GB2490180A

GB2490180A - Pump with actively driven valves

Info

Publication number: GB2490180A
Application number: GB1109776.3A
Authority: GB
Inventors: Ian Owen; Eckhard Bez
Original assignee: Hyperspin Ltd
Current assignee: Hyperspin Ltd
Priority date: 2011-04-18
Filing date: 2011-06-10
Publication date: 2012-10-24
Anticipated expiration: 2031-06-10
Also published as: EP2699800B1; EP2699800A4; US20140134003A1; GB201109776D0; GB2490180B; EP2699800A2; WO2012145395A3; WO2012145395A2

Abstract

A fluid, e.g. dry vacuum, pump comprises an inlet 891 and outlet 895 and a cylinder 802 defining an internal volume. A compression member 810 e.g. a piston or diaphragm moves within the cylinder and a valve means 841H, 835H is driven by actuators subject to a controller. The valves selectively allow fluid either to be drawn from the fluid inlet and into the cylinder or expelled by the translation of at least a portion of the compression member. The valves may be respective single inlet and outlet poppet type valves opening directly to the cylinder (Fig. 2) or may comprise an auxiliary valve 841H with either separate inlet and outlet valves (Fig. 4) or a shuttle or slide valve 835H. The valve actuators and piston or diaphragm drivers may be piezo, electromagnetic or solenoid elements. The piston may be coupled to its drive by a coupling allowing axial float.

Description

VALVE ASSEMBLY AND METHOD OF PUMPING A FLUID

FIELD OF THE INVENTION

The present invention relates to valves for pump apparatus. In particular the invention relates to inlet and outlet valves for reciprocating pump apparatus.

BACKGROUND OF THE 1NVENT1ON

Pumping of fluids such as gases, vapours, liquids, slurries and the like is a requirement in a wide range of industrial, domestic and laboratory environments. The fluid may be or comprise a gas, a vapour or a liquid. To accomplish pumping it is known to provide a fluid pump employing a piston arranged to reciprocate back and forth within a pump chamber.

As the piston moves in one direction fluid is drawn into the pump chamber through an inlet valve. As the piston moves in the opposite direction fluid is forced out of the chamber through an outlet valve. Lubricant is typically provided between the piston and a wall of the pump chamber.

The lubricant may have one or more of a number of effects. For example, lubricant typically reduces friction between the piston and pump chamber wall, thereby reducing wear and an amount of heating of the piston and chamber wall. Reducing wear has the advantage that a mechanical life of the pump is extended. The lubricant may also act as a sealing agent.

In certain applications it is undesirable to use lubricant. In some cases this is because the lubricant may cause contamination of the fluid being pumped and/or react with the fluid being pumped. In the case of vacuum pumps, the use of lubricant may be undesirable due to a risk that lubricant or volatile molecules emanating from the lubricant may be introduced into the apparatus from which fluid is being pumped. This can occur for example due to reverse flow of fluid such as a vapour from the pump chamber through the inlet valve, a phenomenon known as backstreaming.

It is therefore known to provide lubricant-free pumps, such as dry pumps, for pumping fluids.

FIG. 1 shows a known fluid pump 1 (which may also be referred to as a compressor) that is particularly suited to use as a vacuum pump under lubricant-free conditions (i.e. as a dry' pump). The pump has a cylinder 2 within which a piston 10 is arranged to be slidable.

The piston 10 is coupled to a coupling rod 12 which is in turn coupled to a crankshaft 11. As the crankshaft 11 rotates the coupling rod 12 causes the piston 10 to move in a reciprocal manner to and fro within the cylinder 2.

The cylinder 2 has a front end 2A at which an outlet valve is provided. The outlet valve comprises a valve disc 31 and a valve seat 2A, the valve seat 2A being provided by the front end 2A of the cylinder 2.

The valve disc 31 is displaceable between a seated condition in which the valve disc 31 abuts the valve seat 2A forming a gas tight seal therewith, and an open condition in which gas is allowed to pass between the valve seat 2A and the disc 31 out from the cylinder 2.

Thus the outlet valve may assume a closed condition or an open condition.

The cylinder 2 in combination with the valve disc 31 and piston 10 defines a pump chamber' through which fluid is pumped.

As the piston 10 executes reciprocal movement within the cylinder 2, the piston 10 alternately moves from a top dead centre (TDC) position in which a front surface lOS of the cylinder 2 is at its most forward position (at or near the front end 2A of the cylinder 2) and a bottom dead centre (BDC) position in which the front surface 105 is at its most rearward position, away from the front end 2A and towards a rear end 2B of the cylinder.

With the piston 10 at the BDC position, inlet apertures 94 formed in a wall of the cylinder 2 are exposed to an internal volume of the cylinder between the piston 10 and the valve disc 31 allowing gas that is to be pumped to flow into the cylinder 2.

The piston is then moved back towards the TDC position, this movement being referred to as an exhaust stroke of the piston. During the exhaust stroke gas in the cylinder 2 is compressed. If the gas reaches a sufficient pressure before the piston 10 reaches the TDC position, the valve disc 31 is displaced from its seated condition allowing the gas to exhaust from the cylinder 2 around a periphery of the valve disc 31.

If the gas does not reach a sufficient pressure before the piston 10 reaches the TDC position, the piston 10 is arranged to abut the valve disc 31 and to force the valve disc 31 away from its seated position thereby to open the outlet valve 30A and exhaust the compressed gas.

It is understood that the provision of an outlet valve in the form of a valve disc 31 having a diameter substantially equal to or greater than a diameter of the cylinder 2 has the advantage that a pump having an increased compression ratio may be obtained compared with other known pumps. This is due at least in part to the provision of an outlet valve having a head having a diameter similar to that of the cylinder 2.

Furthermore, with such a design the piston 10 is able to abut the valve disc 31 and to force open the valve disc 31 to exhaust the gas even when the gas pressure alone is insufficient to open the outlet valve 30A. This has the advantage that lower ultimate pressures may be obtained in a recipient being pumped by the pump.

EF0922166 describes a piston-driven vacuum pump having similar features to that described above.

STATEMENT OF THE INVENTION

Embodiments of the invention may be understood with reference to the appended claims.

In one aspect of the invention there is provided fluid pump apparatus comprising: a fluid inlet and a fluid outlet; at least one cylinder member having an internal wall defining an internal volume thereof; a compression member provided within the internal volume of the cylinder member; and valve means arranged to be actuated by actuator means under the control of control means, the valve means being operable selectively to allow fluid either to be drawn from the fluid inlet and into the cylinder member by translating at least a portion of the compression member in a first direction or to be exhausted from the cylinder member through the fluid outlet by translating said at least a portion of the compression member in a second direction opposite the first.

Embodiments of the invention have the advantage over known fiuid pump apparatus that because actuator means under the control of a control means is provided, the valve means may be opened and closed independently of a pressure difference across the valve means.

In contrast, valve means not having actuator means under the control of control means relies on a difference in pressure across the valve means to open the valve means. Typically a closure member of the valve is biased to a closed position by a spring.

If an opening force on the closure member is sufficient to overcome the bias of the spring, the closure member moves away from the closed position and the valve assumes an open condition.

The use of such valves in known pump apparatus has the disadvantage that the compression member (in the form of a piston in known apparatus) must move a sufficient distance within the cylinder member to create a pressure difference across the valve sufficient to force the valve to open. ln some applications such as vacuum pump applications the pressure required to open the inlet and outlet valves requires a not inconsiderable force to be applied to the piston. This leads to a requirement that a piston drive of not inconsiderable size and weight must be used, such a drive typically having a relatively large power requirement.

Embodiments of the present invention allow a number of improvements over known pump apparatus to be made. For example in some embodiments the pump is smaller, lighter and of lower power consumption than some known pump apparatus.

This is at least in part because when the compression member completes an exhaust stroke over which fluid is expelled from the cylinder member and then begins an intake stroke to draw fluid into the cylinder member, the valve means may be actuated to allow fluid to be drawn through the fluid inlet independently of a difference in pressure across the valve means between the fluid inlet and the internal volume of the cylinder member.

It is to be understood that the valve means may be actuated to allow fluid to be drawn into the cylinder member even when there is substantially no pressure difference between the fluid inlet and the internal volume of the cylinder member.

It is to be understood that the internal volume of the cylinder member occupied by fluid that is drawn into the cylinder member through the valve means may also be referred to as the pump chamber'.

It is to be understood that the term compression member includes a member the whole of which is translated within the cylinder member such as a piston and a member of which only a portion is translated within the cylinder member.

A member only a portion of which is translated within the cylinder member includes for example a member that is caused to deform, deflect or otherwise change shape or form in order to compress fluid within the cylinder member. Thus a membrane or like component that is fixed to a portion of the apparatus such as the cylinder member and caused to deform thereby to change the size of the pump chamber is included by the term compression member.

It is to be understood that the cylinder member may define a volume of circular cross-section (i.e. a cylindrical cross-section) or any other cross-section. For example, a square cross-section, a rectangular cross-section or an elliptical cross-section. Other shapes are also useful.

It is to be understood that as the at least a portion of the compression member moves away from its forward-most position, being also a position of smallest pump chamber volume (known as a top dead centre' (TDC) position) at the start of a suction cycle, fluid may be drawn into the pump chamber through the valve assembly. This has the feature that a head vacuum' that is otherwise created as the compression member so moves may be relieved. It is to be understood that the force required to move the compression member may be considerable when high differential pressures exist across the compression member.

By way of example, in the case of some known vacuum pumps, when the piston member moves away from the TDC position a pressure in the pump chamber may be reduced by up to at least 1 bar below a pressure outside the pump chamber. For a piston 55mm in diameter, an instantaneous torque of around 7-8Nm may be required in order to move the piston from the TDC position towards a bottom dead centre (BDC) position.

Such a torque is too high for certain drive means that it is desirable to use with fluid pumps.

Accordingly, embodiments of the invention have the advantage that drive means of reduced power (and therefore size) may be employed! For example, embodiments of the invention are suitable for use with linear drive assemblies such as magnetic linear drive assemblies.

The inlet vaive may also be referred to as a torque relief valve' since in some embodiments it enables a reduction in an amount of torque that is required to be developed by a motor driving the reciprocating member to and fro within the pump chamber.

For example, in the case that a rotary electric motor is used to drive the piston, the torque that must be developed by the motor to drive the piston may be reduced.

In the case of the example cited above with a piston having a diameter of 55mm, the inlet valve may have a diameter of around 10-15mm in order to reduce the torque to a sufficiently low value in some embodiments.

The apparatus may comprise an inlet valve through which fluid may be drawn into the cylinder member from the fluid inlet and an outlet valve through which fluid may be expelled from the cylinder member to the fluid outlet, each valve having a closure member operable to open or close the valve thereby to allow or prevent flow of fluid therethrough.

Advantageously at least one of the inlet and outlet valves are actuated by the actuator means.

Further advantageously both the inlet valve and the outlet valve are actuated by the actuator means.

Advantageously the inlet and outlet valves are provided with respective different closure elements.

Optionally the inlet and outlet valves share a common closure element, the closure element being operable by the actuator means to move between a first position in which the inlet valve is open and the outlet valve is closed and a second position in which the inlet valve is closed and the outlet valve is open.

The inlet and outlet valves may be provided by a shuttle valve assembly, the common closure element corresponding to the shuttle of a conventional shuttle valve.

The valve means may further comprise an auxiliary valve, the auxiliary valve being provided in a flow-path of fluid between the inlet and outlet valves and the cylinder member such that fluid flowing into or out from the cylinder member flows through the auxiliary valve, the auxiliary valve being operable by the actuator means to prevent a flow of fluid into or out from the cylinder member.

Thus it is to be understood that the auxiliary valve is operable to place the inlet and outlet valves in fluid isolation from the cylinder member or in fluid communication with the cylinder member.

This feature has the advantage that an amount of dead space or dead volume within the cylinder member associated with the valve means may be further reduced.

It is to be understood that by dead space is meant the volume of the cylinder member between the valve assembly and the compression member that is not swept by the compression member.

A reduced size of dead space enhances a pumping efficiency of a pump apparatus. It also reduce a length of time a fluid spends within the cylinder member. This can be advantageous in a number of applications. For example, in the case of intermittent flow through the apparatus of a corrosive fluid, a reduced dwell time' within the cylinder member can reduce an amount of corrosion of the pump due to the corrosive fluid.

In some applications, pumping may be required of a fluid having a finite lifetime and/or a fluid having a finite lifetime in a particular state. An example of such a fluid is a hyperpolarised gas such as hyperpolarised helium-3 or any other suitable hyperpolarised gas.

A hyperpolarised gas typically loses its magnetic polarisation over time. A reduction in the amount of time the gas is present within the apparatus may therefore be desirable in some applications, e.g. where hyperpolarised gas is being pumped into a chamber for the performance of an experiment.

The actuator means may comprise at least one drive unit.

The actuator means may comprise a first drive unit operable to open and close the inlet valve and a second drive unit operable to open and close the outlet valve.

It is to be understood that in some arrangements where a plurality of inlet valves and/or a plurality of outlet valves are provided, a corresponding plurality of drive units may be provided, one for each one of the plurality of inlet and/or outlet valves.

In some arrangements the inlet and outlet valves may be actuated by a single drive unit.

In some arrangements a plurality of inlet and/or outlet valves may be provided. Where a plurality of inlet or outlet valves are provided the plurality of valves may be actuated by a single actuator.

The actuator means may comprise a drive unit operable to open and close the auxiliary valve.

The drive unit may comprise a piezo-electric drive.

It is to be understood that by the term piezo-drive is meant a drive comprising a piezoelectric material and operable to cause axial translation of the valve by application of a suitable electric field to the piezo-electric material. The piezo-drive may be operable according to a slip-stick method of operation or any other suitable method. Slip-stick methods are described for example in US2010314970. For example, the piezo-drive may be operable according to a travelling wave mode such as that described in US5596241, a standing wave as described in U55453653 and US2003052573 or any other suitable method.

The content of US2010314970, U55596241, US5453653 and U52003052573 is hereby incorporated by reference.

Alternatively or in addition the drive unit may comprise an electromagnetic drive.

By providing a valve assembly according to embodiments of the invention the size of a linear drive means capable of driving the compression member may be reduced to a size compatible with a number of important applications. Thus, the possibility of employing linear drive means in a greater range of applications is facilitated by embodiments of the present invention.

Examples of the type of drive means that may be suitable for use in some embodiments of the invention include QDrive STAR (TM) motors produced by CFIC Inc of Troy, New York.

The motors employ an electromagnetic actuator to drive a drive member in the form of a rod member in an axial direction parallel to a longitudinal axis of the rod member.

Suitabie drive means for certain embodiments may be arranged to have a drive member of relatively short stroke, such as a stroke of up to around 10mm, or in the range from around to around 20mm.

In some embodiments of the invention it is desirable to provide the pumping apparatus, including the drive means, within a fluid-tight casing.

Because an entire pump apparatus may be provided in a fluid-tight casing, including the drive means, a requirement to provide seals between the casing and moving components passing through the casing (such as a coupling rod) may be avoided. A coupling rod may be required to pass through the casing in a situation where the drive means is too large to be S provided within the stationary pump casing and has instead to be provided external to the casing.

This has the advantage that leakage of fluid (such as air) into the pump apparatus from an external environment by means of the seals may be reduced or eliminated. Similarly, leakage of pumped fluid out from the pump apparatus to the external environment by means of the seals may also be reduced or eliminated.

In some embodiments in which a magnetic linear drive is employed having an electromagnet, a coupling rod of the compression member may be supported in a magnetic field of the electromagnet by flexure supports. The electromagnet may be provided close to or in thermal contact with an outer wall of the pump apparatus in order to allow efficient conduction of heat away from the electromagnet in use.

It is to be further understood that it is desirable to maintain a relatively small clearance between the piston 110 and the sidewall 102 of the pump chamber 101 in order to allow for expansion of the piston 110 and sidewall 102 in use. The actual value of the clearance will in practice depend upon a size of the components, the materials from which they are to be made, and anticipated working temperatures of the components. It is to be understood that it is desirable to make the clearance as small as possible to reduce leakage of fluid there past.

The drive unit may comprise an electric motor.

The valve means may be provided in a head portion of the apparatus facing the compression member.

Advantageously the apparatus comprises sensor means for sensing a position of the compression member, the control means being arranged to control the actuator means responsive to the position of the compression member.

Optionally the sensor means comprises at least one selected from amongst an optical sensor, a magnetic sensor, an acoustic transducer and an electromagnetic radiation sensor.

Advantageously the apparatus is arranged to sense a position of the sensor by detection of a signal generated by a transmitter and received by a receiver following reflection from the compression member, the signal being one selected from amongst an optical signal, an acoustic signal and an electromagnetic signal.

The apparatus may be arranged to sense the position of the sensor by reference to an amount of a Doppler shift between the transmitted and received signals.

The apparatus may comprise sensor means for sensing a pressure of fluid in the cylinder member, the control means being arranged to control the actuator means responsive to the pressure of fluid in the cylinder member.

Advantageously at least a portion of the compression member is arranged to reciprocate between a first position proximate the valve means and a second position distal the valve means.

Further advantageously the control means is operable to control the valve means to allow a flow of fluid into the cylinder member from the fluid inlet when the at least a portion of the compression member moves from the first position towards the second position thereby to reduce a magnitude of a force required to so move the compression member.

It is to be understood that the valve means may be controlled to allow fluid into the cylinder member from the fluid inlet at any suitable position of the at least a portion of the compression member at or between the first and second positions. However advantageously the valve means allows fluid to flow into the cylinder member when the at least a portion of the compression member moves from the first position to the second position before said at least a portion reaches the second position thereby to relieve the vacuum otherwise created as the compression member so moves.

It is to be understood that because the inlet valve is controlled by the actuator means, the inlet valve can be opened when the at least a portion of the compression member is substantially at the first position.

As described above, in known arrangements the inlet valve cannot be opened until the at least a portion of the compression member has moved a sufficient distance from the first position to allow a pressure difference across the inlet valve to exceed the force required to open the inlet valve. This force may be provided by a spring element or like arrangement such as a flapper valve' arrangement in some known pump apparatus.

The control means may be arranged to open the outlet valve as the at least a portion of the compression member moves from the second position to the first position and to close the outlet valve when the at least a portion of the compression member is substantially at the first position thereby to increase the amount of fluid exhausted through the outlet valve.

Thus, the outlet valve can remain open even when the pressure of fluid within the pump chamber is substantially the same as that on the fluid outlet side of the outlet valve, as the at least a portion of the compression member moves towards the first position to compress the fluid and exhaust the fluid from the pump chamber through the outlet valve. Thus the outlet valve can remain open for a longer period compared with valves not actuated by an actuator under the control of a controller.

This is because there is no requirement for a pressure difference to exist across the outlet valve in order to open the outlet valve.

The apparatus may be coupled to first and second respective different volumes and arranged to pump gas from a first volume to the second volume.

The first volume may for example be a chamber or any other suitable volume. For example, a chamber or other volume of a gas storage vessel.

The second volume may be atmosphere, a chamber or any other suitable volume. For example, a chamber or other volume of a different gas storage vessel.

The apparatus may comprise a linear drive assembly operable to drive the at least a portion of the compression member to and fro within the pump chamber.

In conventional pumping apparatus, a rotary-linear drive means and not a linear drive assembly is employed to drive a piston reciprocating within a cylinder. Typically, the rotary-linear drive means employs a crank shaft or similar that is coupled to the piston by means of a connecting rod. Circular motion of the crank shaft is converted to linear motion of the piston by the connecting rod as described above with respect to FIG. 1.

This arrangement suffers the disadvantage that periodic lateral forces are introduced between the piston and the cylinder as the crank shaft rotates and the piston reciprocates.

These lateral forces enhance a rate of wear of the piston and cylinder. The rate of wear is particularly acute in embodiments where lubrication between the piston and cylinder is not or cannot be employed.

The use of a linear drive means, being a drive means in which substantially linear motion is generated directly by the drive means (rather than indirectly through rotation of a crank shaft) has the advantage that a rate of wear of the reciprocating member (such as a piston) and the sidewall of the pump chamber may be reduced.

It is to be understood that bearings supporting the crank shaft of a rotary-linear drive experience considerable loads and severe changes in load direction as the piston reciprocates in the cylinder. This can cause a charge of grease with which the bearings are packed to be urged out from the region in which the bearings are provided.

In conventional lubricant-free apparatus, grease is still required for these bearings and loss of grease in this manner can considerably reduce an expected length of a service life of the apparatus. This is a particular problem for lubricant-free pumps because of the absence of alternative sources of lubricant for the bearings, such as oil migrating from an oil sump of the apparatus.

It is to be understood that in known pumps such as that of FIG. 1 a magnitude of the cosine forces exerted on the sidewall of the cylinder may be reduced if a length of the coupling rod is increased. However, increasing the length of the coupling rod results in an increase in a size (and weight) of the apparatus.

The linear drive assembly may comprise a coupling rod coupled to the compression member, the drive assembly being arranged to drive the coupling rod to and fro in a substantially straight line along a direction coincident with a longitudinal axis of the coupling rod.

Advantageously the drive assembly comprises a piezoelectric drive portion.

As in the case of the electromagnetic drive described above, the piezo-drive may also be arranged to propel the coupling rod in an axial direction to and fro thereby to cause the reciprocating member to execute reciprocal motion within the cylinder.

Use of a linear drive in the form of a piezo-drive has the advantage over an electromagnetic linear drive that a piezo-drive may be configured not to generate an electromagnetic field during operation. This has the advantage that a magnitude of a magnetic field to which a gas being pumped is exposed may be reduced. This is particularly advantageous when it is required to pump certain gases such as hyperpolarised gases since the magnetic field can result in loss of magnetic polarisation of the gas.

Furthermore, in some arrangements a piezo-drive (or plurality of piezo-drives if required) may be arranged to generate a lower amount of heat compared with an electromagnetic drive.

It is to be understood that the amount of heat generated by the linear drive (and in particular a piezo-drive) may arranged to be sufficiently low to allow the drive to be sealed in a vacuum-tight package and operated within a volume of the pump in which the pressure is below atmospheric pressure.

Such operation is not possible with some known drives due to a reduction in the extent to which heat generated by the drive can be dissipated. This is due at least in part to the fact that the gaseous atmosphere in which the drive is operated is below atmospheric resulting in reduced cooling by thermal conduction through the gas. Furthermore, the volume in which the drive is accommodated may be relatively small in order to provide a compact fluid pump apparatus further reducing an extent to which heat can be conducted or otherwise transferred away from the drive.

This can cause the drive to operate at a higher temperature than is desirable and ultimately to fail prematurely.

Use of a piezo-drive has the further advantage that an amount of outgassing of the piezo- drive is less than that of other known linear drives. This is at least in part because piezo-drives may be fabricated substantially entirely from inorganic crystalline material. Thus, organic materials that have a tendency to outgas such as polymeric materials are not required to be used.

Furthermore, piezo-drives may be operated without a requirement for lubrication of the interface between the coupling rod and a remainder of the drive. Thus problems associated with vaporisation of such lubricant may be eliminated.

Furthermore, since the piezo-drive requires only an electrical power supply for its operation, it can be powered by means of an electrical feedthrough from the ambient environment in which the pump apparatus is situated into the vacuum-tight environment within the pump apparatus. That is, no mechanical feedthroughs are required.

Mechanical feedthroughs typically require seals to be provided allowing relative motion between the seal and the feed-through which are prone to wear particularly when lubricant cannot be employed. Other mechanical feedthroughs such as bellows-type arrangements and the like typically experience wear and/or fatigue at a relatively rapid rate and are therefore undesirable for use in pumping applications where repeated reciprocal mechanical motion to drive the piston is required.

It is to be further understood that piezo-drives are capable of providing substantially pure linear translational motion such that substantially no cosine or like lateral forces are exerted by the reciprocating member on the internal wall of the cylinder member as it is caused to reciprocate to and fro within the cylinder member. This has the advantage that an amount of wear of the cylinder member due to reciprocal translation of the reciprocating member may be reduced.

It is to be understood that these lateral forces may be described as radial forces in the case where the internal volume of the cylinder member swept by the reciprocating member is of cylindrical cross-section.

As noted above, since lubricant cannot be employed within the cylinder member between the reciprocating member and internal wall cylinder member it is important to reduce forces (between the reciprocating member and cylinder member) as much as possible.

A further advantage of employing a linear drive is that a stroke and/or a rate of travel of the reciprocating member may be more easily controlled. In contrast, when a crank is used to drive the coupling rod the crank is typically arranged to rotate continuously and at a constant speed. The stroke of the reciprocating member is therefore of a substantially constant length and the speed of the reciprocating member varies in a periodic manner.

In the case of a linear drive, the direction of travel of the coupling rod is changed by halting the coupling rod and reversing the direction of travel. In contrast, in the case of a rotary-linear drive the rotating crank rotates at a substantially constant speed and may have a not inconsiderable inertia in order to provide for smooth operation.

The ability to vary the length of the stroke of the reciprocating has the advantage that the stroke may be changed responsive to one or more parameters such as a pressure of gas to be pumped at the inlet of the pump apparatus and/or a pressure of gas at the outlet.

In some arrangements the stroke may be arranged to increase with increasing pressure at the inlet.

In some arrangements the stroke may be arranged to decrease with increasing pressure at the inlet.

In some arrangements the speed of the reciprocating member over a given stroke may be changed responsive to a pressure of fluid at the inlet or outlet. In some arrangements the speed may be increased as a function of increasing pressure at the inlet. In some arrangements the speed may be decreased as a function of increasing pressure at the inlet.

Other arrangements are also useful Alternatively or in addition the drive assembly may comprise an electromagnetic drive portion.

The linear drive assembly may be provided in fluid communication with the compression member.

This feature has the advantage that a mechanical feed-through between volumes at different respective pressures is not required to be provided. This is because the compression member and linear drive means are in fluid communication with one another. Thus in the case that the apparatus is operated as a vacuum pump, the portion of the compression member in fluid communication with the linear drive assembly will share a common vacuum with the assembly.

By eliminating the requirement to provide a mechanical feedthrough, a risk that fluid pumped by the apparatus leaks out from the apparatus may be reduced. Furthermore, a risk of leakage of fluid into the apparatus thereby mixing with fluid pumped by the apparatus may be reduced.

Still furthermore, a risk of contamination of fluid pumped by the apparatus with lubricant associated with the mechanical feedthrough may be eliminated.

It is to be understood that the mechanical feedthrough may be comprise the coupling rod, the coupling rod passing through a housing of the apparatus such as a housing of the cylinder member.

The linear drive assembly may be provided in a vacuum-tight package and thereby sealed from an environment external to the apparatus.

Advantageously the apparatus is arranged to pump gaseous fluid.

Further advantageously the apparatus is a vacuum pump.

Still further advantageously the apparatus is a dry pump.

In other words, the apparatus is arranged to operate without exposing fluid being pumped to lubricant in the form of a liquid.

Alternatively or in addition the apparatus may be arranged to pump a liquid.

In a further aspect of the invention there is provided a pumping assembly comprising at least first and second fluid pump apparatus according to the preceding aspect.

Advantageously a fluid outlet of the first pump apparatus is in fluid communication with a fluid inlet of the second pump apparatus wherein the first and second pump apparatus are coupled in series.

Optionally respective compression members of the first and second pump apparatus are arranged to reciprocate along a common axis.

Alternatively respective compression members of the first and second pump apparatus are arranged to reciprocate along respective parallel axes.

In a still further alternative respective compression members of the first and second pump apparatus are arranged to reciprocate along non-parallel axes.

Optionally respective compression members of the first and second pump apparatus are arranged to reciprocate along substantially orthogonal axes.

Respective compression members of the assembly may be arranged to reciprocate either in phase or in anti-phase with respect to one another.

In a further aspect of the invention there is provided a method of pumping a fluid by means of pumping apparatus comprising: actuating by actuator means valve means by means of control means and drawing fluid into a cylinder member through the valve means from a fluid inlet of the apparatus by translation of at least a portion of a compression member within the cylinder member in a as first direction; and actuating by actuator means the valve means by the control means and expelling fluid from the cylinder member through the valve means and a fluid outlet of the apparatus by translation of said at least a portion of the compression member in a second direction opposite the first direction.

DESCRIPTION OF THE DRAWINGS

Embodiments of the invention may be understood with reference to the following drawings: FIGURE 1 shows a cross-section of a prior art pump with a piston of the pump at a position approximately midway between BDC and TDC positions; FIGURE 2 is a cross-sectional view of a portion of a pump according to an embodiment of the invention having inlet and outlet valves that may be actuated by means of a respective actuators; FIGURE 3 shows the pump of FIG. 2 including a linear drive for driving a piston of the pump; FIGURE 4 is a cross-sectional view of a pump according to a further embodiment of the invention having inlet and outlet valves and an auxiliary valve in a flow-path of gas between a cylinder member and the inlet and outlet valves; FIGURE 5 is a cross-sectional view of a pump similar to that of the embodiment of FIG. 4 in which the inlet and outlet valves are provided in the form of a shuttle valve assembly; and FIGURE 6 shows a floating coupling between a piston and a coupling rod of a pump according to an embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIG. 2 shows a portion of a pump 600 according to an embodiment of the present invention.

The pump 600 has a cylinder 602 defining a pump chamber 601 within which a piston 610 is reciprocally slidable. A coupling rod 612 is coupled to the piston 610 and arranged to be translated to and fro along a longitudinal axis L of the cylinder 602 by a piezo-actuated linear drive 662 provided within a piston drive module 660 (FIG. 3).

In an alternative embodiment a different type of linear drive may be employed. In some embodiments the linear drive means is or comprises a magnetic drive means. In some embodiments the magnetic drive means has an electromagnet (which may be or include a solenoid coil) through which an alternating current is arranged to be fed. The alternating current generates an alternating magnetic field by means of which the coupling rod 612 is driven back and forth.

A front end 602A of the cylinder 602 has a head block 603 coupled thereto around a periphery of the cylinder 602 to seal the cylinder 602 from an external environment.

The head block 603 has an inlet valve 633 and an outlet valve 631 mounted therein. The valves 633, 631 each have a valve stem 6335, 631S coupled to a valve head 633H, 631 H. Piezo-actuated linear drives 633D, 631 D are provided within a valve drive module 680 and arranged to translate the respective stems 633S, 631S of the valves 633, 631 along a direction parallel to the longitundinal axis L of the cylinder 602. This allows the valves 633, 631 to be moved between open and closed conditions.

The head block 603 has an inlet aperture 691 in fluid communication with the inlet valve 633 and arranged to receive a flow of fluid to be pumped by the pump 600. Fluid flowing through the head block inlet aperture 691 enters an inlet cavity 691C within the head block 603.

When the inlet valve 633 is in the open condition (shown in FIG. 2) fluid may be drawn into the pump chamber 601 through an inlet valve aperture 633 IN.

The head block 603 also has an outlet aperture 695 in fluid communication with the outlet valve 631. When the outlet valve 631 is in the open condition (shown in FIG. 2) fluid is able to flow out of the pump chamber 601 through an outlet valve aperture 6310UT into an outlet cavity 695C within the head block 603. The fluid is then able to exit the head block 603 through the head block outlet aperture 695.

The inlet and outlet cavities 6910, 6950 are in fluid isolation from one another by means of an internal wall 603W of the head 603.

The inlet valve linear drive 633D is operable to urge the head portion 633H of the inlet valve 633 against an inlet valve seat 633A formed in a basal portion 603B of the head block 603 facing the cylinder 602. With the head portion 633H in this position the inlet valve 633 is in a closed condition, whereby the inlet valve aperture 6331N is closed. In the embodiment shown the head portion 633H is in the form of a disc having a diameter that tapers between opposed major surfaces thereof. The inlet valve seat 633A is of a corresponding complementary shape to the head portion 633H allowing a snug fit between the head portion 633H and seat 633A when in the closed condition.

The outlet valve 631 has a corresponding head portion 631 H coupled to the stem 631 S. The head portion 631 H is operable to be urged against an outlet valve seat 631A formed in the basal portion 603B of the head block adjacent the inlet valve seat 633A allowing the valve 633 to assume a closed condition, closing the outlet valve aperture 6310UT.

It is to be understood that because the inlet and outlet valves 633, 631 are each operable to assume open or closed conditions by means of respective piezo-actuated linear drives 633D, 631 D the valves 633, 631 may be opened and closed independently of a difference in pressure of fluid across the respective valves 633, 631.

This feature has the advantage that the valves may be opened and closed at different times and for longer or shorter periods of time than might otherwise be possible in order to improve performance of the pump 600.

Thus it is to be understood that when the piston 610 is at or near its position of closest approach to the head block 603 (a position that will be referred to as top dead centre' or TDC, although this expression is to be understood as not limiting an orientation of the pump in use), the outlet valve 631 may be closed. The precise position of the piston 610 at which the outlet valve 631 is closed may be controlled in order to optimise the amount of gas expelled before the inlet valve 633 is opened.

It is to be understood that the inlet valve 633 may be opened at any suitable moment in time independently of the position of the outlet valve 631 and piston 610. Thus it is to be understood that the inlet valve 633 may be opened relatively soon after (or at substantially the same time as) the outlet valve 631 is closed. Other arrangements are also useful.

Opening of the inlet valve 633 when or soon after TDC has been reached has the advantage that the piston 610 is not required to pull against a closed pump chamber 601 before gas to be pumped is allowed to flow into the pump chamber 601. It is to be understood that an amount of force required to pull the piston 610 from the TDC position is higher when the inlet valve 633 is closed compared to when the inlet valve 633 is open. Since the force required to be developed by the piezo-actuated linear drive 662 may be reduced in this way a linear drive 662 having a reduced drive force capability may be employed.

Furthermore, because the inlet and outlet valves 633, 631 are actuated by respective piezo-actuated linear drives 633D, 631 D the force with which each valve head 633H, 631 H is urged against the corresponding valve seat 633A, 631A may also be controlled independently of the pressure difference across the respective valves 633, 631.

It is to be understood that in known pumps the inlet and outlet valves are urged to the closed condition by means of a spring element and/or by a difference in pressure across the valve.

Embodiments of the present invention are advantageous over arrangements in which spring elements are employed because spring elements can deteriorate in their effectiveness over time and suffer wear due to lack of lubrication. Furthermore, in order to open the valve a pressure difference across the valve must be sufficient to overcome the closure force of the spring. In contrast, embodiments of the present invention allow the inlet and outlet valves 633, 631 to be opened independently of the pressure difference and without a requirement for spring elements.

Spring elements also suffer the disadvantage that heat is generated due to flexure of the spring elements and sliding contact between the spring elements and other surfaces with which they are in contact.

It is to be understood that in the embodiment of FIG. 2, because the inlet valve 633 is actuated by an actuator 633D it is capable of opening by movement of the valve head 633H against the direction of flow of fluid into the cylinder 602 when it is required to allow fluid to pass into the cylinder 602. This is in contrast to conventional sprung valves in which displacement of the valve head 633H occurs in the direction of fluid flow due to a difference in pressure between fluid on opposite sides of the head 633H. Thus the inlet valve head 633H does not intrude into the cylinder 602 thereby increasing a dead space between the piston 610 and head 603 when the piston 610 is at TDC.

Embodiments of the present invention involve only sliding contact between the valve stems 633S, 631 S and respective actuators 633D, 631 D or between the coupling rod 612 and actuator 662. Therefore an amount of heat required to be dissipated by the pump 600 is significantly reduced, particularly the amount within the head block 603.

A further advantage of employing piezo-actuators to open and close the valves 633, 631 is that the valves 633, 631 may be arranged to have high opening and closing forces even when no power is applied to the respective actuator 633D, 631 D. Thus, the valve head 633H, 631H may be moved to abut the valve seat 633A, 631A and to be urged against the valve seat 633A, 631A with a relatively high force. If power to the actuator 684, 682 is then terminated the valve head 633H, 631H will remain urged against the seat 633A, 631A. This allows a high integrity seal to be formed between the head 633H, 631 H and seat 633A, 631 A to prevent leakage therepast.

Conversely, the valve head 633H, 631H may be translated away from the seat 633A, 631A with a relatively high force if required.

Furthermore, it is to be understood that inlet and outlet valves actuated by means of piezo-actuators may be fabricated from non-magnetic materials and materials that do not outgas (or which outgas by a relatively insignificant amount). The use of non-magnetic materials can be particularly useful in certain applications, for example applications in which polarised gases are pumped such as spin-polarised gases. Likewise a low-outgassing property enables applications in high vacuum applications and applications where contamination of a gas being pumped is highly undesirable.

Embodiments of the invention employing piezo-actuated linear drives have the advantage that relatively high opening and closing rates may be obtained allowing high opening and closing repetition rates.

In some arrangements a controller arranged to control opening and closing of the inlet and outlet valves 633, 631 is provided with a signal responsive to a position of the piston 610.

The signal may be derived from a drive signal for the piezo-drive 662 driving the piston 610 or from a measurement of a position of the piston 610, for example by means of a sensor such as an optical sensor. One or more pressure sensors may also be provided generating signals responsive to which the controller may control operation of the valves 633, 631. For example, one or more sensors may be arranged to sense pressure within the pump chamber 601, and/or in or near one or both of the inlet and outlet chambers 691 C, 6950.

In some arrangements an electromagnetic, acoustic or other signal is employed to determine a position of the piston 610, for example by means of a Doppler shift between a transmitted signal and a received signal. The measurement may be made at a location external to the environment of the pump chamber 601 or within the same atmosphere as the pump chamber 601.

Other arrangements are also useful.

It is to be understood that in the embodiment of FIG. 2 and FIG. 3 the head block 603 and piezo-actuated linear drives 633D, 631 D for the inlet and outlet valves 633, 631 respectively may be provided in a vacuum-tight package which will be referred to as a valve drive module 680 (FIG. 3). An electrical feed-through element 688 is provided to allow electrical power to be provided to the actuators 633D, 631 D within the sealed valve drive module 680.

By vacuum-tight package is meant that the package is capable of preventing air from leaking from an outside of the package to an interior of the package where the actuators are located.

In some arrangements the vacuum-tight package is a helium gas Ieakproof package, i.e. helium gas present on an external surface of the package is not able to leak into the package.

Similarly, the piezo-actuated linear drive 662 for driving the piston 610 is also provided within a vacuum-tight package of a piston drive module 660. An electric feedthrough 668 is provided allowing electrical power to be provided to the drive 662.

In some arrangements the piezo-actuated linear drives 6330, 631 D, 662 are provided in a common vacuum-tight package.

In some arrangements a common controller controls operation of each of the piezo-actuated linear drives 6330, 6310, 662. Thus opening and closing of the valves 633, 631 may be readily coordinated with the reciprocal translation of the piston 610.

As noted above the position of the piston 610 at a given moment in time may be determined by means of an optical or other sensor. The position of the piston 610 may be determined by reference to the piston 610 itself or to the coupling rod 612 which forms part of the piezo-actuated linear drive 668 in the arrangement shown.

Other arrangements are also useful.

FIG. 4 shows a pump 700 according to an alternative embodiment of the invention. Again, like features of the embodiment of FIG. 4 to those of the embodiment of FIG. 2 are shown with like reference signs prefixed numeral 7 instead of numeral 6.

The pump 700 differs from that of the embodiment of FIG. 2 and FIG. 3 in that a single auxiliary valve 741 is provided in the basal portion 703B of the head block 603 to allow fluid to flow into or out from the cylinder 702.

The auxiliary valve 741 has a head portion 741 H arranged to be urged against a single valve seat 741A provided in the basal portion 703B of the head block 703 by an auxiliary valve stem 741S. A piezo-drive 741D is provided to translate the stem 741S to an fro along an axis of the valve 741 to open and close the valve.

Respective inlet and outlet valves 733, 731 are provided in the head block 703 in a flow-path of fluid between the auxiliary valve 741 and the fluid inlet and fluid outlet 791, 795 respectively. The inlet and outlet valves 733, 731 are arranged to be actuated by means of respective linear drives 733D, 731 0. In the embodiment of FIG. 13 the linear drives 741 0, 7330, 731 D are piezo-actuated linear drives.

An auxiliary valve chamber 741C is provided in fluid communication with the inlet and outlet valve heads 733 H, 731 H and auxiliary valve head 741 H. Fluid flowing into or out from the cylinder 702 is arranged to flow through the auxiliary valve chamber 741 C. In use the pump 700 may be operated as follows.

With the piston 710 at its position of closest approach to the head block 703 of the pump 700 the outlet valve 731, auxiliary valve 741 and inlet valve 733 are all closed. The auxiliary valve 741 and inlet valve 733 are then opened and the piston 710 translated away from the head block 703 to draw fluid into the cylinder 702 through the inlet valve 733.

lt is to be understood that the order in which the inlet valve 733 and auxiliary valve 741 are opened and the precise moment at which they are opened may be determined so as to optimise a performance of the pump 700. Thus in some arrangements the inlet valve 733 may be opened before the auxiliary valve 741 is opened. In some alternative arrangements the inlet valve 733 may be opened after the auxiliary valve 741 has been opened.

When the piston 710 reaches its furthest distance of travel from the head block 703 the auxiliary valve 741 and inlet valve 733 are both closed. Again, the order in which the auxiliary valve 741 and inlet valve 733 are closed and the precise moment at which they are closed may be determined so as to optimise performance of the pump 700.

The piston 710 then begins to travel back towards the head block 703 compressing fluid present in the cylinder 702. The auxiliary valve 741 and outlet valve 731 are then opened to allow compressed fluid to be exhausted from the cylinder 702. The order in which the auxiliary valve 741 and outlet valve 731 are opened and the precise moment at which the valves 741, 731 are opened may be determined so as to optimise performance of the pump 700.

As the piston 710 approaches the head block 703 or when the piston 710 reaches its position of closest approach to the head block 703 the inlet valve 733 and auxiliary valve 741 are closed. In some arrangements the valves 733, 741 may be closed after the piston 710 reaches its position of closest approach and has remained substantially stationary for a prescribed period to allow time for compressed gas to flow out from the cylinder 702. Other arrangements are also useful.

It is to be understood that the order in which the auxiliary valve 741 and outlet valve 731 are closed and the precise moment at which the valves 741, 731 are closed may be determined so as to optimise performance of the pump 700.

FIG. 5 shows a pump 800 according to a further embodiment of the invention. The embodiment of FIG. 5 is similar to that of FIG. 4 except that the inlet and outlet valves 733, 731 of the embodiment of FIG. 4 are replaced by a shuttle valve assembly 835.

Like features of the embodiment of FIG. 5 to the embodiment of FIG. 4 are shown with like reference signs prefixed numeral 8 instead of numeral 7.

As may be seen in FIG. 5 the shuttle valve assembly 835 has an inlet conduit 835 IN coupled to the fluid inlet 891 of the pump 800 and an outlet conduit 8350UT coupled to a fluid outlet 895 of the pump 800.

The assembly 835 has a single inlet/outlet conduit 8350 in fluid communication with the auxiliary valve 841.

A shuttle element 835H is provided within the assembly 835. A shuttle drive 831D in the form a linear piezo-actuator is coupled to the shuttle element 835H by means of a stem 835S. The drive 831 D is arranged to drive shuttle element 835H back and forth within the assembly 835 between the fluid inlet and outlet conduits 8351N, 8350UT respectively.

In a first position A of the shuttle element 835H (shown in solid outline in FIG. 5) the shuttle element 835H closes the inlet conduit 8351N thereby preventing flow of fluid to the auxiliary valve 841 from the fluid inlet 891. In this position of the shuttle element 835H the outlet conduit 8350UT is open allowing fluid to flow from the auxiliary valve 841 to the fluid outlet 895.

In a second position B of the shuttle element 835H (shown in dotted outline in FIG. 5) the shuttle element 835H closes the outlet conduit 8350UT thereby preventing flow of fluid out of the cylinder 802. In this position of the shuttle element 835H the inlet conduit 8351N is open allowing fluid to flow to the auxiliary valve 841 from the fluid inlet 891.

It is to be understood that in use the piston 810 is caused to reciprocate to and fro within the cylinder 802. As it does so the auxiliary valve 841 is opened and closed in concert with movement of the shuttle element 835 to selectively allow fluid to flow into the cylinder 802 from the fluid inlet 891 and to flow out from the cylinder 802 to the fluid outlet 895.

It is to be understood that the precise moments at which the auxiliary valve 841 is opened and closed, the shuttle element 835H of the shuttle assembly 835 translated to and fro and the piston 810 translated to and fro within the cylinder 802 may be selected to optimise fluid pump operation in a given set of circumstances. A pattern of actuation of the various components may be arranged to adapt to the pressure of fluid at the inlet 891, a pressure difference between the inlet and outlets 891, 895 or any other suitable parameter.

Embodiments of the invention have the advantage that fluid pump apparatus may be provided that is capable of operation in a more efficient manner. This is at least in part because the inlet and outlet valve arrangement is controlled by means of actuators.

Furthermore, the use of ceramic-based actuators such as piezoelectric materials has the advantage that reduced contamination of gases being pumped may be achieved. In some arrangements the use of ceramic-based actuators allows pumping of gases that would otherwise react with materials such as metallic materials from which valves are typically constructed.

Some embodiments of the invention have the further advantage that a head portion and/or a piston drive portion may be provided within the same atmosphere as the cylinder 802. This eliminates the need for mechanical feedthroughs enabling an increase in reliability and decrease in risk of contamination of fluid being pumped by gas leakage into the pump or out-gassing of lubricant or other materials associated with the feedthroughs.

Furthermore, in some embodiments a floating piston' arrangement is employed. In such an arrangement, the piston 110, 210 is permitted to have some freedom of movement in a lateral direction relative to the coupling rod 112, 212. In other words, the piston 110, 210 is permitted to move in a direction towards the sidewall 102, 202 of the pump 100, 200. This feature has the advantage that a certain amount of misalignment of a direction of drive of the piston 110, 210 by a linear drive means relative to the longitudinal axis lOlA, 201A of the pump chamber 101, 201 may be compensated for by relative movement between the piston 110,210 and the coupling rod 112,212.

In some embodiments a floating piston' arrangement is employed in which relative lateral movement of a piston 910 is allowed with respect to the coupling rod 912.

FIG. 6 shows an example of such an embodiment. In the arrangement shown a coupling rod 912 is coupled to a piston 910 by means of a resilient float element 911 in the form of a substantially S-shaped element. The float element 911 is arranged to be axially stiff in the sense that the float element 911 has a relatively large resistance to compression along a direction between the piston 910 and the coupling rod 912 (i.e. parallel to cylinder axis L).

However, the float element 911 is arranged to allow lateral movement of the piston relative to the coupling rod 912 (i.e. in a direction normal to cylinder axis L) thereby to prevent a build-up of an excessive lateral force between the piston 910 and cylinder sidewall 902.

This has the advantage that wear of the piston 910 and sidewall 902 may be reduced.

The embodiment of FIG. 6 is also arranged such that rubbing or sliding movement between the piston 910 and float element 911 and rubbing or sliding movement between the float element 911 and coupling rod 912 are substantially prevented. This has the advantage of reducing wear for the reasons discussed above.

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of the words, for example "comprising" and "comprises", means "including but not limited to", and is not intended to (and does not) exclude other moieties, additives, components, integers or steps.

Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.

Claims

CLAIMS: 1. Fluid pump apparatus comprising: a fluid inlet and a fluid outlet; at least one cylinder member having an internal wall defining an internal volume thereof; a compression member provided within the internal volume of the cylinder member; and valve means arranged to be actuated by actuator means under the control of control means, the valve means being operable selectively to allow fluid either to be drawn from the fluid inlet and into the cylinder member by translating at least a portion of the compression member in a first direction or to be exhausted from the cylinder member through the fluid outlet by translating said at least a portion of the compression member in a second direction opposite the first.
2. Apparatus as claimed in claim 1 comprising an inlet valve through which fluid may be drawn into the cylinder member from the fluid inlet and an outlet valve through which fluid may be expelled from the cylinder member to the fluid outlet, each valve having a closure member operable to open or close the valve thereby to allow or prevent flow of fluid thereth rough.
3. Apparatus as claimed in claim 2 wherein at least one of the inlet and outlet valves are actuated by the actuator means.
4. Apparatus as claimed in claim 3 wherein both the inlet valve and the outlet valve are actuated by the actuator means.
5. Apparatus as claimed in claim 4 wherein the inlet and outlet valves are provided with respective different closure elements.
6. Apparatus as claimed in claim 4 wherein the inlet and outlet valves share a common closure element, the closure element being operable by the actuator means to move between a first position in which the inlet valve is open and the outlet valve is closed and a second position in which the inlet valve is closed and the outlet valve is open.
7. Apparatus as claimed in any one of claims 2 to 6 wherein the valve means further comprises an auxiliary valve, the auxiliary valve being provided in a flow-path of fluid between the inlet and outlet valves and the cylinder member such that fluid flowing into or out from the cylinder member flows through the auxiliary valve, the auxiliary valve being operable by the actuator means to prevent a flow of fluid into or out from the cylinder member.
8. Apparatus as claimed in any preceding claim wherein the actuator means comprises at least one drive unit.
9. Apparatus as claimed in claim 8 as depending through claim 5 wherein the actuator means comprises a first drive unit operable to open and close the inlet valve and a second drive unit operable to open and close the outlet valve.
10. Apparatus as claimed in claim 8 or 9 depending through claim 7 wherein the actuator means comprises a drive unit operable to open and close the auxiliary valve.
11. Apparatus as claimed in any one of claims 8 to 10 wherein the drive unit comprises a piezo-electric drive.
12. Apparatus as claimed in any one of claims 8 to 11 wherein the drive unit comprises an electromagnetic drive.
13. Apparatus as claimed in any one of claims 8 to 12 wherein the drive unit comprises an electric motor.
14. Apparatus as claimed in any preceding claim wherein the valve means is provided in a head portion of the apparatus facing the compression member.
15. Apparatus as claimed in any preceding claim comprising sensor means for sensing a position of the compression member, the control means being arranged to control the actuator means responsive to the position of the compression member.
16. Apparatus as claimed in claim 15 wherein the sensor means comprises at least one selected from amongst an optical sensor, a magnetic sensor, an acoustic transducer and an electromagnetic radiation sensor.
17. Apparatus as claimed in claim 15 or claim 16 arranged to sense a position of the sensor by detection of a signal generated by a transmitter and received by a receiver following reflection from the compression member, the signal being one selected from amongst an optical signal, an acoustic signal and an electromagnetic signal.
18. Apparatus as claimed in claim 17 arranged to sense the position of the sensor by reference to an amount of a Doppler shift between the transmitted and received signals.
19. Apparatus as claimed in any preceding claim comprising sensor means for sensing a pressure of fluid in the cylinder member, the control means being arranged to control the actuator means responsive to the pressure of fluid in the cylinder member.
20. Apparatus as claimed in any preceding claim wherein the at least a portion of the compression member is arranged to reciprocate between a first position proximate the valve means and a second position distal the valve means.
21. Apparatus as claimed in claim 20 wherein the control means is operable to control the valve means to allow a flow of fluid into the cylinder member from the fluid inlet when the at least a portion of the compression member moves from the first position towards the second position thereby to reduce a magnitude of a force required to so move the compression member.
22. Apparatus as claimed in claim 2 or any one of claims 3 to 21 depending through claim 2 wherein the control means is arranged to open the outlet valve as the at least a portion of the compression member moves from the second position to the first position and to close the outlet valve when the at least a portion of the compression member is substantially at the first position thereby to increase the amount of fluid exhausted through the outlet valve.
23. Apparatus as claimed in any preceding claim coupled to first and second respective different volumes and arranged to pump gas from a first volume to the second volume.
24. Apparatus as claimed in any preceding claim comprising a linear drive assembly operable to drive the at least a portion of the compression member to and fro within the pump chamber.
25. Apparatus as claimed in claim 24 wherein the linear drive assembly comprises a coupling rod coupled to the compression member, the drive assembly being arranged to drive the coupling rod to and fro in a substantially straight line along a direction coincident with a longitudinal axis of the coupling rod.
26. Apparatus as claimed in claim 24 or 25 wherein the drive assembly comprises a piezoelectric drive portion.
27. Apparatus as claimed in any one of claims 24 to 26 wherein the drive assembly comprises an electromagnetic drive portion.
28. Apparatus as claimed in any one of claims 24 to 27 wherein the linear drive assembly is in fluid communication with the compression member.
29. Apparatus as claimed in claim 28 wherein the linear drive assembly is provided in a vacuum-tight package and thereby sealed from an environment external to the apparatus.
30. Apparatus as claimed in any preceding claim wherein the apparatus is arranged to pump gaseous fluid.
31. Apparatus as claimed in any preceding claim wherein the apparatus is a vacuum pump.
32. Apparatus as claimed in any preceding claim wherein the apparatus is a dry pump.
33. Apparatus as claimed in any preceding claim arranged to pump a liquid.
34. A pumping assembly comprising at least first and second fluid pump apparatus as claimed in any preceding claim.
35. An assembly as claimed in claim 34 wherein a fluid outlet of the first pump apparatus is in fluid communication with a fluid inlet of the second pump apparatus wherein the first and second pump apparatus are coupled in series.
36. An assembly as claimed in claim 34 or 35 wherein respective compression members of the first and second pump apparatus are arranged to reciprocate along a common axis.
37. An assembly as claimed in claim 34 or 35 wherein respective compression members of the first and second pump apparatus are arranged to reciprocate along respective parallel axes.
38. An assembly as claimed in claim 34 or 35 wherein respective compression members of the first and second pump apparatus are arranged to reciprocate along non-parallel axes.
39. An assembly as claimed in claim 38 wherein respective compression members of the first and second pump apparatus are arranged to reciprocate along substantially orthogonal axes.
40. An assembly as claimed in any one of claims 34 to 39 wherein the respective compression members are arranged to reciprocate either in phase or in anti-phase with respect to one another.
41. A method of pumping a fluid by means of pumping apparatus comprising: actuating by actuator means valve means by means of control means and drawing fluid into a cylinder member through the valve means from a fluid inlet of the apparatus by translation of at least a portion of a compression member within the cylinder member in a first direction; and actuating by actuator means the valve means by the control means and expelling fluid from the cylinder member through the valve means and a fluid outlet of the apparatus by translation of said at least a portion of the compression member in a second direction opposite the first direction.
42 Fluid pump apparatus substantially as hereinbefore described with reference to the accompanying drawings.
43. An assembly substantially as hereinbefore described with reference to the accompanying drawings.
44. A method substantially as hereinbef ore described with reference to the accompanying drawings.Amendments to claims have been filed as follows CLAIMS: 1. Dry gaseous fluid pump apparatus comprising: a fluid inlet and a fluid outlet; at least one cylinder member having an internal wall defining an internal volume thereof; a compression member provided within the internal volume of the cylinder member; and valve means arranged to be actuated by actuator means under the control of control means, the valve means being operable selectively to allow fluid either to be drawn from the fluid inlet and into the cylinder member when at least a portion of the compression member is translated in a first direction or to be exhausted from the cylinder member through the fluid outlet when said at least a portion of the compression member is translated in a second direction opposite the first, the apparatus comprising a linear drive assembly operable to drive the at least a portion of the compression member to and fro within the cylinder member, and r sensor means for sensing a position of the compression member, the control means being arranged to control the actuator means responsive to the position of the compression member.C2. Apparatus as claimed in claim 1 comprising an inlet valve through which fluid may be drawn into the cylinder member from the fluid inlet and an outlet valve through which fluid may be expelled from the cylinder member to the fluid outlet, each valve having a closure member operable to open or close the valve thereby to allow or prevent flow of fluid thereth rough.3. Apparatus as claimed in claim 2 wherein at least one of the inlet and outlet valves are actuated by the actuator means.4. Apparatus as claimed in claim 3 wherein both the inlet valve and the outlet valve are actuated by the actuator means.5. Apparatus as claimed in claim 4 wherein the inlet and outlet valves are provided with respective different closure elements.6. Apparatus as claimed in claim 4 wherein the inlet and outlet valves share a common closure element, the closure element being operable by the actuator means to move between a first position in which the inlet valve is open and the outlet valve is closed and a second position in which the inlet valve is closed and the outlet valve is open.7. Apparatus as claimed in any one of claims 2 to 6 wherein the valve means further comprises an auxiliary valve, the auxiliary valve being provided in a flow-path of fluid between the inlet and outlet valves and the cylinder member such that fluid flowing into or out from the cylinder member flows through the auxiliary valve, the auxiliary valve being operable by the actuator means to prevent a flow of fluid into or out from the cylinder member.8. Apparatus as claimed in any preceding claim wherein the actuator means comprises at least one drive unit.9. Apparatus as claimed in claim 8 as depending through claim 5 wherein the actuator means comprises a first drive unit operable to open and close the inlet valve and a second drive unit operable to open and close the outlet valve.LU10. Apparatus as claimed in claim 8 or 9 depending through claim 7 wherein the actuator means comprises a drive unit operable to open and close the auxiliary valve. r11. Apparatus as claimed in any one of claims 8 to 10 wherein the drive unit comprises a piezo-electric drive.12. Apparatus as claimed in any one of claims 8 to 11 wherein the drive unit comprises an electromagnetic drive.13. Apparatus as claimed in any one of claims 8 to 12 wherein the drive unit comprises an electric motor.14. Apparatus as claimed in any preceding claim wherein the valve means is provided in a head portion of the apparatus facing the compression member.15. Apparatus as claimed in any preceding claim wherein the sensor means comprises at least one selected from amongst an optical sensor, a magnetic sensor, an acoustic transducer and an electromagnetic radiation sensor.16. Apparatus as claimed in any preceding claim arranged to sense a position of the sensor by detection of a signal generated by a transmitter and received by a receiver following reflection from the compression member, the signal being one selected from amongst an optical signal, an acoustic signal and an electromagnetic signal.17. Apparatus as claimed in claim 16 arranged to sense the position of the sensor by reference to an amount of a Doppler shift between the transmitted and received signals.18. Apparatus as claimed in any preceding claim comprising sensor means for sensing a pressure of fluid in the cylinder member, the control means being arranged to control the actuator means responsive to the pressure of fluid in the cylinder member.19. Apparatus as claimed in any preceding claim wherein the at least a portion of the compression member is arranged to reciprocate between a first position proximate the valve means and a second position distal the valve means. c\J20. Apparatus as claimed in claim 19 wherein the control means is operable to control LIt) the valve means to allow a flow of fluid into the cylinder member from the fluid inlet when the at least a portion of the compression member moves from the first position towards the second position thereby to reduce a magnitude of a force required to so move the compression member.21. Apparatus as claimed in claim 2 or any one of claims 3 to 20 depending through claim 2 wherein the control means is arranged to open the outlet valve as the at least a portion of the compression member moves from the second position to the first position and to close the outlet valve when the at least a portion of the compression member is substantially at the first position thereby to increase the amount of fluid exhausted through the outlet valve.22. Apparatus as claimed in any preceding claim coupled to first and second respective different volumes and arranged to pump gas from a first volume to the second volume.23. Apparatus as claimed in any preceding claim wherein the linear drive assembly comprises a coupling rod coupled to the compression member, the drive assembly being arranged to drive the coupling rod to and fro in a substantially straight line along a direction coincident with a longitudinal axis of the coupling rod.24. Apparatus as claimed in any preceding claim wherein the drive assembly comprises a piezoelectric drive portion.25. Apparatus as claimed in any preceding claim wherein the drive assembly comprises an electromagnetic drive portion.26. Apparatus as claimed in any preceding claim wherein the linear drive assembly is in fluid communication with the compression member.27. Apparatus as claimed in any preceding claim wherein the linear drive assembly is provided in a vacuum-tight package and thereby sealed from an environment external to the apparatus.28. Apparatus as claimed in any preceding claim wherein the apparatus is a vacuum pump. c\J29. A pumping assembly comprising at least first and second fluid pump apparatus as LI) claimed in any preceding claim.30. An assembly as claimed in claim 29 wherein a fluid outlet of the first pump apparatus is in fluid communication with a fluid inlet of the second pump apparatus wherein the first and second pump apparatus are coupled in series.31. An assembly as claimed in claim 29 or 30 wherein respective compression members of the first and second pump apparatus are arranged to reciprocate along a common axis.32. An assembly as claimed in claim 29 or 30 wherein respective compression members of the first and second pump apparatus are arranged to reciprocate along respective parallel axes.33. An assembly as claimed in claim 29 or 30 wherein respective compression members of the first and second pump apparatus are arranged to reciprocate along non-parallel axes.34. An assembly as claimed in claim 33 wherein respective compression members of the first and second pump apparatus are arranged to reciprocate along substantially orthogonal axes.35. An assembly as claimed in any one of claims 29 to 34 wherein the respective compression members are arranged to reciprocate either in phase or in anti-phase with respect to one another.36. A method of dry pumping a gaseous fluid by means of dry pumping apparatus comprising: actuating by actuator means valve means by means of control means and drawing fluid into a cylinder member through the valve means from a fluid inlet of the apparatus by translation of at least a portion of a compression member within the cylinder member in a first direction; and actuating by actuator means the valve means by the control means and expelling fluid from the cylinder member through the valve means and a fluid outlet of the apparatus by translation of said at least a portion of the compression member in a second direction opposite the first direction, wherein the steps of translating the compression member in the first and second directions comprises translating the compression member by means of a linear drive means, and LI) wherein the method further comprises sensing by means of sensor means a position of the compression member and controlling the actuator means responsive to the position of the compression member. r37. Fluid pump apparatus substantially as hereinbefore described with reference to the accompanying drawings.38. An assembly substantially as hereinbefore described with reference to the accompanying drawings.39. A method substantially as hereinbefore described with reference to the accompanying drawings.