WO2001090616A1

WO2001090616A1 - Valve sub-assembly

Info

Publication number: WO2001090616A1
Application number: PCT/GB2001/002333
Authority: WO
Inventors: Matthews Dene
Original assignee: Satchwell Control Systems Limited
Priority date: 2000-05-23
Filing date: 2001-05-23
Publication date: 2001-11-29
Also published as: GB0012541D0; CN1386175A; EP1407176A1

Abstract

Valve assemblies are disclosed which include a valve sub-assembly having a flow resistance member (6) which in cooperation with a valve housing (4) provides simultaneously adjustable flow resistance paths for full throughflow and bypass flow paths. The flow resistance member (6) is rotatable in the valve housing (4) to provide this simultaneous adjustment and is maintained in the selected position by an external clip (32) having a groove (34) engageable with an arm (36) of the flow resistance member (4). A flow control member (8) rotatable within the flow resistence member (6) controls fluid flow through the valve assembly (2). The adjustable flow resistance reduces the number of unique items to provide a selection of valve assemblies with different flow resistance. The rotational flow control member (8) provides low torque flow control allowing the use of low torque servo motors (10) yet which can provide highly accurate proportional flow control.

Description

VALVE SUB-ASSEMBLY

The present invention relates to sub-valve assemblies and, in particular, those suitable for controlling flow between a first fluid circuit and a bypass fluid circuit in a valve assembly.

A known application of such a valve assembly is in association with a fan-coil heating/cooling system in which air is blown over a coil through which a heated or cooled fluid flows, the fluid generally being provided at a substantially fixed pressure and temperature. The temperature of coil, and hence the air, is then controlled by selecting how much of the fluid flows through the coil and/or bypass circuit.

A known valve assembly for providing such a selective bypass function has first, second and third fluid feeds, the fluid flow from the first fluid feed (connected to the return side of the coil) to the third fluid feed (connected to a return pipe for returning fluid to a fluid supply) and second fluid feed (connected to an inflow conduit connecting the fluid supply to the coil) to the third fluid feed being simultaneously controlled by a single, linearly movable flow control member. A fluid feed may be formed from a single passageway, conduit or the like or two or more acting in parallel to couple a given source of fluid with some destination for the fluid.

In one arrangement, the third fluid feed is fed from a central chamber with an upper and lower circular valve opening. A flow control member with both upwardly and downwardly tapering sealing elements is movable within the chamber by a linear actuator. The upper valve opening leads from the chamber to the first fluid feed, the lower valve opening from the chamber to the second fluid feed. Such a valve assembly can be conveniently formed as a four-port

assembly with the first and third fluid feeds leading to two of the ports, an inflow conduit connecting the other two-ports, the second fluid feed being coupled to the inflow conduit at some point between the latter two pairs of ports.

When the valve member is pushed to its lowermost position, the upper valve opening is fully open and the lower valve opening fully closed, when at its uppermost position the upper valve opening is fully closed and the lower valve opening fully opened and when at intermediate positions both the lower and upper valve openings are open to a varying degree. When the lower valve opening is fully closed, the bypass is closed and the coil receives the full flow from the fluid supply, when the upper valve is fully closed the coil circuit is fully bypassed, when in the intermediate positions a variable, selectable flow through the coil can be obtained.

The cheapest way to control such a valve is to switch between the fully opened and fully closed bypass condition by means of a wax pill which when energised acts against a return spring. This, however, provides a crude control function and tends to be unreliable in continuous operation.

A more complex but more expensive approach is to use the wax pill to act against the return spring whilst the wax pill condition is controlled by applying a pulse width modulated signal to an internal heating element, the degree of melting of the wax pill determining the position of the valve between 0 and 100%.

A further approach is to use an electronically positioned linear actuator driven by a motor that can be controlled to adopt a desired position of the valve stroke. This provides more accurate proportional control than the wax pill actuator but at the expense of increased costs of the actuator.

A common feature of these prior art valve assemblies, however actuated,

is that they have a linear stroke and the valving element must seat against the fluid pressure when closing the bypass, typically requiring a seating force of

100N. Wax pill actuators also operate with a short linear stroke (about 2mm).

It is known that such valve assemblies should be selected so as to present a desired flow resistance when the bypass circuit is fully closed and the coil circuit fully opened and vice versa, the desired values being dependent on the flow resistance of the coil and associated fluid supply components. One measure of flow resistance is the dimensionless parameter Kv, higher values denoting greater flow for a given pressure drop.

There are several disadvantages associated with such prior art valve assemblies. The need to match the flow resistance characteristics to a particular coil circuit requires several versions of the same valve assembly to be made increasing stock requirement. The linear stroke, particularly when short, means the profile of the valving elements must be very accurately machined, the small gap between the valve and the valve seats are prone to trapping any solids in the fluid. They also require high force output actuators with their associated expense. Wax pill actuators have a very slow response time so all required test cycling of the completed valve assembly is very time consuming

and so costly.

Similar considerations apply to two-port valve assemblies where flow-rate is controlled through the valve assembly between an inlet and an outlet and, ideally, the minimum flow resistance when the valve assembly is in the fully open position is selected for the particular application.

The present invention seeks to provide an improved, versatile valve sub- assembly which can be used in two, three or four-port valve assemblies which address these drawbacks of the prior art devices.

Accordingly, the present invention provides a valve sub-assembly comprising: a flow resistance member having a flow chamber from which extend first, second and third passageways through the body of the first valve member; a flow control member locatable in the flow chamber in sealed relationship to the flow resistance member and having valve elements for selectively adjusting the degree of opening of the first and second passageways; the flow control member and flow resistance member being relatively rotatable so that the valve elements can fully close the first passageway and fully open the second passageway, partially open the first and second passageways, or fully open the first passageway and fully close the second passageway.

As the flow control member and flow resistance member relatively rotate to more open or close the first passageway so it simultaneously, eg proportionately, more closes or opens, respectively, the second passageway.

The valve sub-assembly of the present invention finds particular application in a valve assembly comprising: a valve housing having a housing chamber from which extend first and second fluid feeds; a valve sub-assembly according to the present invention; and the flow resistance member extending into the housing chamber, being sealed to the valve housing, and relatively

positioned in the valve housing in one of two or more possible positions, each position providing a different desired degree of overlap of both the first and second fluid feeds with the respective first and second passageways.

The valve sub-assembly may be used in a valve housing having only two fluid feeds to provide a valve which can control flow from the first fluid feed to the second fluid feed whilst being adjustable to provide a desired flow resistance, from a range of available flow resistances, at the fully open position of the flow control member. It may also be used in valve housing which includes a third fluid feed extending from the housing chamber and is configured as a three-port or four-port valve assembly in which case the overlap of the first and second fluid feeds and first and second passageways provides simultaneous adjustment of the bypass and full flow Kv of the valve assembly so the ratio of Kv values can be automatically maintained at a desired value, eg 10:7 (full flow to bypass values).

As the one design of valve sub-assembly can be used in two, three or four port valve assemblies so reducing stock requirements for such a range of valve assemblies as will be explained below.

The flow control member rotates to control the flow of fluid by closing a given passageway, it does so by a shearing action. This provides that the actuation force required is independent of fluid pressure or induced fluid pressure due to flow. It is therefore now possible to supply valve assemblies which require less energy to move between operating conditions than do prior art valve assemblies which employ linear actuators. For example, the valve assemblies of the present invention can be operated with a torque in the order of 0,3Nm and so are drivable by relatively low cost, readily available, servo motors. For example, model aeroplane control surface actuators can be

employed, with integrated servo control system capable of providing a highly accurate (to 0.1 °) proportional rotary action, relatively inexpensively and compatible with existing controller software designs. Further, there is no need for controller hardware to output high power (non-CPU level) actuating currents,

thus avoiding expense associated with providing high power components to do so, eg triacs, relays, D-A converters, and so on.

The flow resistance member can be configured to fit into the valve housing chamber in a number of positions determined by keying elements, for example. Preferably, the flow resistance rotatable in the valve housing chamber between the two or more possible positions to allow adjustability of the flow resistance after the valve is fully assembled.

The rotational position of the flow resistance member relative to the valve housing may be maintained by a locking member removably mounted on, or engagable with, the valve housing and engagable with a portion of the flow resistance member. The locking member may include slot and the portion of the first member engagable in the slot, for example.

Preferably, the chamber of the valve housing is cylindrical, but other configurations eg conical, can be used. In this arrangement the flow control member may be retained in the valve assembly by a pair of spaced apart pins located in the valve body and engaged at opposite sides of a circumferential groove formed in the outer wall of the flow control member. This also retains the flow resistance member in position in the valve assembly as it is sandwiched between the valve housing and captive flow control member. The pins may pass through a respective pair of apertures formed in the flow resistance member, optionally dimensioned to permit limited rotation of the flow resistance member relative to the valve body to each of the two or more possible positions. The apertures in the flow resistance member may be

dimensioned to allow fluid pressure in the second fluid feed to move the flow resistance member axially towards the flow control member.

The valve assembly may include mounting points for fixing a servo

motor.

The flow control member may include one or more elements, for example arms extending generally perpendicular to the control axis of the flow control member, to also allow manual adjustment of its rotational position relative to the valve housing and accurate setting to known positions, eg fully opened or fully closed, for setting of the servo to the valve or testing, for example.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawing of which:

Figure 1 is an exploded isometric view of a first embodiment of the present invention having a metal valve housing;

Figure 2 is an exploded isometric view of a second embodiment of the present invention having an injection moulded valve housing;

Figures 3 and 4 are isometric views of the embodiments of Figures 1 and 7, respectively, in assembled states;

Figures 5 and 6 are plan views of the valve housings of the embodiments of Figures 1 and 2, respectively;

Figure 7 is a plan view showing the flow restriction member in place in

the valve housing of Figures 2 and 4;

Figure 8 is a plan view of the valve assembly of Figure 2 prior to attachment of the servo motor;

Figures 9 and 10 are upwardly and downwardly directed isometric views of the flow restriction members of the embodiments of Figures 1 and 2;

Figure 1 1 is a cross-sectional plan view of the flow restriction member of Figure 9 along the line XI-XI of Figure 9;

Figure 12 is an isometric view of the flow control member of the embodiments of Figures 1 and 2;

Figures 13 and 14 are isometric front and rear views of the flow restrictor member positions of the embodiments of Figures 1 and 2;

Figure 15 is an isometric view of a further flow restrictor member positioner useful with the embodiments of Figures 1 and 2;

Figure 16 is an isometric view of a variation of the embodiment of Figure 2;

Figure 17 is an isometric view of a portion of Figure 16; and

Figures 1 8 and 19 are cross-sectional views of the valve sub-assembly of Figures 9 and 1 2 as part of two embodiments of two-port valve assemblies.

Referring to Figure 1 , a valve assembly 2 includes a valve housing 4, a flow resistance member 6, a flow control member 8, and a servo motor 10. In this first embodiment the valve housing 4 is metal whereas the flow resistance member 6 and flow control member 8 are injection moulded from a liquid crystal polymer (Vectra (RTM) from Ticona (of the Hoechst group), Milton Keynes to provide very hard wearing, low friction components, with low temperature expansion coefficients.

In the assembled state of the valve assembly of Figure 1 (as shown in Figure 3) the flow restrictor member 6 extends into a cylindrical chamber 12 of the valve housing 4 and is sealed to the valve housing 4 by a pair of spaced apart 0-rings 14 which are seated in circumferential grooves 16 in the outer surface of flow restrictor body 6. Referring now also to Figure 5, the valve housing 4 has extending from the chamber 1 2 a first fluid feed C,, a pair of drilled holes together forming a second fluid feed C₂ and a third fluid feed, C₃.

The flow control member 8 similarly extends into a cylindrical flow chamber 20 within the flow restrictor member 6 and is sealed to it by a pair of spaced apart rings 22 seated in circumferential grooves 24 in the outer surface of the flow control member 8.

The flow restrictor member 6 and flow control member 8 are retained within the valve housing 4 by a pair of pins 26 which pass through respective pairs of through holes 28 to traverse each side of the central axis of the housing chamber 1 2. The pins 26 engage in a circumferential groove 30 in the outer surface of the flow control member 8 above the seal groove 24 so locating it axially in the valve housing 4 whilst permitting limited rotation relative to it. The throughholes pass through raised studs 29 of the valve housing 4.

Each pin 26 also traverses a pair of slots 30 in the flow restrictor member 6 formed above the seal grooves 16. The slots are dimensioned to allow the flow restrictor member about 4 thousandths of an inch of axial movement and circumf erentially to restrict the flow restrictor member to about a 1 2° rotation relative to the valve housing 4, when the pins 26 are in place.

The rotational position of the flow restrictor member 6 relative to the valve housing 4 is fixed by a pair of caps 32 each a push fit ends of the pins 26 (which protrude from the valve housing 4 when in place) each having a slot 34 engagable with a respective outwardly extending arm 36 of the flow restrictor member 6 at the upper side of the flow restrictor member 6. The pair of caps 32 are selected from a number of pairs of caps (not shown) with the grooves 34 positioned to locate the flow restrictor member 6 at different, pre-selected, rotational positions relative to the valve housing 4. As will be explained below, this angle determines the Kv value of the valve assembly, the respective Kv

value being inscribed on the caps 32.

The flow control member 8 includes a pair of outwardly extending arms 38 which indicate to a user its rotational position and has serrated outer ends 40 to aid manual adjustment. Each arm may have a datum which can be aligned with a datum on the valve housing or locking clip to permit accurate setting to fully open, fully closed or mid positions. Referring briefly to Figures 16 and 17, there is shown a valve assembly 200 which is a modified version of the valve assembly 60 of Figure 2, those equivalent parts which have been modified being referenced with the reference numerals of Figure 2 primed. The modifications are to provide the serrated outer end 40' of the extending arms 38' of the flow control member 8' and the clips 32' with respective slots 202 and 204 positioned such that when they are aligned the valve assembly is at the mid position. The slots are about 1 mm wide so a typical credit card can be placed in the slots simultaneously. This provides a quick and reliable method of placing the valve in the mid position prior to attachment of the servo motor which has been set by a controller (not shown) to its 50% setting, even in badly lit circumstances and locations in which the datums are not readily viewed.

A splined cylindrical recess 42 is formed at its upper end for engagement with a drive shaft 44 of the servo motor 10. The servo motor 10 is mounted on the valve housing 4 by four screws 46 which hold a pair flanges 48 which extend outwards from the servo motor 10 (and which may be covered by rubber mounting blocks to reduce vibration and take up tolerances) to a pair of mounts

50 on the valve housing 4. (The screws 46 are not shown in Figure 3) . Snap fittings may be used instead of screws.

The valve housing 4 has four ports; a first port P_{1 f} a second port P₂, a third port P₃ and a fourth port P₄. Their standard connections are that port P.,

couples to the return pipe to the fluid supply system, port P₂ couples to the exit end of a coil (not shown), port P₃ couples to the input end of the coil (not shown) and port P₄ to the input pipe of fluid supply system.

Referring now to Figure 5, the floor of the chamber 12 of the valve housing 4 has a pair of oblate hemispherical recesses 80 in fluid communication with respective twin drilled apertures 82 which form the end of the second fluid feed and through which fluid can enter the chamber 1 2 if open. The recesses 80 are separated by sealing lands 83.

Referring now to Figures 9 to 10, in particular, the flow resistance member 6 has a floor 88 at the bottom of the cylindrical recess 20 in which are formed a pair of apertures 90 which overlap the recesses 80 in the valve housing 4 to a degree dependent on their relative rotational position. In a first relative position the apertures 90 are fully open. As can be seen with reference to Figure 7, the flow resistance member 6 rotates relative to the valve housing 4 the apertures 90 are closed down by the lands 83 as one side of each moves off the recess 80 thus offering an increasing flow resistance to any fluid passing from the second fluid feed into the body of the flow resistance member 6 until if reaches its limit of rotation, determined by the circumferential dimensions of the slots 30, as previously described. In this example there is 12° of rotation movement possible. The lands 83 need not form a tight seal to the flow resistance member as there is no requirement to provide for absolutely no flow through the bypass

circuit. Thus the flow resistance member 8 can be designed to be displaced upwards under fluid pressure into sealing contact with the flow control member 6 with any slight leakage between the lands 83 and the flow resistance member being negligible and of no operational consequence.

A pointer 91 is present (see Figure 10) to avoid assembly errors by providing a keying action with the valve housing 4, 64 and indicating the fluid flow outlet direction when connected to a fluid supply system.

The extension arms 36 have outer flanges which provide a snap-fit to the clips 32.

A keying stud 93 is provided which engages in a part circumferential slot 95 in the flow control member 8 (see Figure 12) to ensure correct assembly.

The flow resistance member 6 has two diametrically opposed radial throughholes 92 and 94 which overlap the fluid feeds leading to the chamber 12 from second and first ports P₂ and P_u respectively. The throughhole 92 is dimensioned to determine the minimum flow resistance offered by the valve assembly 2 when fully open to fluid flow returning from a coil via second port P₂. As the flow resistance member 6 rotates in the valve housing 4 the area of overlap of the port P₂ and first fluid feed reduces so increasing the above described minimum flow resistance. The throughhole 94 is outwardly flared in the horizontal plane so the flow resistance from the chamber 12 to the third f iuid feed leading to first port P., is constant whatever the rotational position of the flow resistance member 6 in the valve housing 4.

The recesses 80, apertures 90 and throughhole 92 are dimensioned so that the ratio of the minimum flow resistances (in Kv) into the chamber 12 from the first port P-, and the third fluid feed is kept substantially constant as the flow resistance member 6 is rotated in the valve housing 4. In this case the ratio is

about 10:7.

In this embodiment the Kv provided by the throughhole 92 can be adjusted from 1 .2Kv to 2.5Kv over a 1 2° rotation of the flow resistance member 6; the minimum Kv of the flow path into the chamber 12 from the second fluid feed being adjusted automatically to be about 70% of this value. Other ratios could be chosen but 70% is a widespread industry standard design figure for a bypass circuit and so chosen for this embodiment.

Referring now to Figure 12, the flow control member 8 is shown in more detail. Extending from the main body portion 100 is a first valving element 102 which covers or leaves open the apertures 90 in the flow resistance member 6 depending on their relative rotational positions. The first valving element 102 is supported by a rod 104 and a part-cylindrical side wall 106 which is a second valving element for opening and closing throughhole 92 of the flow resistance element 8, again dependent on their relative rotational position. The first and second valving elements 102, 106 are arranged so that throughhole 92 is fully opened when apertures 90 are fully closed and vice-versa and profiled at edge 93 to aid smooth flow out of the flow control member 8.

The first valving element 102 has one sector formed with a recess 109 to avoid thick plastics sections. The second valving element 106 has a generally semicircular edge 108 with a central small radius semicircular cut-out 1 10. This cut-out provides linear opening of the throughhole 92 of the flow resistance member 6 so there is a closer approximation to linearity between the servo drive shaft angular position and temperature of the air exiting the fan-coil apparatus. Without this cut-away the rate of change of overlap area of the first fluid feed and first passageway 92 could be too abrupt at the near closed

position, whether opening or closing, to be compatible with thermal characteristics of the controlled heating/cooling system.

The floor of the circumferential groove 30 has a pair of raised portions 31 (only one shown) which co-operate with the pins 26 to limit the rotation of the flow control member to 90° relative to the valve housing 4 or 64.

Figures 1 3 and 14 show front and rear views of the clip 32 with the groove 34 positioned so the valve presents a minimum 1 .2Kv resistance to a coil when in full flow setting. Inner cylindrical recesses 120 are dimensioned to provide a push-fit fitting on the pins 26 with outer cylindrical recesses 1 21 dimensioned to be a push-fit on studs 29 of the valve housing 4 or 64. Wings 123 to either side of groove 34 slot between the valve housing 4 and flow resistance member 8 on assembly.

Figure 1 5 is a further clip 122 and is as the clip 32 of Figure 13 but with a groove 1 24 positioned to set the valve assembly to the 2.5Kv minimum flow resistance rather than 1 .2Kv. Further clips can be provided (not shown) to set the minimum available flow resistance member to intermediate Kv values.

In a second embodiment 60 of the present invention, shown in exploded and assembled conditions in Figures 2 and 4, all components are as in the embodiment of Figures 1 and 3 except the valve housing 64, with the same elements given common reference numerals.

Referring now to Figure 6, there is shown the valve housing 64 of the valve assembly 60 of Figures 2 and 4, which has been formed by injection moulding of a hard polymer, eg Fortron (RTM) Ticona (of the Hoechst group),

Milton Keynes used to form the flow resistance member 6 and flow control member 8. In this case a pair of vertically oriented fins 140 extend downwards

from the bottom of a valve housing chamber 142 to provide the required variable flow resistance through apertures 90 of flow resistance member 6.

The apertures 90 are symmetrically disposed to provide relatively even flow from the second fluid feed C₂ into the chamber 142.

Figure 7 shows a partly assembled valve assembly 60 with the fluid resistance member 6 in place in the valve housing 64 and positioned so the fins 140 partially obscure the apertures 90. The obstruction caused by the fins 140 reduces as the flow resistance member is rotated to its lowest Kv setting (shown in Figure 7). Operationally, it acts identically to the first embodiment.

Figure 8 shows the arrangement of Figure 7 in which the flow control member 8 has been inserted and clips 32 have been mounted on the valve housing 64 to retain the arms 6 of the flow resistance element in the desired Kv setting.

The servo motor 10 in each of the above described embodiments is a type 507 servo motor manufactured by JR, Japan. The servo motor includes all the controls required to position the drive shaft 44 to a desired rotational position with an accuracy of about 0.1° in response to a corresponding 4 to 6V pulse width modulated input signal.

Lower cost controllers can be employed to provide the control signals as power output stages, eg using triacs and relays, are not required.

The ports P-, to P of the valve housing 64 of valve assembly 60 are provided with standard snap-fit mountings 198 for quick attachment to pipes 200 with complementary fittings as shown in Figure 4.

The valve assemblies of the Figures are used as follows.

A valve assembly with Kv settings spanning the required minimum Kv of

the return flow path (port P-^ to port P₂) is chosen. The appropriate clips for this Kv setting are selected and clipped onto the pins 26 to hold the flow resistance member at the corresponding position. The valve assembly is connected to the supply pipes of the coil of the fan-coil apparatus and to the heated or

refrigerated liquid supply and return lines.

A controller (not shown) controls the rotational position of the flow control member 8 to adjust the flow of the liquid through the coil and bypass in response to a heating/cooling demand required by the controller, in dependence on a sensed temperature in the space to be heated or cooled.

Referring now to Figure 1 8, a two-port valve 300 has a valve sub- assembly 302 (as previously described with reference to Figures 9 and 1 2, in particular) sealed to a cylindrical recess 304 of a valve housing 305 by o-ring seal 306. A first fluid feed 308 and a second fluid feed 310 extend from the recess 304.

As in the previously described embodiments, the minium flow resistance is set by setting the rotational position of the flow resistance member 6 to obtain the desired degree occlusion of the fluid feed 310. Thereafter, the flow through the valve is controlled by rotating the flow control member 8 relative to the valve housing 305 and flow resistance member 6.

The apertures 90 of the flow resistance member 8 are blocked off by the bottom wall of the recess 304 and play no part in the operation of this embodiment. Referring to Figure 19, a further embodiment of a two-port valve is

similar to that of Figure 10 but the valve sub-assembly 402 is set in an angled recess 404 in a valve housing 405 such that a first fluid feed 408 is in fluid

communication with passageway 94 of the flow resistance member 6 (see Figure 1 1 ), the minimum Kv resistance of the valve assembly being determined

by the rotational position of the flow resistance member 6 in the recess relative to fins 409 as explained for the four-port valve assembly particularly with reference to Figure 6. The flow through the valve is then controlled by adjusting the rotational position of the fluid control member 8 as in the other described embodiments, the passageway 408 always being fully open.

It will be appreciated the various fixing, positioning, actuating and control arrangements described in relation to the embodiments of Figures 1 to 17 can be readily adapted for use with the two-port valve assemblies of Figures 18 and 19 to provide the same functionality.

It will also be appreciated that three-port valve assemblies based on the above described four-port valve assemblies can be obtained by providing that the second fluid feed is in fluid communication with a single port of the housing rather than a conduit connecting the two-ports of the illustrated four-port valve assemblies.

Claims

1 . A valve sub-assembly comprising: a flow resistance member having a flow chamber from which extend first, second and third passageways through the body of the first valve member, a flow control member locatable in the flow chamber in sealed relationship to the flow resistance member and having valve elements for selectively adjusting the degree of opening of the first and second passageways; the flow control member and flow resistance member being relatively rotatable so that the valve elements can fully close the first passageway and fully open the second passageway, partially open the first and second passageways, or fully open the first passageway and fully close the second passageway.

2. A valve assembly comprising: a valve housing having a housing chamber from which extend first and second fluid feeds; a valve sub-assembly as claimed in claim 1 ; and the flow resistance member extending into the housing chamber, being sealed to the valve housing, and relatively positioned in the valve housing in one of two or more possible positions, each position providing a different desired degree of overlap of both the first and second fluid feeds with the respective first and second passageways.

3. A valve assembly as claimed in claim 2, in which the flow resistance member is rotatable while in the valve housing chamber between the two or more possible positions.

4. A valve assembly as claimed in claim 3, in which the rotational position of the flow resistance member relative to the valve housing is maintained by a locking member removably mounted on the valve housing and engaged with the

a portion of flow resistance member.

5. A valve assembly as claimed in claim 4, in which the locking member includes a slot and the portion of the first member is engagable in the slot.

6. A valve assembly as claimed in claim 2 in which the valve housing includes a third fluid feed extending from the housing chamber.

7. A valve assembly as claimed in claim 6, in which the housing chamber of the valve housing is cylindrical and has an opening at one axial end for

receiving the flow resistance member, the second fluid feed extending from the axial end of the chamber opposite the opening and the first and third fluid feeds extending from opposite sides of the chamber intermediate the axial ends of the chamber.

8. A valve assembly as claimed in any one of claims 1 to 7, in which the flow control member is retained in the valve assembly by a pair of spaced apart pins located in the valve body and lying within opposite sides of a circumferential groove formed in the outer wall of the flow control member.

9. A valve assembly as claimed in claim 8, in which each pin passes through a respective pair of apertures formed in the flow resistance member, the apertures being dimensioned to permit rotation of the flow resistance

member relative to the valve housing.

10. A valve assembly as claimed in claim 9, in which the apertures are dimensioned to allow fluid pressure in the second fluid feed to urge the first valve member axially into contact with the flow control member.

1 1 . A valve assembly as claimed in any one of claims 6 to 9 in the form of a four-port valve housing, the first port being in fluid communication with the third fluid feed, the second port being in fluid communication with the first fluid feed and the second fluid feed being in fluid communication with both the third port and the fourth port.

12. A kit of parts including a valve assembly as claimed in any one of claims 2 to 1 1 and a sufficient number of locking members for selectively positioning the flow resistance member at two or more rotational positions relative to the valve housing.

13. A valve assembly as claimed in any one of claims 2 to 1 2, and including a drive assembly mounted on the valve housing and a rotatable drive shaft coupled to the flow control member.

14. A valve assembly as claimed in any one of claims 2 to 1 3, in which the

rotational position of flow control member relative to the valve housing is manually adjustable.

15. A valve assembly as claimed in claim 14, the locking member and flow control member each having a slot located so as to be aligned with each other when the flow control member is positioned to half open the first and second passageways.

16. A valve assembly substantially as hereinbefore described or as described with reference to Figures 1 , 3, 5 and 9 to 1 5; Figures 2, 4 and 6 to 1 5; or Figures 16 and 17; or Figures 1 8 and 19 of the accompanying drawings.