EP3786453A1

EP3786453A1 - Apparatus and method

Info

Publication number: EP3786453A1
Application number: EP19194992.4A
Authority: EP
Inventors: Allan McDiarmid
Original assignee: Individual
Current assignee: Individual
Priority date: 2019-09-02
Filing date: 2019-09-02
Publication date: 2021-03-03

Abstract

The application relates to an apparatus (10) and a method for generation of a partial vacuum within a sealed volume. The apparatus comprises a twin screw compressor (30), having an inlet (8) communicable with a sealed volume and an outlet. The twin screw compressor (30) is operable to accept fluid through the inlet (8), compress the fluid and vent the compressed fluid through the outlet. A valve member (1) is associated with the twin screw compressor (30) and movable to vary the outlet volume, and is actuable automatically in response to an inlet/outlet pressure differential. Advantageously, the apparatus (10) provides a means for automatically controlling the effective inbuilt volume ratio of a screw compressor without requiring a separate valve control system.

Description

The present invention relates to an apparatus and a method for vacuum generation, particularly, but not exclusively, a twin screw compressor comprising a means for automatically varying outlet volume in response to a predetermined pressure differential across the screw compressor to thereby minimise compression power for a range of differential pressures.
Vacuum pumps for removing gas molecules from a sealed volume to achieve a substantial or partial vacuum are well known. Rotary screw compressors can be used to draw a working fluid from the sealed volume via an inlet and compress the working fluid using a rotary positive displacement mechanism to discharge the compressed working fluid via an outlet to thereby create a partial vacuum within the sealed volume. When vacuum compressors operate at high vacuum inlet, a significant proportion of the input power is used in pumping the exhaust volume back and forth from the screw rotors exhaust volume into the exhaust line with each rotor lobe discharge. In order to minimise the power requirements of the pump, it is beneficial to minimise the exhaust volume. However, at high inlet pressures (such as atmospheric pressure) with a small exhaust volume, the internal compression generated within the compressor can be excessively high resulting in increased power and bearing loads.
In large vacuum formation applications, such as refrigeration, the inbuilt volume ratio of the compressor may be varied to adjust the power requirements according to the input/output pressure differential. This is achieved using an externally actuated and controlled slide valve to vary both the inlet volume and the position of the exhaust port. The slide valve bore extends over the length of the rotary screw compressor rotors and the slide valve is typically controlled by an oil pump or separate control system.
According to a first aspect of the invention, there is provided an apparatus for generation of a partial vacuum within a sealed volume, the apparatus comprising:

a twin screw compressor, having an inlet communicable with a sealed volume and an outlet, wherein the twin screw compressor is operable to accept fluid through the inlet, compress the fluid and vent the compressed fluid through the outlet; and
a valve member associated with the twin screw compressor and movable to vary the outlet volume, wherein the valve member is automatically actuable in response to an inlet/outlet pressure differential.

Thus, the apparatus of the invention is advantageous since it provides a means for automatically controlling the effective inbuilt volume ratio of a screw compressor without requiring a separate valve control system.
Optionally, the valve member is associated with and located in the region of the outlet to selectively vary the outlet volume and hence change the inlet/outlet volume ratio.
Positioning the movable valve member at the compressor outlet advantageously enables the screw compressor to work effectively to create and also to maintain a vacuum while minimising the compression power over a wide range of differential inlet/outlet pressure ratios by automatically managing inlet/outlet volume ratios. In addition, this positioning of the valve member in the region of the compressor outlet substantially prevents leakage across the valve member as there is no direct leak path across the length of the screw compressor.
Optionally the valve member is moveable between a first configuration in which the outlet volume is reduced and a second configuration in which the outlet volume is increased.
Optionally, the valve member is movable to reduce the outlet volume at high differential inlet/outlet pressures. Thus, at high differential inlet/outlet pressures, the valve member may be movable into the first configuration. Optionally, the valve member may be moveable to a closed configuration at high differential inlet/outlet pressures. The first configuration may be a closed configuration.
A high differential pressure may occur as a result of low pressure or partial vacuum within the sealed chamber. Advantageously, the apparatus provides a means for reducing the power consumption and bearing loads on the compressor with low inlet pressures.
Optionally, the valve is movable to increase the outlet volume at a low differential inlet/outlet pressures. Thus, at low differential inlet/outlet pressures, the valve member may be movable into the second configuration. Optionally, the valve member may be movable to an open configuration at low differential inlet/outlet pressures. The second configuration may be an open configuration.
A low differential pressure may occur as a result of relatively high pressure in the sealed chamber, such as when the sealed chamber is at ambient pressure prior to actuation of the apparatus and operation of the screw compressor. Thus, the apparatus is arranged to provide a means for minimising the power consumption with high inlet pressures.
Optionally, the valve member is arranged to transition between the first and second configurations at a predetermined inlet/outlet pressure differential. Optionally, the valve member is arranged to move between the open and closed configurations at a predetermined inlet/outlet pressure differential.
Optionally, the valve member is biased into a particular configuration. The valve member may be biased into either the first or the second configuration. Optionally, the valve member is biased into the first configuration in which the outlet volume is increased relative to the inlet volume. Optionally, the valve member is biased into an open configuration to increase the outlet volume at low inlet/outlet differential pressures.
Optionally, the apparatus comprises a biasing means for biasing the valve member into a predetermined configuration. Optionally the force of the biasing means is preselected to enable the valve member to transition between the first and second configurations at a predetermined inlet/outlet pressure differential.
Optionally, the biasing means is provided to bias the valve into the first configuration. Optionally the biasing force is preselected according to factors including but not limited to; the application, compressor type, and/or output characteristics. Optionally, the valve is biased into the first configuration with a predetermined force. Optionally, the first configuration is an open or bypass position.
The biasing means may act directly or indirectly on the valve member. Optionally, the biasing means comprise a resilient means arranged to act on the valve member to bias the valve member into the first configuration. The resilient means may comprise a spring.
Alternatively, the biasing means may include gravity and the apparatus may be arranged in use such that the valve member is in an orientation where gravity acts to retain the valve member in a particular configuration. The apparatus may be arranged in a substantially vertical orientation in use, and the biasing means may include gravity.
For some applications, it is advantageous to bias the valve member in the open configuration, since prior to actuation of the apparatus and the screw compressor, both the sealed volume and the outlet pressure is likely to be ambient pressure and closely matched. Thus, the apparatus is initially configured to minimise power requirements, where there is a low or minimal inlet/outlet pressure differential.
Optionally, the valve member is selectively slideable to vary the outlet volume. Optionally, the valve member is a slide valve.
Optionally, the apparatus comprises a valve control mechanism for controlling movement of the valve member based on the differential inlet/outlet pressure. Optionally, the valve control mechanism is coupled to the valve member such that movement of the valve control mechanism is translated to the valve member. Optionally the valve control mechanism is automatically responsive to the differential inlet/outlet pressure.
Optionally the valve control mechanism comprises an actuation member exposed to inlet and outlet pressure, said actuation member being movable by an inlet/outlet differential pressure of a predetermined value.
Optionally, the actuation member comprises a piston movable within a chamber, wherein a first face of the piston is exposed to inlet pressure and a second opposing face of the piston is exposed to outlet pressure. Optionally, the piston is coupled to the valve member via a connecting member. The connecting member may be a connecting rod.
The valve control mechanism is advantageous, since it provides a means for automatically varying the inlet/outlet volume and thereby the internal compression of the compressor. The valve control mechanism is responsive to differential pressures across the compressor without the need for a separate control system.
Optionally, the apparatus further comprises a damping system. The damping system may be associated with the valve member and/or valve control mechanism. Optionally, the damping system is arranged to substantially restrict application of large forces to the valve.
Optionally, the damping system comprises a flow restrictor. Optionally, the flow restrictor substantially restricts flow of fluid to and/or from, at least one of the valve member and the valve control mechanism. Optionally, the side of the valve control mechanism and/or valve member exposed to inlet pressure may be provided with a flow restrictor.
The damping system is advantageous since it substantially restricts shock loads from being applied to the valve control mechanism and/or the valve member.
The anticipated applications of the invention include formation and maintenance of a vacuum. The apparatus is also suitable for use in conjunction with large sealed chambers, such as refrigeration units, laboratories, manufacture or assembly areas and the like.
Optionally, the outlet vents to atmospheric pressure.
The fluid compressed by the twin screw compressor may be a gas. The twin screw compressor may be a dry twin screw compressor.
According to a second aspect of the invention, there is provided a method for generating a vacuum across a range of different inlet pressures, the method comprising the steps of:

providing a twin screw compressor, having an inlet communicable with a sealed volume and an outlet for venting exhaust fluid, and a valve member associated with the screw compressor, wherein the valve member is automatically moveable in response to an inlet/outlet pressure differential to vary an outlet volume;
generating a partial vacuum within the sealed chamber by accepting fluid through the inlet, compressing the fluid using the twin screw compressor, venting the compressed fluid through the outlet; and
automatically moving the valve member in response to the inlet/outlet differential pressure and thereby varying the outlet volume.

Optionally, the method includes the step of moving the valve member between an open configuration and a closed configuration.
Optionally, the method includes the step of biasing the valve member into a particular configuration. Optionally, the method includes the step of biasing the valve member into a configuration in which the outlet volume is increased relative to the inlet volume.
Optionally, the method includes the step of providing a biasing means to bias the valve member into a particular configuration. Optionally, the method may include the step of selecting the force of the biasing means to thereby control transition of the valve member between the open and closed configurations in response to the inlet/outlet pressure differential.
Optionally, the method includes the step of damping movement of the valve member in response to the inlet/outlet pressure differential.
According to a third aspect of the invention, there is provided a system for generating a partial vacuum, the system comprising a sealed volume and an apparatus according to the first aspect of the invention.
Optionally, the sealed volume includes, but is not limited to: chambers, factories, industrial process sites, assembly areas, refrigeration units, laboratories, scientific research areas and the like.
Any aspect, feature, embodiment or step of the first, second or third aspects of the invention is equally applicable to any other aspect of the invention, where appropriate.
"Partial vacuum" or "vacuum generation" as used herein is intended to cover any reduction in density of particles per volume, gas concentration and/or pressure within the sealed volume relative to an ambient environment.
"Automatically" as used herein with reference to the apparatus or method is intended to cover any process occurring without the requirement for external intervention.
Further features and advantages of the first and second aspects of the present invention will become apparent from the claims and the following description.
Embodiments of the present invention will now be described by way of example only, with reference to the following diagrams, in which:-

Fig. 1 is an exploded isometric view of one embodiment of an apparatus of the invention;
Fig. 2 is a sectional view of the apparatus of Fig. 1 operating with a high inlet/outlet pressure differential;
Fig. 3 is a sectional view of the apparatus of Fig. 1 operating with a low inlet/outlet pressure differential;
Fig. 4 is a graph showing change of rotor chamber volume with rotation angle; and
Fig. 5 is a perspective view of the apparatus of Fig. 1 with the stator removed.

According to a first embodiment of the invention, an apparatus is shown generally at 10 in Figs. 1 to 3 and 5. The apparatus 10 is operable to generate and maintain a partial vacuum within a sealed volume. The apparatus 10 may be used for a variety of applications to generate and/or maintain a partial vacuum, which include refrigeration and industrial or scientific processes. The apparatus 10 comprises a twin screw compressor 30 and an associated valve and valve actuation means for automatically varying the outlet volume of the twin screw compressor 30.
The compressor 30 comprises twin screws 5 located within a bore 23 of a housing 6. The bore 23 of the housing 6 forms a stator. A first or inlet end of the housing 6 is connected to an inlet portion 22 that incorporates an inlet port 8. In use, the inlet portion 22 is connected to a sealed chamber (not shown) in which the partial vacuum is generated. The inlet 8 port provides fluid communication between the sealed chamber and an inlet end of the twin screws 5. A compressor exhaust face 9 is located at an opposing end of the bore 23 within the housing 6. The compressor exhaust face 9 provides a substantially planar end surface enabling gas delivered by the twin screws 5 in use, to be compressed thereagainst. An outlet port 12 located in the compressor exhaust face 9 leads to a compressor exhaust 7 to provide fluid communication between the outlet end of the twin screw 5 rotors and the exhaust 7. The outlet end of the housing 6 is connected to an end cap 21 of a screw rotor drive assembly 24. The end cap 21 has a radial recess that acts as a compressor discharge chamber 11. The compressor discharge chamber 11 is in fluid communication with the compressor exhaust 7.
The twin screws 5 are two multi-wrap counter rotating variable pitch rotors that each have a parallel axis. The rotors are synchronised and driven by gears located in the end cap 21 of the screw rotor drive assembly 24. The thread pitch of the rotors reduces from the inlet end to the exhaust face 9 of the compressor 30. In use, the variable pitch rotors are arranged to trap working fluid in pockets, which pockets reduce in volume as the rotors rotate. In addition, the volume is further reduced by compressing the working fluid against the compressor exhaust face 9.
A parallel bore 20 is provided along a portion of the bore of the housing 6 towards the exhaust end. The parallel bore 20 accommodates a slide valve 1 that is shaped to locate between a cusp of the twin screw 5 rotors. The slide valve 1 matches the internal profile of the stator and is held against rotation by an anti-rotation device. The slide valve 1 is slidable within the parallel bore 20 between an end stop 25 formed by the housing 6 and the end cap 21. Advantageously, the slide valve 1 does not extend along the length of the twin screw 5 rotors so that there is no direct leak path between the inlet and outlet.
A slide valve actuation means in the form of a piston 2 actuable by differential pressure is used to control movement of the slide valve 1 within the parallel bore 20. The piston 2 is accommodated within a chamber in a sidewall of the housing 6. A first end of the chamber is in fluid communication with a conduit 14 extending axially through a sidewall of the housing 6. The conduit 14 is in fluid communication with the inlet portion 22. A second end of the chamber is located adjacent the parallel bore 20.
The piston 2 is connected to the slide valve 6 via a connecting rod and moveable therewith such that movement of the piston 2 is directly translated to the slide valve 1. The piston 2 is sealed within the chamber, dividing the chamber into a first chamber portion 16 and a second chamber portion 15. The first chamber portion 16 and a first face of the piston 2 are exposed to pressure from the inlet side of the apparatus 10. The second chamber portion 15 and a second opposing face of the piston 2 are exposed to pressure from the exhaust side of the apparatus 10. A biasing means in the form of a spring 3 is positioned between the end stop 25 and the first face of the piston 2. The spring 3 force is selected such that when the differential pressure is below a predetermined value, the spring 3 acts to urge the piston 2 towards the exhaust end of the compressor 30. As a result, the slide valve 1 exposes a length of the twin screw 5 rotors to the exhaust pressure and the slide valve 1 is in a fully open configuration as shown in Figure 3. Therefore the spring 3 preload is set so that the slide valve 1 is normally open when use of the apparatus 10 is initiated according to the present embodiment. In use, when the differential pressure across the piston 2 increases beyond the predetermined value for the spring 3 force, the actuator piston 2 is urged against the spring 3 force causing the slide valve 1 to close as shown in Figure 2.
The differential pressure at which the slide valve 1 transitions between the open and closed positions can be tailored to suit individual applications by changing the spring 3 preload and/or spring 3 rate. A screw adjuster (not shown) allows the initial preload in the spring 3 to be changed. This changes the activation point of the slide valve 1.
A flow restrictor 4 is located within the conduit 14 at one end towards the inlet portion 22. The flow restrictor 4 acts as a choke to limit the flow of working fluid from the inlet portion 22 of the actuator piston 2 thereby limiting the actuating speed of the slide valve 1 to substantially prevent shock loads being transmitted to the piston 2 and slide valve 1 in use.
One embodiment of a method of operation of the apparatus 10 is described below.
When there is a requirement to generate a vacuum within a sealed volume, such as an automated assembly/production area for semiconductors, the apparatus 10 is connected to the sealed volume via the inlet portion 22. Initially the sealed volume is at ambient pressure prior to commencement of the assembly/production of semiconductors. Thus, the differential pressure across the piston 2 is low. The spring 3 preload is therefore the dominant force acting on the piston 2, which adopts an open position to abut the end cap 21 in a direction depicted by an arrow 17. This ensures that the slide valve 1 remains in a bypass condition (or open position) as shown in Fig 3. Whenever the slide valve 1 transitions into the open position, the flow restrictor 4 at the inlet end of the apparatus 10 limits the mass flow of fluid from the inlet side of the actuator piston 2 into the first chamber 16.
The screw rotor drive assembly 24 is actuated to cause rotation of the twin screws 5. Working fluid enters the apparatus 10 via the inlet 8 and is drawn into the twin screw compressor 30. The pitch and interrelation of the twin screw 5 rotors create sealed pockets to transport and compress the working fluid between the rotors and the stator. The clearance between the twin screw 5 rotors and the interior of the housing 6 forming the stator as well as the clearance between each rotor is sufficiently small to create an effective seal between adjacent trapped volumes. The ratio of volume to leakage is sufficiently small that the internal pressure increases when the twin screw 5 rotors are rotated. At high inlet pressures, the open slide valve 1 allows working fluid to flow from the pockets of the twin screw 5 rotors and through the opening depicted by an arrow 18 in Fig. 3. In this way, the working fluid is compressed by the twin screw 5 rotors and vents into the compressor discharge chamber 11 without undergoing additional compression against the compressor exhaust face 9. This reduces the build-up of pressure in the working fluid and therefore reduces power requirements of the apparatus 10.
Continued operation of the apparatus 10 results in withdrawal and compression of the working fluid from the sealed volume as described above. As a result of this process, a partial vacuum is generated in the sealed volume and the pressure within the sealed volume drops. When the sealed volume is at low pressure and the pressure differential across the piston 2 is above the predetermined value, the flow restrictor 4 restricts mass flow against the low-pressure or first face of the piston 2 by choking fluid flow through the conduit 14 thereby damping out any rapid movement of the piston 2 and hence the slide valve 1. Thus, when the differential pressure across the piston 2 increases beyond the preselected value of the spring 3 force, there is a resultant controlled axial force on the piston 2 resulting from the higher pressure differential. Therefore, the piston 2 moves gradually axially and this movement is directly translated to close the slide valve 1 in the position shown in Figure 2.
As a result of the piston 2 closing the slide valve 1, the vent path for working fluid is closed and the full length of the twin screw 5 rotors is used for compression of the working fluid. This allows the working fluid to be compressed along the full length of the twin screw 5 rotors and against the exhaust face 9 of the stator. Reference numeral 19 in Figure 5 shows the compressed volume of working fluid contacting the compressor exhaust face 9. The volume of working fluid trapped between the twin screw 5 variable pitch rotor lobes decreases as the rotors rotate due to the variation in rotor pitch. Continued rotation of the twin screw 5 rotors simultaneously, compresses the trapped volume 19 against the exhaust face 9 resulting in higher internal compression. This is shown in the graph of Figure 4 demonstrating the change of rotor chamber volume on the y-axis with rotation angle on the x-axis. As depicted by an arrow 27 on the graph, screw chamber volume decreases as a result of reducing rotor pitch angle. An arrow 28 points to a portion of the graph where the twin screw 5 chamber volume 26 comes into contact with the exhaust end face 8 to thereby achieve a significant reduction in the volume of working fluid. When the slide valve 1 is in the closed positon as shown in Fig 2, the compressed working fluid exits the apparatus 10 via the outlet 12 and through the exhaust port 7.
As explained in the above description of the operation of the apparatus 10, the valve control or actuation means automatically provides the required actuator force for the slide valve 1 since it is responsive to differential pressure across the apparatus 10 between the inlet and the exhaust. Thus, the valve actuation means advantageously works automatically to move the slide valve 1 without any requirement for a hydraulic actuator or external mechanical assistance. Since the valve actuation means responds directly to inlet and exhaust line conditions there is no requirement for a separate control system.
A further key benefit of the apparatus 10 results from matching the internal compression of the working fluid with the differential pressure across the piston 5 to minimise the power requirements of the twin screw 5 rotors.
The ratio of the trapped inlet volume (v1) to the exhaust volume immediately prior to opening to exhaust (v2) gives the internal volume ratio (Vi) of the compressor: $Vi = v 1 / v 2$
Typically when the inlet pressure of a conventional vacuum compressor is near atmospheric pressure and the inbuilt volume ratio is high Vi >5, the input power can be significantly high. Depending on the efficiencies of the conventional compressor, a theoretical pressure ratio of Vi^Υ will be achieved, where Υ is the ratio of the specific heats of the working fluid at constant pressure and at constant volume. If an inverter drive is used, the rotation speed of the conventional compressor is reduced to limit the power requirement and prevent damage to the compressor bearings. However, reducing the rotation speed of the conventional compressor reduces the compressor capacity and efficiency.
The aforementioned disadvantages of conventional compressors are alleviated by the present apparatus 10. At high inlet pressures the slide valve 1 allows the working fluid to flow from the trapped pockets through the opening generated by the slide valve 1 then through vent holes to the discharge end of the compressor 30. This reduces the build-up of pressure in the working fluid.
According to the present embodiment, the slide valve 1 is of sufficient length from the compressor exhaust face 9 that it lies adjacent the trapped pockets as they start to compress against the exhaust face 9 of the stator. According to alternative embodiments, the slide valve 1 may be positioned to open at different points to vary volume reduction.
According to alternative embodiments, different screw rotors may be used. For example, constant pitch rotors may be used to compress the working fluid against the exhaust face. In another example, the rotors have a complementary profile such that they drive each other. Oil may be injected into the twin screw compressor 30 to lubricate the rotors and the contact areas to cool the working fluid during compression.
Although particular embodiments of the invention have been disclosed herein in detail, this is by way of example and for the purposes of illustration only. The aforementioned embodiments are not intended to be limiting with respect to the scope of the statements of invention and/or the appended claims. Relative terms such as "low" and "high" are illustrative and do not limit the scope of the invention.
It is contemplated by the inventor that various substitutions, alterations, and modifications may be made to the invention without departing from the scope of the invention as defined by the statements of invention and/or the claims.
The present invention may be used for vacuum generation for any application and is not limited to applications listed herein.

Claims

An apparatus (10) for generation of a partial vacuum within a sealed volume, the apparatus (10) comprising:
a twin screw compressor (30), having an inlet (8) communicable with a sealed volume and an outlet, wherein the twin screw compressor (30) is operable to accept fluid through the inlet (8), compress the fluid and vent the compressed fluid through the outlet; and

a valve member (1) associated with the twin screw compressor (30) and movable to vary the outlet volume, wherein the valve member (1) is actuable automatically in response to an inlet/outlet pressure differential.
An apparatus (10) according to claim 1, wherein the valve member (1) is associated with and located in the region of the screw compressor outlet, wherein the valve member (1) is selectively movable to vary the outlet volume and hence change the inlet/outlet volume ratio.
An apparatus (10) according to claim 1 or claim 2, wherein the valve member (1) is moveable between a first configuration in which the outlet volume is minimised and a second configuration in which the outlet volume is increased.
An apparatus (10) according to claim 3, wherein the valve member (1) is movable into the first configuration to reduce the volume of fluid at the outlet at high differential inlet/outlet pressures and movable into the second configuration to increase the volume of fluid at the outlet at a low differential inlet/outlet pressures.
An apparatus (10) according to claim 3 or claim 4, wherein the valve member (1) is arranged to transition between the first and second configurations at a predetermined inlet/outlet pressure.
An apparatus (10) according to any one of claims 3 to 5, wherein the valve member (1) comprises a biasing means to bias the valve into the first configuration in which the outlet volume is increased relative to the inlet volume.
An apparatus (10) according to any preceding claim, wherein the apparatus (10) comprises a valve control mechanism for automatically controlling movement of the valve member (1) based on the differential inlet/outlet pressure, wherein the valve control mechanism is coupled to the valve member (1) such that movement of the valve control system is translated to the valve member (1).
An apparatus (10) according to claim 7, wherein the valve control mechanism comprises a valve actuation member exposed to inlet and outlet pressure, said actuation member being responsive to, and movable by, a differential inlet/outlet pressure of a predetermined value.
An apparatus (10) according to any preceding claim, wherein the apparatus (10) comprises a damping system arranged to substantially restrict application of large forces to the valve member (1).
An apparatus (10) according to claim 9, when dependent on claims 7 and 8, wherein the damping system is associated with the valve control mechanism and comprises a flow restrictor on an inlet side of the valve control mechanism.
A method for generating a vacuum across a range of different inlet pressures, the method comprising the steps of:
providing a twin screw compressor (30), having an inlet communicable with a sealed volume and an outlet for venting exhaust fluid, and a valve member (1) associated with the screw compressor (30), wherein the valve member (1) is automatically moveable in response to an inlet/outlet pressure differential to vary an outlet volume;

generating a partial vacuum within the sealed chamber by accepting fluid through the inlet, compressing the fluid using the twin screw compressor (30), venting the compressed fluid through the outlet; and

automatically moving the valve member (1) in response to the inlet/outlet differential pressure and thereby varying the outlet volume.
A method according to claim 11, wherein the method includes the step of damping movement of the valve member (1) in response to the inlet/outlet pressure differential.
A method according to claim 11 or claim 12, wherein the method includes the step of biasing the valve member (1) into a configuration in which the outlet volume is increased relative to the inlet volume.
A method according to any one of claims 11 to 13, wherein the method includes the steps of:
providing a biasing means to bias the valve member (1) into a particular configuration; and

selecting the force of the biasing means and thereby modifying movement of the valve in response to a specific predetermined inlet/outlet pressure differential.
A system for generating a partial vacuum, the system comprising a sealed volume and an apparatus according to any one of claims 1 to 10.