This invention relates to a fluid valve assembly. The invention is particularly, though not exclusively, applicable to a fluid valve assembly for chemical or biological analysis apparatus.

The control of fluid flow is commonly effected by the use of valves. For example, in instruments for chemical or biological analysis, such as a Coulter Aperture based particle counter, it is often necessary to control the flow of very small volumes of fluid very accurately if the analysis is to be sufficiently accurate.

Such control is not well served by conventional forms of valves. Various considerations may have to be taken into account.

Firstly, the low volume, or dead space, within the valve may be the source of a reading error. The dead space in a valve may retain a significant amount of fluid when it is shut which could later be introduced into the subsequent flow of the fluid, contaminating it. It is also necessary to be able to clean thoroughly such instruments in order to flush out as much of the fluid from a previous analysis as possible . Again, the valve may harbour pockets of the fluid which it is not easy to remove by flushing. This contamination of one sample by a previous one is commonly called carryover.

Secondly, the valve may have a displacing effect on the flow of fluid as it is actuated. This may also have a distorting effect on an analysis by the 'pumping action' which may result.

Diaphragm valves are known. However, they suffer from poor carryover as the diaphragm, being relatively large, allows the fluid to slow down as it flows through the valve in an unpredictable manner. Small viscosity and temperature changes alter the flow pattern.

Pinch valves operate by clamping on a tube to control the flow of fluid. These pinch valves, comprising a flexible tube and a clamp, have substantially zero carryover, but do suffer from other problems. It is found that they tend to stick shut when the clamping is removed after being maintained in a clamping position for a significant length of time. It is possible to reduce this by making the valves normally open so that in any extended period during which the apparatus is standing idle, the tube is not closed. However, using a normally open valve is not convenient in many instrument designs. It has also been proposed to use a pinch valve in which the tubing wall is both clamped and pulled apart to overcome the sticking problem.

Ideally any valve arrangement should substantially maintain the fluid velocity of the connecting tubes, so that the fluid is not allowed to slow down significantly nor get trapped in corners as it flows through the valve.

The fluid displacement problem associated with valves can be illustrated in relation to pinch valves. As the pinch valve is closed it changes the volume of the conduit with which it is associated. In the chemical/biological analysis field this reduction in volume may be around 15 microlitres for a small tube and depends on the tube diameter. A similar change in volume will be experienced when the valve is opened. This may be a sufficient amount to affect results significantly. Diaphragm valves suffer from a tendency to 'pump' fluid by changing volume as they are opened and closed, but by a larger amount depending on the diameter of the flexible member.

According to the present invention there is provided a fluid valve assembly comprising: a valve body at least partially defining a valve chamber, a valve seat therein and inlet and outlet ports communicating with the valve chamber upstream and downstream of the valve seat; and a valve member arranged sealingly to engage with the valve seat; wherein the valve member is mounted relative to the valve body on a resilient support which allows the valve member to move between valve seat engaging and disengaging positions.

In one form of the invention the resilient support has a relatively thin portion which provides a region less resistant to a distorting force which generally defines the manner in which the support will yield to a force applied. Preferably, the resilient support also defines the valve member which may comprise a valve plug for sealing against the valve seat surrounding an aperture in the valve chamber.

The valve member may be located within the part of the chamber defined by the valve body or the valve member may be located within the part of the chamber defined by the support.

The assembly may include a valve actuator extending into a recess in the support to engage the valve member, the actuator being movable to urge the valve member between the engaging and disengaging positions against the resilient force of the support. The actuator may be formed with a reinforcing head which is received in the region of the valve member which engages the valve seat.

Preferably, the valve member is moulded as a unitary structure which is arranged to project into a recess partially defining the valve chamber, which structure closes the chamber.

The valve seat may be formed on a hollow projection extending into the valve chamber, the projection being connected with one of the ports. In this case, the valve seat surrounds an aperture in the hollow projection either as a chamfered end face thereof are formed in the side wall, which valve seat is arranged to engage a generally complementarily orientated sealing valve member surface on the wall of the chamber defined by the support.

The resilient support for the valve member may be arranged so that the valve assembly is normally open or normally closed in the least stressed condition of the resilient support.

In a chemical/biological analyser application the internal diameter of the tubing associated with the valve assembly is typically 1.5mm. The travel of the valve member in relation to the valve seat is very small, of the order of 0.75mm. The invention has a reduced pumping action or tendency to displace fluid when it is actuated. This arises from the diameter of the sealing part of the valve member which is only slightly larger, preferably no more than 25%, than the diameter of the valve seat.

Pumping is calculated from the resilient member diameter and its travel. The resilient port only has to be slightly larger than the inlet pipe diameter to seal properly. 10% is reasonable minimum.

TΓ

Pumping volume = "~ (seat dia + ) x travel For: seat of 1.5mm + 25% for resilient member x 0.75 travel

Pumping = -jf [1.5 + 0.25 (1.5) ] ² x 0.75 = 2.07 mm ³ For: seat of 1.5 + 50% x .75 travel

Pumping = 2.98 While this latter figure is more, it is still less than equivalent pinch valves.

The assembly according to the invention also requires a smaller actuation force than an equivalent pinch valve which requires compression of the tubing itself or a diaphragm arrangement which comprises a larger flexible member that must be actuated against the force derived from the fluid pressure acting on the relatively considerable diaphragm area. The support does not have a large distance to shut off over, nor does it have an excessive area over which the fluid pressure in the valve is exerted.

The present invention can be put into practice in various ways some of which will now be described by way of example with reference to the accompanying drawings in which :-

Figure 1 is a sectional view of a first valve assembly according to the invention;

Figure 2 is a sectional view of a second valve assembly according to the invention; and

Figure 3 is a sectional view of a third valve assembly according to the invention.

Referring to Figure 1, a valve assembly comprises a valve body 10 which is a junction between tubes (not shown) in a chemical or biological analysis instrument. The tubes are respectively connected to inlet and outlet ports 12 and 14 formed in the body 10.

The valve body 10 also defines the valve chamber 16 by which the inner and outlet ports communicate. The chamber 16 comprises a circular recess 18 in the valve body 10 which is co-axial with the inlet port 12. The

valve seat 19 is formed as a tapered portion of the recess which merges the circular recess 18 with the inlet port 12. The outlet port 14 extends perpendicularly and radially with respect to the axis of the recess 18 and is let into the side wall of the body 10 defining the circular recess 18. The circular recess 18 is open at its end opposite the inlet port 12.

A resilient valve member 20 projects into the recess 18 from its open end. The member 20 comprises a recess-engaging portion having a circular flange 22 projecting radially from a circular sleeve 24. The sleeve 24 is of substantially the same diameter as the circular recess 18 into which it is inserted to hold the valve member 20 in position. The extent of projection of the valve member 20 into the recess is determined by the flange 22 engaging the external surface of the valve body 10.

A co-axially projecting circular section hollow stalk 26 projects further into the recess 18 from the sleeve 24. The end of the stalk 26 is formed of the solid, i.e., non-hollow, valve seat engaging portion 28 of the same resilient material.

The thickness of the wall of the hollow stalk is less than the thickness in the region of the sleeve 24 and the flange 22.

The outer surface of the end of the valve seat engaging portion 28 is in the shape of a cone. The included angle of the cone shape is substantially the same as

the degree of taper of the valve seat 19 between the circular recess 18 and the inlet port 12. The cone 28 is spaced from the valve seat 19 by a distance sufficient to allow substantially unimpeded passage of the fluid between the inlet and outlet ports. It will be noted that the outside diameter of the stalk is in the region of 60% of the diameter of the circular section recess 18.

A rigid actuating push rod 30 is received in the conical valve seat engaging portion 28 of the valve member 20. The rod 30 extends along the hollow centre of the stalk 26 to project beyond the axial extent of the flange 22. The end of the rod 30 is formed with a circular section head which has a conical surface nearest the valve seat with a similar degree of taper. The head 32 provides a reinforcement for the resilient valve member 20 in the region of its engagement with the valve seat 19. The included angle of the conical shape head 32 on the push rod 30 is the same as that on the valve seat engaging portion 28.

The spacing of the valve member from the walls defining the recess is chosen to create minimal fluid disturbance in the transition from the inlet port to the outlet port. Where possible the corners in the valve chamber are radiused instead of being sharp in order to avoid providing spaces in which fluid residue could collect and from which it will be difficult to flush.

By depressing the push rod 30 the stalk 26 yields and is stretched, moving the conical valve seat engaging portion 28 towards the valve seat portion 18, restricting the low between the ports 12 and 14. The resilient material of the conical valve seat engaging portion 28 engages the valve seat portion 18 to effect a seal when the push rod 30 is sufficiently depressed. Removing the depressing force from the push rod 30 allows the resilient stalk 26 to retract away from the valve seat portion 18.

The valve assembly is normally open due to the resilience of the stalk. However, it will be appreciated that it could equally well be arranged to be normally closed.

Figure 2 illustrates a second embodiment of the invention. An inlet port 38 is connected to one end of a rigid tube 40 which has an obliquely cut or chamfered free end constituting a valve seat 42, projecting from a main valve body 44. An outlet port 46 is formed in the valve body 44 which extends perpendicularly to the tube 40. The inlet and outlet ports communicate with a valve chamber 48 partially defined in the valve body 44 and enclosed by a hollow resilient stalk 50 which has a closed end, closing the valve chamber. The tube 40 extends inside the chamber 48 defined between the stalk 50 and the valve body 44. The inner surface 53 of the stalk adjacent the valve seat 42 is arranged at a slightly more steeply inclined attitude than the chamfered end of the tube 40, constituting the valve seat 42.

The stalk 50 has an external flange 52 at its base and an annular projecting lip '54. The lip 54 is of the same external diameter as the diameter of the circular recess of the valve body 44. The stalk 50 is clamped in place by means of clamps 56 bearing on the flange 52 to hold it against the valve body 44. The wall thickness of the stalk is least between the closed end and the flange 52.

The valve is actuated by pressing on the stalk 50 in the region of the thicker end portion opposite the inclined surface 53 to regulate the flow from the inlet port 38 through the tube 40. The stalk 50 yields in the thinnest wall region and bends until the attitude of the inclined surface 53 is substantially the same as that of the valve seat 42 when the two are brought into sealingly engagement. Again, this valve assembly could equally well be arranged to be normally closed instead of the illustrated normally open arrangement .

In an alternative form of this embodiment the chamfered end face of the tube 40 could be simply closed and the aperture around which the valve seat would be defined could be formed in a side wall of the tube or even in the closing end of the tube. Clearly the resilient stalk 50 would need to be shaped to complement this change in the position of the valve seat as necessary.

Figure 3 is a modification of the valve in Figure 1 in which like parts have like numerals. The outlet port 14' is parallel to the inlet port 12. To accommodate this the cross-section of the recess is oval although it could be maintained circular but of a larger

diameter. In this regard the resilient stalk is formed with an oval sleeve 24', if necessary, by which it is held in position in the recess 18' .

Suitable materials for the resilient stalk include elastomers chosen for low working fluid contamination and chemical resistance. Silicon rubbers, polyurethane, viton, butyl, natural rubber, kalrez (PTFE rubber) or any other such material will be suitable. The material should not be too hard to prevent the thin walls stretching, nor to soft that the system pressure distorts the entire insert or its thin wall during operation at intended fluid pressures. As the valve assembly is suitable for a wide range of applications, material choice will be tied to the conditions of use.