer surface of the moveable member <NUM> and the outer edge of the flexible membrane <NUM> located and retained in an annular groove <NUM> in the inner surface of the valve body <NUM>.

The moveable member <NUM> is connected to the valve body only by the biasing member <NUM> and the flexible membrane <NUM> and is free to move in the axial direction and to rotate about a transverse axis subject to the compliance of the biasing member <NUM> and the flexible membrane <NUM>. In this manner, the moveable member <NUM> effectively floats within the valve body and can oscillate about a transverse axis.

In the illustrated example, the first fluid port <NUM> is defined by an orifice extending through the valve seat <NUM>. The valve seat <NUM> is located within the valve body <NUM> such that a clearance is provided between the outer surface of the valve seat <NUM> and the inner surface of the valve body <NUM>. This clearance defines the second fluid port <NUM>. In this manner, the second fluid port <NUM> is provided by an orifice of the valve body <NUM> extending around the valve seat <NUM>. The valve seat <NUM> may be an integral part of the valve body <NUM> or removable from the valve body <NUM>. The first fluid port <NUM> and the second fluid port <NUM> may be concentric. In the illustrated arrangement, the valve seat <NUM> is located in the valve chamber <NUM> such that the second fluid port <NUM> is fluidly connected to the valve chamber <NUM>. The moveable member <NUM> defines a pressure compensation flow path <NUM> by which the first fluid port <NUM> is fluidly connected to the pressure compensation chamber <NUM>. The biasing member <NUM> may be located in the pressure compensation chamber <NUM>, as shown in <FIG>, or in the valve chamber <NUM>. The flexible membrane <NUM> has a first surface facing towards the valve chamber <NUM> and an opposite second surface facing towards the pressure compensation chamber <NUM>. In this manner, the flexible membrane <NUM> can provide at least one surface on which a pressure from at least one of the first <NUM> and second <NUM> fluid ports can act to provide a pressure compensating force on the moveable member <NUM>.

The actuator assembly <NUM> is positioned against an end of the valve assembly <NUM> and is configured to move the moveable member <NUM> along the axis <NUM> to selectively open and close the valve <NUM>. In this respect, the actuator assembly may comprise an electromagnetic actuator such as a solenoid. In the illustrated arrangement, the actuator assembly <NUM> comprises a solenoid coil <NUM> disposed around a bobbin <NUM> provided within a housing <NUM> of the actuator assembly <NUM>. A fixed core <NUM>, which may comprise a ferromagnetic material, may be provided within a central passage defined by the coil <NUM> and the bobbin <NUM>. The fixed core <NUM> may extend along the axis <NUM> of the valve assembly <NUM>. The actuator assembly <NUM> includes means (not shown) to energise the coil <NUM>, by applying an electrical current thereto. A shim <NUM> may be provided between the valve assembly <NUM> and the actuator assembly <NUM> to limit the stroke of the moveable member <NUM> in the axial direction. The shim <NUM> may be configured as a seal to fluidly isolate the actuator assembly from the valve assembly. In the illustrated embodiment, the shim <NUM> extends transversely across the top of the pressure compensation chamber <NUM> to prevent fluid in the pressure compensation chamber from interacting with the actuator assembly <NUM>. The housing <NUM> of the actuator assembly <NUM> may be integral with the valve body <NUM>. In the illustrated embodiment, the housing <NUM> comprises a downwardly extending annular wall <NUM> by which the actuator assembly <NUM> is connected to the valve assembly <NUM> to form the valve <NUM>, for example by using a threaded connection between an inner surface of the annular wall <NUM> and an outer surface of the valve body <NUM>. The actuator assembly <NUM> may have any suitable shape. In the illustrated arrangement, the housing <NUM> of the actuator assembly is substantially cylindrical and is parallel to the axis <NUM> of the valve assembly <NUM>.

Further detail of the valve will now be described with reference to <FIG> which shows an enlarged view of the valve assembly <NUM>. As discussed above, the moveable member <NUM> defines a pressure compensation flow path <NUM> by which the first fluid port <NUM> is fluidly connected to the pressure compensation chamber <NUM>. The pressure compensation flow path <NUM> comprises a first axial portion <NUM> with a first cross sectional area, or hydraulic diameter, and a second axial portion <NUM> with a second cross sectional area, or hydraulic diameter which is less than the first hydraulic diameter. In the illustrated example, the first axial portion <NUM> is provided by an axial bore in the valve element <NUM> and the second axial portion <NUM> is provided by an axial bore in the shaft portion <NUM>. A third axial portion <NUM> may also be provided, the third axial portion extending at least partially into the armature <NUM>. In the illustrated embodiment, the third axial portion <NUM> is a blind passage. In other embodiments, the third axial portion <NUM> may extend through the full axial extent of the armature <NUM> such that it opens into the pressure compensation chamber <NUM> on the upper surface of the armature <NUM>.

The pressure compensation flow path <NUM> further comprises at least one opening <NUM> extending into the pressure compensation chamber <NUM> at an axial position between the armature <NUM> and the flexible membrane <NUM>. This may be a single opening. The moveable member <NUM> may comprise a plurality of openings <NUM>. The moveable member <NUM> may comprise more than two openings <NUM>, preferably more than three openings <NUM>, most preferably four openings <NUM>. In the illustrated embodiment, the pressure compensation flow path <NUM> comprises four openings <NUM> defined in an outer surface of the moveable member <NUM> and fluidly connected to the first and second axial portions <NUM> and <NUM> by a plurality of transverse bores <NUM> provided in the moveable member <NUM>. The openings <NUM> may be radial openings, that is to say the openings may have an axis perpendicular to the axis <NUM> along which the moveable member <NUM> is actuated. In the illustrated arrangement, the transverse bores <NUM> are perpendicular to the axis <NUM>, but it will be appreciated that other angles could be adopted. For example, one or more of the transverse bores may extend at an angle of approximately <NUM>° to the axis <NUM>.

The openings <NUM> may extend into the pressure compensation chamber <NUM> at a position adjacent to the flexible membrane <NUM>. That is, at a position in which no intermediate components, such as the armature and/or the biasing member, are located between the openings and the flexible membrane <NUM>. The openings <NUM> are positioned at a first axial distance D1 from the flexible membrane, wherein the first axial distance D1 is defined as the minimum axial distance between any part of the openings <NUM> and the flexible membrane <NUM>. Where the biasing member <NUM> is located in the pressure compensation chamber <NUM>, as shown in <FIG>, the biasing member <NUM> is positioned at a second axial distance D2 from the flexible membrane <NUM>, wherein the second axial distance D2 is greater than the first axial distance D1. The first axial distance may be less than <NUM>% of the second axial distance, for example, less than <NUM>%, less than <NUM>%, or less than <NUM>% of the second axial distance. In the illustrated embodiment, the first axial distance is less than <NUM>% of the second axial distance. The height of one or more of the openings <NUM> in the axial direction may be greater than the first axial distance. In examples in which the opening is circular, the height is the diameter of the opening. The height of one or more of the openings <NUM> may be more than twice the first axial distance, for example three times, four times, five times, or ten times greater than the first axial distance.

In the illustrated arrangement, the openings <NUM>, extend into the pressure compensation chamber <NUM> at a position immediately adjacent to the flexible membrane <NUM>.

With reference to <FIG> and <FIG>, the operation of the valve <NUM> will now be discussed in relation to a normally closed valve assembly. In the normally closed configuration, the resilient biasing member is arranged to bias the moveable member <NUM> towards the valve seat, while the actuator assembly is configured to lift the moveable member <NUM> away from the valve seat when the coil is energised. In such a configuration, the valve is closed when the actuator assembly is deactivated. It will be understood that the same valve assembly could be modified to be a normally open valve assembly by arranging the biasing member to bias the moveable member <NUM> away from the valve seat and arranging the actuator assembly to move the moveable member towards the valve seat when energised. In such a configuration, the valve is open when the actuator assembly is off.

When the valve <NUM> is closed, the moveable member <NUM> is biased towards the valve seat by the biasing member <NUM> to seal the valve element <NUM> against the valve seat and thereby prevent fluid communication between the first fluid port <NUM> and the second fluid port <NUM>. The second fluid port <NUM> is in fluid communication with the valve chamber <NUM> such that the fluid pressure in the valve chamber <NUM> is essentially the same as the fluid pressure in the second fluid port <NUM>. The pressure compensation flow path <NUM> fluidly connects the first fluid port <NUM> to the pressure compensation chamber <NUM> to equalise the fluid pressures in the first fluid port <NUM> and the pressure compensation chamber <NUM>. Thus, a pressure difference across the valve seat between the first fluid port <NUM> and the second fluid port <NUM>, is balanced by a pressure difference across the flexible membrane <NUM> between the pressure compensation chamber <NUM> and the valve chamber <NUM>. This can reduce the magnitude of the biasing force required to keep the valve in the closed position and, consequently, reduce the size and energy requirements of the actuator assembly.

Thus, where the fluid pressure in the first fluid port <NUM> is greater than the fluid pressure in the second fluid port <NUM>, the fluid in the first fluid port <NUM> acts to lift the moveable member <NUM> against the force of the biasing member <NUM> by acting against the underside of the valve element <NUM>, and the fluid in the pressure compensation chamber <NUM> acts against the top surface of the flexible membrane <NUM> to push the moveable member <NUM> towards the valve seat. This arrangement provides a pressure compensation force on the moveable member <NUM> such that it can be maintained in a desired position more easily.

To open the valve <NUM>, the coil <NUM> is energised to generate a magnetic field which interacts with the armature <NUM> to pull it towards the actuator assembly <NUM> and thereby move the moveable member <NUM> towards its open position and lift the valve element from the valve seat. In alternative arrangements, the solenoid may instead be configured such that energising the coil <NUM> moves the moveable member <NUM> towards its closed position, or switches the moveable member <NUM> between two or more positions to control the flow of fluid between two or more fluid ports. By varying the power supplied to the solenoid, the moveable member <NUM> may be held in any one of a plurality of positions between a closed position and a fully open position. In the open position, or in a partially open position as shown in <FIG> and <FIG>, the first fluid port <NUM> and the second fluid port <NUM> are in fluid communication across the valve seat along a fluid path <NUM>. Fluid may be communicated through the fluid path <NUM> in either direction, that is to say that fluid may be communicated from the first fluid port <NUM> to the second fluid port <NUM> or from the second fluid port <NUM> to the first fluid port <NUM>, as illustrated by the double-headed arrow in <FIG>. In the example shown, the biasing member <NUM> biases the moveable member <NUM> towards its closed position such that the valve element <NUM> seals against the valve seat <NUM>. This blocks the fluid path <NUM> between the first fluid port <NUM> and the second fluid port <NUM>.

As in the closed position, the first fluid port <NUM> is in fluid communication with the pressure compensation chamber <NUM> through the pressure compensation flow path <NUM> in the moveable member <NUM>, which terminates in the openings <NUM>. By positioning the openings <NUM> of the pressure compensation flow path <NUM> at an axial location between the armature <NUM> and the upper surface of the membrane <NUM>, particularly at a position directly adjacent to the membrane as shown in <FIG> and <FIG>, pressure fluctuations in the first fluid port <NUM> can be almost instantaneously transferred to the upper surface of the flexible membrane <NUM>. This counteracts the tendency for pressure fluctuations to vary the axial position of the moveable member <NUM> and enables the valve opening position to be more accurately controlled.

As shown in <FIG>, at least one component of the valve assembly <NUM> may be comprised of a plurality of discrete components. In this respect, the valve body <NUM> may be provided as a single unitary component. Alternatively, the valve body <NUM> may comprise a first valve body portion 110a and a second valve body portion 110b which are joined together to define the valve body <NUM>. In the illustrated embodiment, the first valve body portion 110a defines the valve chamber <NUM> and the second valve body portion 110b defines the pressure compensation chamber <NUM>. The first 110a and second 110b valve body portions may be substantially cylindrical and sized such that the first valve body portion 110a is concentrically received within the second valve body portion 110b or vice versa. In the illustrated arrangement, the first valve body portion 110a forms an interference fit inside the second valve body portion 110b.

The outer edge of the flexible membrane <NUM> is located and retained in an annular groove in the inner surface of the valve body <NUM>. In the embodiment of <FIG>, the flexible membrane <NUM> is held within a groove defined between the first 110a and second 110b valve body portions. In the arrangement shown, the outer edge of the flexible membrane <NUM> is held between opposite surfaces of the first 110a and second 110b valve body portions. The flexible membrane may be clamped between an upper surface of the first valve body portion 110a and a lower surface of the second valve body portion 110b. A first retaining ring <NUM> may be provided in the valve chamber <NUM> adjacent to the bottom surface of the flexible membrane <NUM>. A second retaining ring <NUM> may be provided adjacent to a top surface of the flexible membrane <NUM>. The flexible membrane <NUM> may be clamped between the first retaining ring <NUM> and the second retaining ring <NUM>, whereby the first and second retaining rings define at least part of the groove between first and second valve body portions. In the arrangement shown, the underside of the first retaining ring <NUM> rests against an upward facing shoulder 119a on the inner surface of the first valve body portion 110a and the upper surface of the second retaining ring <NUM> rests against a downward facing shoulder 119b on the inner surface of the second valve body portion 110b. The first retaining ring <NUM> and the second retaining ring <NUM> are sandwiched together between the shoulders 119a and 119b to secure the retaining rings in place and to exert a clamping force on the flexible membrane <NUM> when the first and second valve body portion 110a and 110b are assembled together to form the valve body <NUM>. Together with the first 110a and second 110b valve body portions, the first <NUM> and second <NUM> retaining rings may be dimensionally tuned so as to control the effective area of the top and bottom surfaces of the flexible membrane <NUM> available for the purposes of pressure compensation. In the embodiments shown in <FIG>, the effective area of the top surface of the flexible membrane exposed to the fluid pressure in the pressure compensation chamber <NUM> is smaller than the effective area of the bottom surface of the flexible membrane exposed to the fluid pressure in the valve chamber <NUM>. This increases the amount of force acting on the bottom surface of the membrane relative to the force acting on the top surface of the membrane for a given fluid pressure. In some embodiments, the effective area of the top surface of the flexible membrane is substantially the same as the effective area of the underside of the valve element such that the hydraulic forces on the top surface of the flexible membrane and on the underside of the valve element cancel each other out.

In embodiments not forming part of the claimed invention, the moveable member <NUM> may be provided as a single unitary component. Alternatively, the moveable member <NUM> may comprise a plurality of discrete components, which may be fixed or fitted together by any suitable means. The valve element <NUM> and the armature <NUM> may be discrete components which are directly connected to each other in the absence of an intermediate shaft portion. The valve element <NUM> and the shaft portion <NUM> may be provided as a unitary component and the armature <NUM> provided as a discrete component which is connected to the shaft portion <NUM>. The armature <NUM> and the shaft portion <NUM> may be provided as a unitary component and the valve element <NUM> provided as a discrete component which is connected to the shaft portion <NUM>.

In the embodiment illustrated in <FIG>, the valve element <NUM>, armature <NUM> and shaft portion <NUM> are provided as three discrete components which are connected together to form the moveable member <NUM>. These components may be fitted together, by an interference fit or otherwise, so as to be retained in fixed relation to one another and constrained to move as a single body during operation of the valve. According to the invention, the shaft portion <NUM> and the valve element <NUM> are discrete components which are fixed together with an interference fit.

The valve element <NUM> may comprise an annular body 121a with an axial bore 121b extending along the axis <NUM> of the valve assembly <NUM> to define the first axial portion <NUM> of the pressure compensation flow path. The transversely extending shoulder <NUM> may comprise a resilient sealing element 121c for engagement with the valve seat <NUM> when the valve is closed. The armature <NUM> may comprise a disc shaped body 122a having a blind bore or cavity 122b disposed therein and extending along the axis <NUM>. The cavity 122b may be surrounded by a downwardly extending annular lip 122c.

Unlike some known arrangements, the armature <NUM> does not extend axially to a position within the coil <NUM>. Due to this arrangement, the moveable member <NUM> is able to rock, or rotate, about a transverse axis such that its longitudinal axis can be misaligned with the valve axis <NUM> without being constrained by any axial extension into the coil <NUM>. Instead, the moveable member <NUM> can rock about a transverse axis to the extent allowed by the stiffness and/or compliance of the flexible membrane <NUM> and the biasing member <NUM>. In this way, when the valve is in its open position and not in contact with the valve seat <NUM> such that its movement is not constrained by the valve seat <NUM>, it will be appreciated that rotation of the moveable member <NUM> about the transverse axis is constrained solely by the biasing member <NUM> and the flexible membrane <NUM>. This therefore provides an additional degree of freedom of movement through which the valve assembly <NUM> can compensate for imbalances of pressure.

The shaft portion <NUM> comprises a first end 123a and a second end 123b. In the example shown, the first end 123a is located at a lower end of the shaft portion <NUM> and is received in the axial bore 121b of the valve element <NUM>, while the second end 123b is located at an upper end of the shaft portion <NUM> and is received and retained in the blind cavity 122b in the underside of the armature <NUM>.

The first end 123a of the shaft portion <NUM> may be substantially cylindrical and comprise an axial bore. The first end 123a is concentrically received in the axial bore 121b of the valve element <NUM> and may be retained via an interference fit. The first end 123a extends along only part of the length of the axial bore 121b of the valve element <NUM>, such that the exposed portion of the axial bore 121b beneath the shaft portion <NUM> defines the first axial portion <NUM> of the pressure compensation flow path <NUM> and the axial bore of the first end 123a defines the second axial portion <NUM> of the pressure compensation flow path <NUM>. The first axial portion <NUM> has a first diameter defined by the diameter of the axial bore 121b of the valve element <NUM>. The second axial portion <NUM> has a second diameter defined by the diameter of the axial bore of the first end 123a of the shaft portion <NUM>, wherein the first diameter is greater than the second diameter.

The second end 123b may be substantially cylindrical and may comprise an axial bore extending along the axis <NUM> to define the third axial portion <NUM> of the pressure compensation fluid path <NUM>. Between the first end 123a and the second end 123b of the shaft portion <NUM> is an intermediate shaft portion in the form of at least one transversely extending shoulder or projection 123c which defines the transverse bores <NUM> of the pressure compensation flow path <NUM>. Such transverse bores may extend in a direction perpendicular to the axis <NUM>. The at least one transverse shoulder or projection 123c has a transverse dimension which is greater than that of the first end 123a and the second end 123b of the shaft portion <NUM>. The at least one transverse shoulder 123c may comprise a single annular shoulder which circumscribes the shaft portion <NUM>. Alternatively, the at least one transverse shoulder 123c may comprise a plurality of transverse shoulders 123c which are spaced apart in the circumferential direction. As the transverse shoulder 123c of the shaft portion <NUM> extends beyond the second end 123b of the shaft portion <NUM> in the transverse direction, the biasing member <NUM> may be clamped between the at least one transverse shoulder 123c and the armature <NUM>, while the flexible membrane <NUM> may be clamped between the at least one transverse shoulder 123c and the valve element <NUM>.

Specifically, the biasing member <NUM> may be retained at an inner portion thereof in a groove defined between a bottom surface of the lip 122c of the armature <NUM> and an upper surface of the transverse shoulder 123c of the shaft portion <NUM>. Therefore, the biasing member <NUM> may be held in fixed relation to the moveable member <NUM> by being clamped between the second end 123b of the shaft portion <NUM> and the armature <NUM>. The second end 123b may extend along only part of the length of the blind cavity 122b such that a gap is provided between a top surface of the second end 123b and the closed end of the blind cavity 122b. This clearance at the second end 123b of the shaft portion <NUM> ensures that the biasing member <NUM> can be securely clamped between the armature <NUM> and the shaft portion <NUM> regardless of the manufacturing tolerances of the second end 123b and the blind cavity 122b. Similarly, the flexible membrane <NUM> may be retained at an inner edge thereof in a groove between the bottom surface of the transverse shoulder 123c of the shaft portion <NUM> and an upper surface of the annular body 121a of the valve element <NUM>. The degree to which the flexible membrane <NUM> is clamped by these components can be tuned during assembly by adjusting the relative axial positions of the valve element <NUM> and the shaft portion <NUM>.

The arrangement shown in <FIG> is particularly advantageous for the assembly of the valve, especially if assembly were to be performed by sequentially inserting components into the bottom end of the valve assembly <NUM>, that is, into the end of the valve assembly in which the fluid ports are located. In this respect, starting from the second valve body portion 110b, which may be fixed to the annular wall <NUM> of the housing <NUM> of the actuator assembly <NUM>, the armature <NUM> can be inserted into the second valve body portion 110b from the bottom end of the valve assembly <NUM>. Subsequently, the biasing member <NUM> can be inserted, followed by the shaft portion <NUM>, wherein the second end 123b of the shaft portion <NUM> can be interference fit with the cavity 122b of the armature <NUM> to thereby retain the inner portion of the biasing member <NUM>. The outer portion of the biasing member <NUM> may be retained in a particular axial position by the groove <NUM> of the second valve body portion 110b. Following this, the second retaining ring <NUM> may be inserted into the bottom end of the valve assembly <NUM> so as to surround the shaft portion <NUM>, and it may be retained in a particular axial position by the downward facing shoulder 119b on the inner surface of the second valve body portion 110b. Then, the valve element <NUM>, with the sealing element 121c, may be inserted into the bottom of the valve assembly <NUM> and interference fit with the first end 123a of the shaft portion <NUM> to thereby hold an inner portion of the flexible membrane <NUM> in a fixed position. Finally, the first retaining ring <NUM> and the first valve body portion 110a can be inserted into the bottom of the valve assembly <NUM> so as to be concentrically received by the second valve body portion 110b and to secure an outer portion of the flexible membrane <NUM> in a fixed position. The valve seat <NUM>, defining the first fluid port <NUM>, may be comprised as an integral part of the first valve body portion 110a or may be a discrete component fixed thereto by an interference fit or any other suitable fixing means.

Referring to <FIG>, a second embodiment of a valve assembly <NUM> is shown. The second embodiment is similar in structure and operation to the first embodiment of the valve assembly discussed above in relation to <FIG> and similar reference numerals are used to denote similar features. In this embodiment, the first axial portion <NUM> and the second axial portion <NUM> of the pressure compensation fluid path <NUM> are connected by a sloped portion <NUM> in which the diameter of the pressure compensation flow path gradually decreases from the first diameter to the second diameter. This is in contrast to the first embodiment, in which there is a step change between the first and second diameters. The sloped portion <NUM> may be provided by a substantially conical surface. Where the moveable member <NUM> is formed from discrete elements, as shown in <FIG>, the sloped portion <NUM> is preferably provided as a sloped end face at the first end of the shaft portion.

An additional optional feature illustrated by <FIG> is related to the armature <NUM>. In addition to the openings <NUM> of the pressure compensation fluid path <NUM> into the pressure compensation chamber <NUM>, the armature <NUM> may comprise one or more transverse armature bores <NUM> which provide additional openings into the pressure compensation chamber <NUM>. The transverse armature bores <NUM> may extend transversely outward from the axis <NUM> to a side surface of the armature <NUM>. Further, instead of having a blind cavity (see <FIG>), the armature <NUM> may comprise a through hole <NUM> which is open to the upper surface of the armature <NUM> to fluidly connect the third axial portion <NUM> with the pressure compensation chamber <NUM>. Therefore, during use, fluid may flow from the first fluid port <NUM>, through the first <NUM> and second <NUM> axial portions of the pressure compensation fluid path <NUM> and then into the pressure compensation chamber <NUM> through the transverse bores <NUM> and openings <NUM>, through the third axial portion <NUM> and the through hole <NUM> and through the transverse armature bores <NUM>. The provision of multiple flow paths can further reduce the time lag between pressure changes in the first fluid port <NUM> and the pressure compensation chamber to further improve valve control.

Claim 1:
A valve assembly (<NUM>) for a valve (<NUM>), comprising:
a valve body (<NUM>) having walls defining a valve chamber (<NUM>);
a first fluid port (<NUM>);
a second fluid port (<NUM>);
a valve seat (<NUM>) located between the first and second fluid ports;
a moveable member (<NUM>) comprising:
a valve element (<NUM>) at its first end,
an armature (<NUM>) at its second end, and
a shaft portion (<NUM>) extending axially between the valve element and the armature,
wherein the moveable member is moveable in an axial direction to bring the valve element into and out of engagement with the valve seat to selectively open and close the valve and wherein the entire moveable member is spaced from the walls of the valve body when the valve is open or partially open;
at least one biasing member (<NUM>) configured to support and bias the moveable member in the axial direction; and
a flexible membrane (<NUM>) which forms a seal against the moveable member and the valve body to divide the valve chamber into a flow chamber in which the valve seat and valve element are located and a pressure compensation chamber (<NUM>) within which the armature is entirely enclosed,
wherein the moveable member comprises one or more bores (121b, <NUM>) defining a pressure compensation flow path (<NUM>) by which the first fluid port is fluidly connected to the pressure compensation chamber, the pressure compensation flow path having at least one opening (<NUM>) extending into the pressure compensation chamber at an axial position between the armature and the flexible membrane,
wherein the pressure compensation flow path comprises:
a first axial portion (<NUM>) with a first length and a first cross-sectional area; and
a second axial portion (<NUM>) adjacent to the first axial portion with a second length and a second cross-sectional area which is less than the first cross-sectional area,
characterised in that the first length is at least <NUM> percent of the second length;
wherein the valve element comprises a first axial bore (121b) and the shaft portion comprises a second axial bore, wherein the first axial portion of the pressure compensation flow path is defined by the first axial bore and the second axial portion of the pressure compensation flow path is defined by the second axial bore, and
wherein the shaft portion (<NUM>) and the valve element (<NUM>) are discrete components which are fixed together with an interference fit.