GB2618353A

GB2618353A - Rotor assembly

Info

Publication number: GB2618353A
Application number: GB2206531.2A
Authority: GB
Inventors: Meeusen Wim; Van Hoof Nils; Antoine J Cools Ronny; Anna Victor Michiels Emma; Verreth Annelies; Wybaillie Gauthier; Van Steenlandt Jan; Maes Jordy
Original assignee: Atlas Copco Airpower NV
Current assignee: Atlas Copco Airpower NV
Priority date: 2022-05-05
Filing date: 2022-05-05
Publication date: 2023-11-08
Also published as: WO2023214021A1

Abstract

A rotor assembly comprising a rotor 104 having a screw-type body portion, where the screw-type body portion comprises lobes that define inter-lobe volumes and where there are multiple valves 126 (e.g. non-return valves) such that each valve is in fluid communication with a respective inter-lobe volume and configured to control a flow of fluid out of said respective inter-lobe volume. Preferably the valves are coupled to an end of the rotor. The rotor assembly may also comprise valve seats 132 between the rotor and the valves, where the valve seats may be provided by a valve seat plate between an end of the rotor and the valves and where the seat plate may have a openings therethrough such that each opening is in fluid communication with an inter-lobe volume and such that each opening can be controllably sealed by a valve. An apparatus 100, such as a compressor, expander, or vacuum pump, having the claimed rotor assembly is also claimed. A valve assembly 112 is also claimed.

Description

ROTOR ASSEMBLY

FIELD OF THE INVENTION

The present invention relates to rotor assemblies, such as those for 5 screw-type compressors, expanders and vacuum pumps, and also to screw-type compressors, expanders and vacuum pumps.

BACKGROUND

In screw-type compressors, intermeshed male and female lobed rotors or screws are rotated about their respective axes to pump fluid between an inlet port of the compressor at a low-pressure inlet end and an outlet port of the compressor at a high-pressure outlet end.

During rotation of the rotors, sequential lobes of the male rotor drive fluid downstream and compress it within the space between adjacent pairs of female rotor lobes and the housing. Similarly, sequential lobes of the female rotor compress the liquid between adjacent pairs of male rotor lobes and the housing.

During operation of the compressor, when an inter-lobe volume of a rotor is exposed to the inlet port, fluid enters that inter-lobe volume at suction pressure. Rotation of the rotors cause the inter-lobe volume to displace. At some point during its rotation, the inter-lobe volume is no longer in communication with the inlet port. Thus, the flow of fluid into the inter-lobe volume is prevented. After the inter-lobe volume is closed, the fluid therein is compressed as the rotors continue to rotate and the volume of the inter-lobe volume is reduced. At some point during the rotation of the rotors, the inter-lobe volume is brought into fluid communication with the outlet port. At this stage, the compression of the fluid in the inter-lobe volume ends and the compressed fluid exits the compressor via the outlet.

SUMMARY OF THE INVENTION -2 -

The present inventors have realised that conventional screw-type compressors are susceptible to over-compression and/or under-compression. The present inventors have further realised that valves may be implemented to reduce or eliminate the risk of over-compression and/or under-compression.

Reduction or elimination of the risk of over-compression and/or under-compression tends to improve the compressor efficiency.

In a first aspect, there is provided a rotor assembly comprising: a rotor comprising a screw-type body portion, the screw-type body portion comprising a plurality of lobes, the lobes of the plurality of lobes defining a plurality of inter-lobe volumes between said lobes; and a plurality of valves, each valve of the plurality of valves being in fluid communication with a respective inter-lobe volume of the plurality of inter-lobe volumes and configured to control a flow of fluid out of said respective inter-lobe volume.

The plurality of valves may be coupled to an end of said rotor.

The rotor assembly may further comprise a plurality of valve seats disposed between the rotor and the plurality of valves, wherein each valve of the plurality of valves is configured to seal against a respective valve seat of the plurality of valve seats.

The plurality of valve seats may be provided by a valve seat plate disposed between an end of the rotor and the plurality of valves. The valve seat plate may comprise a plurality of openings therethrough. Each opening of the plurality of openings may be in fluid communication with a respective inter-lobe volume. Each opening of the plurality of openings may be configured to be controllably sealed by a respective valve of the plurality of valves.

Each valve of the plurality of valves may be a non-return valve.

Each valve of the plurality of valves may be a reed valve.

The rotor assembly may further comprise a plurality of valve limiters. Each valve limiter of the plurality of valve limiters may be configured to limit an extent to which a respective valve of the plurality of valves is able to open. -3 -

Each valve of the plurality of valves may be configured to rotate or bend about a respective hinge axis. The hinge axes of one or more of the valves may be substantially parallel to a direction that is tangential to the rotor.

Each valve of the plurality of valves may be configured to rotate or bend 5 about a respective hinge axis. The hinge axes of one or more of the valves may be substantially parallel to a radial direction of the rotor.

Each valve of the plurality of valves may be configured to rotate or bend about a respective hinge axis. The hinge axes of one or more of the valves may be substantially oblique to both a direction that is tangential to the rotor and a radial direction of the rotor.

The rotor may be a male rotor. The rotor may be a female rotor.

In a further aspect, there is provided an apparatus, the apparatus being a compressor, an expander, or a vacuum pump. The apparatus comprises: a housing defining an inlet and an outlet; and a rotor assembly according to any preceding aspect. The rotor assembly is housed within said housing between the inlet and outlet.

The apparatus may further comprise a further rotor comprising a further screw-type body portion, the further screw-type body portion being enmeshed with the screw-type body portion of the rotor.

The housing may further comprise an access port through which one or more of the valves of the plurality of valves are accessible.

In a further aspect, there is provided a valve assembly comprising: a central body configured to be fitted to a rotor shaft of a compressor, an expander, or a vacuum pump; and a plurality of valves coupled to the central body, each valve having a different respective radial position about the central body.

Each valve of the plurality of valves may be a reed valve The valve assembly may further comprise a valve seat plate. The valve seat plate may have a fixed position relative to the central body. The valve seat -4 -plate may define a plurality of valve seats. Each valve of the plurality of valves may be configured to seal against a respective valve seat of the plurality of valve seats. The valve seat plate may comprise a plurality of openings therethrough. Each opening of the plurality of openings may be configured to be controllably sealed by a respective valve of the plurality of valves.

Each valve of the plurality of valves may be configured to rotate or bend about a respective hinge axis. The hinge axes of one or more of the valves may be substantially parallel to a direction that is tangential to the central body. The hinge axes of one or more of the valves may be substantially parallel to a radial direction of the central body. The hinge axes of one or more of the valves may be substantially oblique to both a direction that is tangential to the central body and a radial direction of the central body.

The valve assembly may further comprise a plurality of valve limiters. Each valve limiter of the plurality of valve limiters may be configured to limit an extent to which a respective valve of the plurality of valves is able to open.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic illustration (not to scale) of a side view cross section of a compressor; Figure 2 is a schematic illustration (not to scale) of a top view cross section of a part of the compressor.

Figures 3 and 4 are schematic illustrations (not to scale) showing certain elements of a valve assembly of the compressor; and Figures 5 to 8 are schematic illustrations (not to scale) showing certain elements of further valve assemblies.

DETAILED DESCRIPTION

It will be appreciated that relative terms such as above and below, horizontal and vertical, top and bottom, front and back, and so on, are used -5 -herein merely for ease of reference to the Figures, and these terms are not limiting as such, and any two differing directions or positions and so on may be implemented rather than truly above and below, horizontal and vertical, top and bottom, and so on Figure 1 is a schematic illustration (not to scale) of a side view cross section of an embodiment of a compressor 100.

Figure 2 is a schematic illustration (not to scale) of a top view cross section of a part of the compressor 100.

In this embodiment the compressor comprises a housing 102, a first rotor 1() 104, a first shaft 106, a second rotor 108, a second shaft 110, a valve assembly 112, and a motor 114.

The housing 102 comprises an inlet port 116 located at or proximate to a first end of the housing 102. In this embodiment, the inlet port 116 is a radial port, i.e. the inlet port is oriented in the radial direction which is perpendicular to a longitudinal axis of the compressor 100. However, in other embodiments, the inlet port 116 may be an axial port or a combination of an axial port and a radial port.

The housing 102 further comprises an outlet port 118 located at or proximate to a second end of the housing 102 opposite to the first end of the housing 102. In this embodiment, the outlet port 118 is a radial port. However, in other embodiments, the outlet port 118 may be an axial port or a combination of an axial port and a radial port The first shaft 106 extends through the housing 102 from the first end of the housing to the second end of the housing 102. The first shaft 106 is rotatably mounted to the housing 102 via one or more bearing assemblies (not shown). The first shaft 106 is configured to rotate with respect to the housing 102 about a first axis 120.

In this embodiment, the first rotor 104 is a screw-type rotor comprising a first end, a second end opposite to the first end, and a screw-type body or 30 working portion extending between the first and second ends. The first rotor 104 -6 -is a female screw-type rotor. Thus, the screw-type body portion of the first rotor 104 is a female-lobed body or working portion. In this embodiment, the first rotor 104 comprises six helical lobes. Further details of the first rotor are described in more detail later below with reference to Figures 3 and 4.

The first rotor 104 is fixedly mounted to the first shaft 106. The first rotor 104 may be unitarily formed with the first shaft 106. The first rotor 104 is housed within an internal chamber 122 of the housing 102 between the inlet port 116 and the outlet port 118. In particular, in this embodiment, the first end of the first rotor 104 is located at or proximate to the inlet port 116. Also, the second end of to the first rotor 104 is located downstream of the first end, between the inlet port 116 and the outlet port 118 and preferably proximate to the outlet port 118.

The second shaft 110 extends through the housing 102 from the first end of the housing to the second end of the housing 102. The second shaft 110 is rotatably mounted to the housing 102 via one or more bearing assemblies (not shown). The second shaft 110 is configured to rotate with respect to the housing 102 about a second axis 124.

In this embodiment, the second rotor 108 is a screw-type rotor comprising a first end, a second end opposite to the first end, and a screw-type body or working portion extending between the first and second ends. The second rotor 108 is a male rotor. Thus, the screw-type body portion of the second rotor 108 is a male-lobed body or working portion. In this embodiment, the second rotor 108 comprises four helical lobes.

The second rotor 108 is fixedly mounted to the second shaft 110. The second rotor 108 may be unitarily formed with the second shaft 110. The second rotor 108 is housed within the chamber 122 of the housing 102 between the inlet port 116 and the outlet port 118. In particular, in this embodiment, the first end of the second rotor 108 is located at or proximate to the inlet port 116. Also, the second end of the second rotor 108 is located downstream of the first end, between the inlet port 116 and the outlet port 118 and preferably proximate to the outlet port 118. -7 -

In this embodiment, the female-lobed body portion of the first rotor 104 is enmeshed with the male-lobed body portion of the second rotor 108. In other words, the lobes of the first rotor 104 are enmeshed with the lobes of the second rotor 108 The valve assembly 112 is coupled to the first rotor 104. More specifically, the valve assembly 112 is attached to the second end of the first rotor 104. The valve assembly 112 is positioned around the first shaft 106. Thus, the valve assembly 112 is located between the first rotor 104 and the outlet port 118 In this embodiment, the valve assembly 112 comprises a plurality of valves 126 which are hingedly attached via hinges 128 to a fixed element 130. The fixed element 130 is fixedly attached around the first shaft 106. In some embodiments, the fixed element 130 is integral or unitary with the first shaft 106. The fixed element 130 may be considered to be a central body of the valve assembly 112. The valves 126 are non-return valves, i.e. check valves. The valves 126 are configured to control the flow of fluid from the second end of the first rotor 104 to the outlet port 118. The valve assembly 112 further comprises a plurality of valve seats 132 against which the valves 126 are configured to sealingly engage. In this embodiment, the valve assembly 112 further comprises a valve assembly housing 134 which houses the other components of the valve assembly 112. The valve seats 132 may be fixedly attached to the valve assembly housing 134. The valve seats 132 and valve assembly housing 134 are fixed relative to the first shaft 106 and the first rotor 104. For example, the valve seats 132 and valve assembly housing 134 may be fixedly attached to the first shaft 106 and/or the first rotor 104. The valve assembly 112 and its functionality is described in more detail later below with reference to Figures 3 and 4.

In this embodiment, the compressor 100 is an oil-injected compressor. In particular, oil is injected into the compressor 100 during operation from an oil source (not shown). -8 -

The injected oil tends to provide improved sealing between the first and second rotors 104, 108 at points where the first and second rotors 104, 108 touch, thereby to reduce or eliminate backflow of fluid. The injected oil also tends to provide improved sealing between the rotors 104, 108 and the housing 102, thereby to reduce or eliminate backflow of fluid. The injected oil also tends to provide improved sealing between the valves 126 and the valve seat 132, thereby reducing or eliminating backflow of fluid therethrough.

The injected oil tends to provide improved sealing between the valve assembly 112 and the housing 102, thereby to reduce or eliminate backflow of fluid. In particular, the oil tends to provide a seal between the valve assembly housing 134 and the housing 102. In this embodiment the housing 102 comprises an annular groove 136 which surrounds the valve assembly housing 134. This annular groove 136 may be filled with the oil thereby to provide a seal. In some embodiments, other sealing and/or mounting elements, such as a bearing assembly, may be disposed in the annular groove 136 thereby to rotatably support the valve assembly 112 with respect to the housing 102 and/or provide sealing between the housing 102 and the valve assembly 112.

In some embodiment, a different type of sealing mechanism is used instead of or in additional to the annular groove 136, such as a sealing mechanism in which an axial gap is used instead of or in addition to the annular groove.

The injected oil also tends to provide cooling, lubrication, and noise dissipation.

The motor 114 may be an electric motor. In this embodiment, the second rotor 108 is coaxial with the motor 114 and is supported by bearings on inlet and outlet sides of its screw-type body portion. In this embodiment, the motor 114 is configured to drive, i.e. rotate, the second shaft 110 about the second axis 124. When so driven in an operative first direction about the second axis 124, the second rotor 108 drives the first rotor 104 about the first axis 120 in a second direction which may be opposite to the first direction. This enmeshed rotation of the screw-type body portions of the rotors 104, 108 draws fluid into -g -the inlet port 116 (as indicated in Figure 1 by an arrow marked by the reference numeral 138). Preferably, the inlet port geometry is such that the flow of fluid is cut off at the time in the cycle when the volume in which fluid is received reaches its maximum value. After drawing fluid into the inlet port 116, the continued rotation of the rotors 104, 108 drives the fluid through the chamber 122 (as indicated in Figure 1 by an arrow marked by the reference numeral 140) in which the fluid is compressed, causes the fluid to flow through the valves 126 of the valve assembly 112 (as indicated in Figure 1 by arrows marked by the reference numeral 142) which control said fluid flow therethrough, and then causes the compressed fluid to flow out of the outlet port 118 (as indicated in Figure 1 by an arrow marked by the reference numeral 144).

What will now be described with reference to Figures 3 and 4 are further details of the valve assembly 112 and its functionality.

Figures 3 and 4 are schematic illustrations (not to scale) showing in 15 further detail certain elements of the valve assembly 112 attached to the second end of the first rotor 104.

In this embodiment, the first rotor 104 comprises six lobes 300. The lobes 300 are helical lobes. The lobes 300 of the first rotor 104 define inter-lobe volumes 302 between adjacent pairs of the lobes 300.

In this embodiment, each of the valves 126 of the valve assembly 112 is in fluid communication with a respective inter-lobe volume 302. Each valve 126 is configured to control a flow of fluid out of its associated respective inter-lobe volume 302.

In more detail, in this embodiment, the valve seats 132 are provided by a valve seat plate 304. The valve seat plate 304 is a thin, substantially cylindrical plate of a preferably lightweight and strong material, e.g. a metal. Preferably, the valve seat plate 304 is relatively thin or recessed at the location of the valve seats 132, e.g. compared to other parts of the valve seat plate 304. This advantageously tends to minimise the volume of the valve system. The valves 126 can be shaped to fill recesses in the valve seat plate 304. Preferably, the thickness of the valve seat plate 304 is less than or equal to about 1mm.

-10 -Preferably, the diameter valve seat plate 304 is approximately equal to or slightly little larger than that of the rotor (for example, which may be about 10 mm in some embodiments).

The valve seat plate 304 is fixedly attached to the second end of the first rotor 104. The valve seat plate 304 is fixed to and coaxial with the first shaft 106. The valve seat plate 304 comprises a plurality of openings 306. In this embodiment, there are six openings 306. The valve seat plate 304 is fixed to the first rotor 104 such that each of the openings 306 is aligned with a respective inter-lobe volume 302. In this embodiment, each opening 306 is aligned with only one respective inter-lobe volume 302. The material of the valve seat plate 304 that surrounds each of the openings 306 forms a respective valve seat 132 for a respective one of the valves 126.

Each valve 126 is configured to controllably or selectably seal or close a respective opening 306 of the valve seat plate 304. In some embodiments, a valve 126 may seal or close multiple openings 306.

In more detail, each valve 126 is configured to move between an open position and a closed position.

In its closed position, each valve 126 seals against its respective valve seat 132, thereby closing or sealing the opening 306 that is surrounded by that valve seat 132. Thus, fluid flow through the opening 306 is prevented or opposed. Thus, in its closed position, each valve 126 prevents or opposes fluid flow out of a respective inter-lobe volume 302 towards the outlet port 118.

In its open position, each valve 126 has been rotated about its hinge 128 and is moved away from its respective valve seat 132. Thus, the opening 306 surrounded by that valve seat 132 is not closed or sealed and fluid may flow through the opening 306. Thus, in its open position, each valve 126 allows for the fluid to flow out of a respective inter-lobe volume 302 towards the outlet port 118.

In this embodiment, the axes of the hinges 128 (i.e. hinge axes) of the valves 126 are substantially parallel to a direction that is tangential to the first rotor 104. The hinge axes are perpendicular to the first axis 120.

In this embodiment, the cracking pressures of the valves 126 are substantially the same as each other. The cracking pressures of the valves 126 may be application dependent. The cracking pressures of the valves 126 may be defined based on a desired output pressure of the compressor 100 and/or a desired volumetric index or ratio of the compressor 100. The cracking pressures of the valves 126 may be determined using any appropriate methodology, such as computer modelling, or experimentation.

The cracking pressure may be determined dependent on one or more parameters selected from the group of parameters consisting of pressure difference over the valves, rotation speed, hinge location, hinge orientation, valve mass, valve centre-of-gravity, and friction in the valve system. These parameters can be varied or controlled (e.g. optimized) depending on application, i.e. for each pump. In some embodiments, an additional biasing means, such as a spring which may be a rotational spring, can be implemented to fine-tune the valve cracking pressure.

The opening and/or closing speed of the valves may be determined by one or more parameters selected from the group of parameters consisting of valve geometry, valve mass, valve centre of gravity, hinge location, hinge orientation, rotation speed, and friction in the system. The opening and/or closing speed of the valves may be tuned by any appropriate means, for example by provision of a spring.

In operation, when the pressure differential across a valve 126 (i.e. the difference in pressure between the associated inter-lobe volume 302 and the pressure at the outlet port 118) equals or exceeds the valve cracking pressure, the valve 126 is rotated about its hinge 128 to its open position, and fluid flows from the associated inter-lobe volume 302 towards the outlet port 118. Similarly, when the pressure differential across a valve 126 is less than the valve cracking pressure, the valve 126 is rotated about its hinge 128 to its closed position, and fluid is prevented or opposed from flowing out of the associated inter-lobe volume 302.

-12 -In this embodiment, each valve 126 is separately attached to the fixed element 130 by a respective plurality of fasteners 308. Thus, each valve 126 is independently removable from the valve assembly 112, for example for maintenance, repair, servicing, or inspection purposes.

Preferably, the housing 102 comprises an access port through which one or more of the valves 126 are accessible. For example, a valve 126 may be accessed via the access port of the housing. That valve 126 may be detached from the fixed element 130 by releasing its fasteners 308. That valve 126 may then be removed from the compressor 100 via the access port, e.g. for the purpose of maintenance, repair, servicing, or inspection. The valve 126, or a new/replacement valve, may be inserted into the compressor 100 through the access port and attached to the fixed element 130 using the fasteners 308 (or other fixation means). Other valves 126 of the valve assembly 112 may be accessed via the access port by rotating the first shaft 106 to positions where those other valves are accessible through the access port.

Thus, an embodiment of a rotor assembly comprising a rotor and a valve assembly attached thereto is provided. The rotor comprises a screw-type body portion comprising a plurality of lobes. The lobes define a plurality of inter-lobe volumes therebetween. The valve assembly comprises a plurality of valves, each valve being in fluid communication with a respective inter-lobe volume and configured to control a flow of fluid out of that respective inter-lobe volume.

Advantageously, this operation of the valves 126 and the appropriate selection of the valve cracking pressures tends to reduce or eliminate both over-compression and under-compression of the fluid by the compressor 100. Thus, 25 the efficiency of the compressor 100 tends to be improved.

This tends to be beneficial when the inlet pressure or outlet pressure in the pump is not fixed, and also for vacuum pumps which cycle and/or for applications where the pump compression ratio is not equal to a desired compression ratio for the pumping application.

-13 -Advantageously, the above-described rotor assembly tends to provide for fewer and/or lower-amplitude pulsations. This tends to provide for lower vibration and noise levels.

Advantageously, the components of the valve assembly 112 being made of lightweight material, such as the valve seat plate 304 being a thin, lightweight member, tends to reduce centrifugal forces within the compressor 100, including those exerted on the valve assembly 112. This advantageously tends to reduce the likelihood of breakage and damage during use.

The above-described systems advantageously tend to allow for larger outlet channel, compared to conventional outlet ports. This tends to lower flow losses in the outlet system and consequently increase overall efficiency.

In the above embodiments, the rotor assembly is implemented in a compressor, in particular a screw-type compressor. However, in other embodiments, the rotor assembly is implemented in a different system or 15 apparatus, such as an expander or a vacuum pump.

In the above embodiments, the compressor is an oil-injected compressor. However, in other embodiments the apparatus is not oil-injected. For example, the apparatus may be a so-called "dry" compressor, expander, or vacuum pump. In some embodiments, the compressor may be injected with a different type of lubricating and/or sealing fluid instead of or in addition to oil, such as water.

In the above embodiments, the compressor comprises two rotors, namely the first and second rotors. However, in other embodiments, the apparatus comprises a different number of rotors, such as more than two rotors.

For example, in some embodiments, there may be multiple female rotors engaged to a given male rotor or vice versa.

In the above embodiments, the compressor comprises a single inlet port. However, in other embodiments the apparatus comprises a different number of inlet ports, i.e. more than one inlet port.

-14 -In the above embodiments, the compressor comprises a single outlet port. However, in other embodiments the apparatus comprises a different number of outlet ports, i.e. more than one outlet port.

In the above embodiments, the first rotor is a female rotor and the second rotor is a male rotor. However, in other embodiments the first rotor is a male rotor and the second rotor is a female rotor.

In the above embodiments, the first rotor is a six-lobed rotor. However, in other embodiments, the first rotor has a different number of lobes, for example 3, 4, 5, 7, 8, 9, 10, or more than 10 lobes.

In the above embodiments, the second rotor is a four-lobed rotor.

However, in other embodiments, the second rotor has a different number of lobes, for example 3, 4, 5, 6, 7, 8, 9, 10, or more than 10 lobes.

In the above embodiments, the second rotor drives the first rotor. However, in other embodiments, the second rotor does not drive the first rotor.

For example, in some embodiments the first rotor drives the second rotor. In such embodiments, the first rotor may be driven by a motor. In some embodiments, the first and second rotors are separately driven by respective motors or a common motor. In such embodiments, the first and second rotors may be spaced apart such that they do not contact each other in operation.

The motor or motors can be coupled to either or both of the male or female rotors, and on either or both of the inlet or outlet sides of the rotor(s). The motor or motors can be coupled by a mechanical coupling or may be directly coupled to a rotor shaft In the above embodiments, the valve assembly comprises six valves.

However, in other embodiments, the valve assembly comprises a different number of valves, for example 3, 4, 5, 6, 7, 8, 9, 10, or more than 10 valves.

In the above embodiments, each valve is separately attached to the fixed element by a respective plurality of fasteners. However, in other embodiments one or more of the valves is not attached to the fixed element by a respective plurality of fasteners. For example, in some embodiments, one or more of the -15 -valves may be integrally formed with the fixed element. For example, one or more of the valves may be a reed valve such as those described in more detail later below with respect to Figures 5 and 8.

In the above embodiments, the hinge axes about which the valves are configured to rotate are substantially parallel to a direction that is tangential to the first rotor. However, in other embodiments one or more of the hinge axes are not parallel to a direction that is tangential to the first rotor. For example, in some embodiments, the hinge axes of one or more of the valves is aligned along a radial direction. In some embodiments, the hinge axes of one or more of the valves is substantially parallel to a radial direction of the first rotor. In some embodiments, the hinge axes of one or more of the valves is oblique to a direction that is tangential to the first rotor and/or a radial direction of the first rotor.

In the above embodiments, the valves seats are provided by a valve seat plate attached to an end of the first rotor. However, in other embodiments, the valve seat plate may be omitted and/or the valve seats may be provided by a different structure other than a valve seat plate. For example, in some embodiments, the end of the rotor itself defines or provides the valves seats and the valves may be configured to seal against the end surface of the rotor.

In some embodiments, the valve assembly further comprises one or more valve limiters. Each valve limiter may be configured to limit an extent to which a respective valve of the valve assembly is able to open.

The valve limiters advantageously tend to prevent over-opening of valves. This may prevent or reduce the likelihood of the valves contacting static parts of the compressor. This damage to the valves and/or other parts of the compressor may be reduced or limited. There tends to be limited space for the valves and the valves tend to be located in the vicinity of the bearings and bearing housing. Use of the limiters tends to limit valve movement to within a desired volume.

-16 -The limiters advantageously tend to prevent or reduce the likelihood of reed valves being over-extended and of local stress concentration causing failure.

What will now being described with reference to Figure 5 to 7 is a plurality of other exemplary embodiments of the rotor assembly.

Figure 5 is a schematic illustration (not to scale) showing in certain elements of a further embodiment of a rotor assembly.

In this embodiment, the valves 126 are reed valves. The valves 126 comprise flexible flaps or sheets of material, such as flexible metal or composite materials. The valves may be formed of thin material, for example material having a thickness of 0.1 mm to 0.5 mm, or more preferably 0.15 mm to 0.25 mm. The valves 126 are configured to open and close the openings 306 depending on the pressure differential across the valves 126. (The valves 126 are shown in their closed positions in Figure 5.) In this embodiment, the end surface of the first rotor defines the valve seats 132. The reed valves 126 are configured to sealingly engage with the end surface of the first rotor 104 thereby to close or seal the openings 306. Thus, in this embodiment, the valve seat plate 304 is omitted.

In this embodiment, the valve assembly 112 further comprises a plurality of valve limiters 500. Specifically, the valve assembly 112 comprises six valve limiters 500. Each valve limiter 500 is configured to limit an extent to which a respective reed valve 126 is able to open. In this embodiment, the valve limiters 500 are integrally formed. The valve limiters 500 are fixedly attached to the first rotor 104.

Each valve 126 is configured to rotate or bend about a respective hinge axis 502. Each hinge axis 502 is substantially parallel to a respective direction that is tangential to the first rotor 104.

Advantageously, the reed valves 126 tends to have a relatively simple construction.

-17 -The reed valves 126 tends to be relatively lightweight. This tends to reduce centrifugal forces acting on the reed valves 126, thereby reducing the likelihood of breakage and damage during use.

Advantageously, the reed valves 126 tend to reduce or eliminate a need 5 for valve hinges. This tends to reduce maintenance time and/or period between maintenance being performed.

Figure 6 is a schematic illustration (not to scale) showing in certain elements of a second further embodiment of a rotor assembly.

The valve assembly 112 comprises a plurality of valves 126 which are hingedly attached via hinges 128 to the fixed element 130. In this embodiment, the hinges 128 are aligned along respective radial directions with respect to the first axis 120/first rotor 104. In other words, the hinge axes 600 about which the valves 126 rotate are aligned along (or may be parallel with in some embodiments) radial directions of the first rotor 104.

Advantageously, the radial hinging of the valves 126 tends to reduce a risk of the valves being forced closed by centrifugal forces acting on the valves 126.

Figure 7 is a schematic illustration (not to scale) showing in certain elements of a third further embodiment of a rotor assembly.

The valve assembly 112 comprises a plurality of valves 126 which are hingedly attached via hinges 128 to the fixed element 130. In this embodiment, the hinges 128 are aligned along respective directions which are oblique to radial directions with respect to the first axis 120/first rotor 104. The hinge axes 700 about which the valves 126 rotate are aligned along directions which are oblique to both a direction that is tangential to the first rotor 104 and a radial direction of the first rotor 104. More specifically, each hinge axis 700 is at an angle a with respect to a respective radial direction 702 of between -10° and 20°, or more preferably between 5° and 20°. More preferably, the angle a is between 100 and 150. The angle a may depends on the number of valves, valve geometry, the valve centre-of-gravity, and/or the desired crack pressure.

-18 -Advantageously, the oblique hinging of the valves 126 tends to reduce a risk of the valves being forced closed by centrifugal forces acting on the valves 126.

Figure 8 is a schematic illustration (not to scale) showing in certain elements of a fourth further embodiment of a rotor assembly.

In this embodiment, the valves 126 are reed valves. The valves 126 comprise flexible flaps or sheets of material, such as flexible metal or composite materials. The valves may be formed of thin material, for example material having a thickness of 0.1 mm to 0.5 mm, or more preferably 0.2 mm to 0.3 mm.

to The valves 126 are configured to open and close the openings 306 depending on the pressure differential across the valves 126. The valves 126 are indicated using hatching in Figure 8.

In this embodiment, a valve seat plate may be implemented, or may be omitted. The end surface of the first rotor may define the valve seats 132.

In this embodiment, the valve assembly 112 further comprises a plurality of valve limiters 800. Specifically, the valve assembly 112 comprises six valve limiters 800. Each valve limiter 800 is configured to limit an extent to which a respective reed valve 126 is able to open. In this embodiment, the valve limiters 800 are integrally formed. The valve limiters 800 are fixedly attached to the first rotor 104.

Each valve 126 is configured to rotate or bend about a respective hinge axis 802. In this embodiment, each hinge axis 802 may be aligned along a respective direction which is oblique to a radial direction with respect to the first axis 120/first rotor 104. The hinge axes 802 about which the valves 126 bend or rotate may be aligned along directions which are oblique to both a direction that is tangential to the first rotor 104 and a radial direction of the first rotor 104. More specifically, each hinge axis 802 may be at an angle with respect to a respective radial direction 702 of between 5° and 20°. More preferably, the angle may be between 10° and 15°.

Alternatively, in this embodiment, the hinge axes 802 may be aligned along or may be parallel with radial directions of the first rotor 104.

-19 -Advantageously, the reed valves 126 tends to have a relatively simple construction.

The reed valves 126 tends to be relatively lightweight. This tends to reduce centrifugal forces acting on the reed valve 126, thereby reducing the likelihood of breakage and damage during use.

Advantageously, the oblique hinging of the reed valves 126 tends to reduce a risk of the valves being forced closed by centrifugal forces acting on the valves 126 Advantageously, the oblique hinging of the reed valves 126 tends to to reduce a risk of fluttering of the reed valves.

-20 -Reference numerals -compressor 102-housing 104 -first rotor 106 -first shaft 108 -second rotor 110 -second shaft 112 -valve assembly 114-motor 116 -inlet port 118 -outlet port -first axis 122 -internal chamber 124 -second axis 126 -valves 128-hinges -fixed element 132 -valve seats 134 -valve assembly housing 136 -annular groove 138, 140, 142, 144 -fluid flow directions 300 -lobes 302 -inter-lobe volumes 304 -valve seat plate 306 -openings 308 -fasteners 500, 800 -valve limiters 502, 700 -hinge axes 702, 802 -radial directions S a -angle -22 -

Claims

CLAIMS1. A rotor assembly comprising: a rotor comprising a screw-type body portion, the screw-type body portion comprising a plurality of lobes, the lobes of the plurality of lobes defining a plurality of inter-lobe volumes between said lobes; and a plurality of valves, each valve of the plurality of valves being in fluid communication with a respective inter-lobe volume of the plurality of inter-lobe volumes and configured to control a flow of fluid out of said respective inter-lobe volume.
2. The rotor assembly of claim 1, wherein the plurality of valves is coupled to an end of said rotor.
3. The rotor assembly of claim 1 or 2, further comprising a plurality of valve seats disposed between the rotor and the plurality of valves, wherein each valve of the plurality of valves is configured to seal against a respective valve seat of the plurality of valve seats.
4. The rotor assembly of claim 3, wherein: the plurality of valve seats is provided by a valve seat plate disposed between an end of the rotor and the plurality of valves; the valve seat plate comprises a plurality of openings therethrough; each opening of the plurality of openings is in fluid communication with a respective inter-lobe volume; and each opening of the plurality of openings is configured to be controllably sealed by a respective valve of the plurality of valves.
5. The rotor assembly of any preceding claim, wherein each valve of the plurality of valves is a non-return valve.
6. The rotor assembly of any preceding claim, wherein each valve of the plurality of valves is a reed valve.
7. The rotor assembly of any preceding claim, further comprising a plurality of valve limiters, wherein each valve limiter of the plurality of valve limiters is configured to limit an extent to which a respective valve of the plurality of valves is able to open.
8. The rotor assembly of any preceding claim, wherein: each valve of the plurality of valves is configured to rotate or bend about a respective hinge axis; and the hinge axes of one or more of the valves are substantially parallel to a direction that is tangential to the rotor.
9. The rotor assembly of any preceding claim, wherein: each valve of the plurality of valves is configured to rotate or bend about a respective hinge axis; and the hinge axes of one or more of the valves are substantially parallel to a radial direction of the rotor.
10. The rotor assembly of any preceding claim, wherein: each valve of the plurality of valves is configured to rotate or bend about a respective hinge axis; and the hinge axes of one or more of the valves are substantially oblique to both a direction that is tangential to the rotor and a radial direction of the rotor. -24 -
11. The rotor assembly of any preceding claim, wherein the rotor is a male rotor.
12. The rotor assembly of any of claims 1 to 10, wherein the rotor is a female rotor.
13. An apparatus, the apparatus being a compressor, an expander, or a vacuum pump, the apparatus comprising: a housing defining an inlet and an outlet; and a rotor assembly according to any preceding claim, the rotor assembly being housed within said housing between the inlet and outlet.
14. The apparatus of claim 13, further comprising a further rotor comprising a 15 further screw-type body portion, the further screw-type body portion being enmeshed with the screw-type body portion of the rotor.
15. The apparatus of claim 13 or 14, wherein the housing further comprises an access port through which one or more of the valves of the plurality of valves are accessible.
16. A valve assembly comprising: a central body configured to be fitted to a shaft of a compressor, an expander, or a vacuum pump; and a plurality of valves coupled to the central body, each valve having a different respective radial position about the central body.
17. The valve assembly of any claim 16, wherein each valve of the plurality of valves is a reed valve.
18. The valve assembly of claim 16 or 17, further comprising a valve seat plate, wherein the valve seat plate has a fixed position relative to the central body; the valve seat plate defines a plurality of valve seats, each valve of the plurality of valves being configured to seal against a respective valve seat of the plurality of valve seats; the valve seat plate comprises a plurality of openings therethrough; and each opening of the plurality of openings is configured to be controllably sealed by a respective valve of the plurality of valves.
19. The valve assembly of any of claims 16 to 18, wherein: each valve of the plurality of valves is configured to rotate or bend about a respective hinge axis; and either: the hinge axes of one or more of the valves are substantially parallel to a direction that is tangential to the central body; or the hinge axes of one or more of the valves are substantially parallel to a radial direction of the central body; or the hinge axes of one or more of the valves are substantially oblique to both a direction that is tangential to the central body and a radial direction of the central body.
20. The valve assembly of any of claims 16 to 19, further comprising a plurality of valve limiters, wherein each valve limiter of the plurality of valve limiters is configured to limit an extent to which a respective valve of the plurality of valves is able to open.