EP3571407A2

EP3571407A2 - Multi-stage vacuum booster pump coupling

Info

Publication number: EP3571407A2
Application number: EP18734869.3A
Authority: EP
Inventors: Michael Henry North; Nigel Paul Schofield
Original assignee: Edwards Ltd
Current assignee: Edwards Ltd
Priority date: 2017-01-20
Filing date: 2018-01-18
Publication date: 2019-11-27
Also published as: CN110177947A; WO2018134598A2; KR20190105594A; JP2020505550A; WO2018134598A3; GB201700998D0; US20190368354A1

Abstract

A multi-stage vacuum pump having an interstage coupling unit vacuum pump is disclosed. The inter-stage coupling for a multi-stage vacuum pump comprises: a first inter-stage coupling part defining a first portion of a void for receiving a common rotor shared by adjacent stages of the multi-stage vacuum pump; and a second inter-stage coupling part separable from the first inter-stage coupling part, the second inter-stage coupling part defining a second portion of the void for receiving the common rotor shared by adjacent stages of the multi-stage vacuum pump. In this way, a coupling is provided which enables an assembled rotor and assembled stages of the vacuum pump to be fixed together, since the assembled rotor can be received within the separable parts of the coupling which, in turn, can be fitted to the assembled adjacent stages. This enables the mechanical integrity of the rotor and adjacent stages to be preserved while still facilitating assembly of the multi-stage vacuum pump.

Description

MULTI-STAGE VACUUM BOOSTER PUMP COUPLING

FIELD OF THE INVENTION

The present invention relates to an inter-stage coupling for a multi-stage vacuum booster pump, a vacuum pump and a method.

BACKGROUND

Vacuum pumps are known. These pumps are typically employed as a

component of a vacuum system to evacuate devices. Also, these pumps are used to evacuate fabrication equipment used in, for example, the production of semi-conductors. Rather than performing compression from a vacuum to atmosphere in a single stage using a single pump, it is known to provide multistage vacuum pumps where each stage performs a portion of the complete compression range required to transition from a vacuum to atmospheric pressure.

Although such multi-stage vacuum pumps provide advantages, they also have their own shortcomings. Accordingly, it is desired to provide an improved arrangement for multi-stage vacuum pumps. SUMMARY

According to a first aspect, there is provided a multi-stage vacuum pump, comprising: a first pumping stage, comprising a first unitary stator; a second pumping stage, comprising a second unitary stator; and an inter-stage coupling unit for coupling said first pumping stage with said second pumping stage, the coupling unit comprising: a first inter-stage coupling part defining a first portion of a void for receiving a common rotor shared by adjacent stages of the multi-stage vacuum pump; and a second inter-stage coupling part separable from the first inter-stage coupling part, the second inter-stage coupling part defining a second portion of the void for receiving the common rotor shared by adjacent stages of the pump. The first aspect recognises that a problem with existing multi-stage vacuum pumps is that providing a mechanically-robust arrangement is difficult to achieve, which makes the pump complex and difficult to assemble. Accordingly, a coupling unit is provided in the multi-stage vacuum pump. The coupling unit may be used to couple different pumping stages of the multi-stage vacuum pump. The coupling may have a first inter-stage coupling part. That first inter-stage coupling part may define or provide a first portion or part of a void or opening which may receive a rotor. That rotor may be shared by or extend into adjacent or neighbouring stages of the vacuum pump. The coupling may also provide a second coupling part. The second coupling part may be separable or

disconnectable from the first coupling part. The second coupling part may define or provide a second portion or part of the void or opening which receives the rotor. In this way, a coupling is provided which enables an assembled rotor and assembled stages of the vacuum pump to be fixed together, since the assembled rotor can be received within the separable parts of the coupling which, in turn, can be fitted to the assembled adjacent stages. This enables the mechanical integrity of the rotor and adjacent stages to be preserved while still facilitating assembly of the multi-stage vacuum pump. In one embodiment, the first inter-stage coupling part and the second inter-stage coupling part are arrangeable in a coupled configuration where the common rotor is retainable by the void and a separated configuration where the common rotor is removable. Accordingly, the two coupling parts can be coupled or fixed together as well as de-coupled or separated to enable the rotor to be retained or removed.

In one embodiment, the void is cylindrical and each of the first portion and the second portion define hemi-cylinders. Accordingly, the coupling part may provide a generally-cylindrical void to receive a corresponding generally-cylindrical rotor.

In one embodiment, the first inter-stage coupling part defines respective first portions of plurality of the voids, each for receiving a respective common rotor shared by adjacent stages of the multi-stage vacuum pump and the second interstage coupling part defines respective second portions of the plurality of voids. Accordingly, more than one void may be provided by the coupling, with each coupling part defining a part of each of those voids. This enables more than one rotor to be received by the coupling part.

In one embodiment, the first inter-stage coupling part defines a first portion of first and second coupling faces and the second inter-stage coupling part defines a second portion of first and second coupling faces and each void extends between the first and second coupling faces. Accordingly, the coupling may present coupling faces and the voids may extend between those faces, through the coupling.

In one embodiment, each of the first and second coupling faces is configured to be received by a respective adjacent stage of the multi-stage vacuum pump. Accordingly, the coupling faces may be dimensioned to attach to or couple with an adjacent stage of the vacuum pump to form one end of a housing of that adjacent stage. In one embodiment, each of the first and second coupling faces is configured as a head plate to seal an end of the respective adjacent stage of the multi-stage vacuum pump. Accordingly, each face may act as a head plate of an adjacent stage to generally seal a periphery of that stage. In one embodiment, the first coupling face defines an inlet aperture to receive an exhaust from a first adjacent stage of the multi-stage vacuum pump and the second coupling face defines an outlet aperture to deliver the exhaust to a second adjacent stage of the multi-stage vacuum pump and the first and second inter-stage coupling parts define a transfer conduit configured to fluidly couple the inlet aperture with the outlet aperture. Accordingly, one coupling face may provide an inlet aperture and the other coupling face may define an outlet aperture. A conduit may extend between the inlet aperture and the outlet aperture. The inlet aperture may receive the exhaust from an adjacent stage. The exhaust may be conveyed by the conduit to the outlet aperture to deliver that exhaust to an inlet of an adjacent stage. Accordingly, the coupling itself may facilitate the transfer of compressed gas from one stage to another, without the need for additional pipework.

In one embodiment, the inlet aperture is located fluidly downstream of the first adjacent stage of the multi-stage vacuum pump and the outlet aperture is located fluidly upstream of the second adjacent stage of the multi-stage vacuum pump. Accordingly, the inlet aperture may receive compressed gas or exhaust from the first stage and deliver that to an inlet of the second stage for further compression.

In one embodiment, one of the first and second portions of the first coupling face defines the inlet aperture and another of the first and second portions of the second coupling face defines the outlet aperture. Accordingly, one of the portions of the coupling may provide the inlet, while the other portion of the coupling may provide the outlet. This enables the exhaust from one stage to be transferred to the inlet of another stage due to the common rotation of the common rotor.

In one embodiment, one of the first and second portions of the first coupling face defines the inlet aperture and another of the first and second portions of the first coupling face defines a recirculation outlet aperture and the first and second inter-stage coupling parts define a recirculation conduit configured to selectively fluidly couple the inlet aperture with the recirculation outlet aperture. Accordingly, one portion of one face may have the inlet aperture and the other portion of that face may have a recirculation aperture. The inlet aperture and the recirculation aperture may be coupled by a recirculation conduit which selectively couples the inlet aperture with the circulation outlet aperture to allow fluid to recirculate when required. In one embodiment, one of the first and second portions of the second coupling face define the outlet aperture and another of the first and second portions of the second coupling face defines a second recirculation outlet aperture and the first and second inter-stage coupling parts define a second recirculation conduit configured to selectively fluidly couple the outlet aperture with the second recirculation outlet aperture. Accordingly, the other face may also have the outlet aperture in one portion and a secondary circulation aperture in the other portion. The outlet aperture and the secondary circulation aperture may be coupled by a second recirculation conduit. The secondary circulation conduit may selectively couple the outlet aperture with the secondary circulation aperture in order to recirculate fluid when required.

In one embodiment, the recirculation conduit comprises a pressure-actuated valve actuatable to couple the inlet aperture with the recirculation outlet aperture in response to a selected pressure differential between the inlet aperture and the recirculation outlet aperture. Accordingly, the recirculation conduit may recirculate fluid when a predetermined pressure differential exists between the inlet aperture and the recirculation outlet aperture in order to prevent damage to that stage of the vacuum pump.

In one embodiment, the second recirculation conduit comprises a second pressure actuated valve actuatable to couple the outlet aperture with the second recirculation outlet aperture in response to a selected pressure differential between the outlet aperture with the second recirculation outlet. Accordingly, the recirculation conduit may recirculate fluid when a predetermined pressure differential exists between the inlet aperture and the recirculation outlet aperture in order to prevent damage to that stage of the vacuum pump.

According to a third aspect, there is provided a method, comprising: receiving a common rotor shared by adjacent stages of a multi-stage vacuum pump in a first portion of a void defined by a first inter-stage coupling part of an inter-stage coupling and in a second portion of the void defined by a second inter-stage coupling part of the inter-stage coupling separable from the first inter-stage coupling part.

In one embodiment, the method comprises receiving the common rotor in the first portion of the void when the first inter-stage coupling part and the second interstage coupling part are in a separated configuration.

In one embodiment, the method comprises retaining the common rotor in the second portion of the void by arranging the first inter-stage coupling part and the second inter-stage coupling part into a coupled configuration.

In one embodiment, the void is cylindrical and each of the first portion and the second portion define hemi-cylinders. In one embodiment, the method comprises receiving a plurality of common rotors in respective first portions of a plurality of the voids and respective second portions of the plurality of voids.

In one embodiment, the first inter-stage coupling part defines a first portion of first and second coupling faces and the second inter-stage coupling part defines a second portion of first and second coupling faces and each void extends between the first and second coupling faces.

In one embodiment, the method comprises receiving a respective adjacent stage of the multi-stage vacuum pump by each of the first and second coupling faces.

In one embodiment, the method comprises sealing an end of the respective adjacent stage of the multi-stage vacuum pump using each of the first and second coupling faces.

In one embodiment, the method comprises receiving an exhaust from a first adjacent stage of the multi-stage vacuum pump through an inlet aperture in the first coupling face, fluidly coupling the inlet aperture with an outlet aperture using a transfer conduit and delivering the exhaust to a second adjacent stage of the multi-stage vacuum pump through an outlet aperture in the second coupling face. In one embodiment, the method comprises locating the inlet aperture fluidly downstream of the first adjacent stage of the multi-stage vacuum pump and locating the outlet aperture fluidly upstream of the second adjacent stage of the multi-stage vacuum pump. In one embodiment, one of the first and second portions of the first coupling face defines the inlet aperture and another of the first and second portions of the second coupling face defines the outlet aperture.

In one embodiment, one of the first and second portions of the first coupling face defines the inlet aperture and another of the first and second portions of the first coupling face defines a recirculation outlet aperture, the first and second interstage coupling parts define a recirculation conduit and the method comprises selectively fluidly coupling the inlet aperture with the recirculation outlet aperture. In one embodiment, one of the first and second portions of the second coupling face define the outlet aperture, another of the first and second portions of the second coupling face defines a second recirculation outlet aperture, the first and second inter-stage coupling parts define a second recirculation conduit and the method comprises selectively fluidly coupling the outlet aperture with the second recirculation outlet aperture.

In one embodiment, the recirculation conduit comprises a pressure actuated valve and the method comprises coupling the inlet aperture with the recirculation outlet aperture in response to a selected pressure differential between the inlet aperture and the recirculation outlet aperture. In one embodiment, the second recirculation conduit comprises a second pressure actuated valve and the method comprises coupling the outlet aperture with the second recirculation outlet aperture in response to a selected pressure differential between the outlet aperture with the second recirculation outlet.

Further particular and preferred aspects are set out in the accompanying independent and dependent claims. Features of the dependent claims may be combined with features of the independent claims as appropriate, and in combinations other than those explicitly set out in the claims.

Where an apparatus feature is described as being operable to provide a function, it will be appreciated that this includes an apparatus feature which provides that function or which is adapted or configured to provide that function. BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which:

Figures 1 A and 1 B illustrate a two-stage booster pump according to one embodiment;

Figure 2 is a perspective view of a rotor used in the two-stage booster pump of Figures 1A and 1 B;

Figure 3 is a perspective view of a two stage booster pump according to a further embodiment;

Figure 4 is an exploded view of the pump of Figure 3;

Figure 5 illustrates an interstage coupling unit; and

Figure 6 illustrates an alternatively configured coupling unit.

DESCRIPTION OF THE EMBODIMENTS

Before discussing the embodiments in any more detail, first an overview will be provided. Embodiments provide an arrangement which couples or joins adjacent stages of a multi-stage vacuum pump. The coupling assembly, which is located between the two adjacent stages, is a multi-component arrangement. The coupling assembly can be located outside the stator housings of adjacent stages or within one or more stator housings of adjacent stages. The coupling assembly can be separated to enable a unitary or one-piece rotor to be used which extends from one stage into the other. That is to say, rather than the rotor needing to be made from separate components and then assembled in-situ, instead the rotor can be machined as a single item and the coupling assembled around that rotor. This provides for a significantly more robust rotor which is less prone to failure. The coupling assembly can be separated to also enable a generally-unitary housing to be used by each stage. That is to say, rather than the housing of each stage needing to be made from separate components and then assembled, instead the housing can be machined as a single item and the coupling

assembled to complete the housing. This provides for a significantly more robust housing which is less prone to failure. The coupling acts as a head plate between the stages and conveys the exhaust of an upstream stage to the inlet of a downstream stage. This provides for a simplified arrangement which avoids the need for external pipework to convey gases between the stages. Also, the coupling can house a recirculation valve which fluidly couples a stage's outlet with its inlet in the presence of a high pressure differential in order to reduce damage.

Two-stage Pump

Figures 1A and 1 B illustrate a two-stage booster pump, generally 10, according to one embodiment. A first pumping stage 20 is coupled with a second pumping stage 30 via an inter-stage coupling unit 40. The first pumping stage 20 has a first stage inlet 20A and a first stage exhaust 20B. The second pumping stage 30 has a second stage inlet 30A and a second stage exhaust 30B.

Coupling

The inter-stage coupling 40 is formed from a first portion 40A and a second portion 40B. The first portion 40A is releasably fixable to the second portion 40B. When brought together, the first and second portions 40A, 40B define a gallery 130 within the interstage coupling unit 40, through which gas may pass during operation of the vacuum pump. The inter-stage coupling unit 40 defines a cylindrical void 100 which extends through the width of the inter-stage coupling unit 40. The first portion 40A forms a first portion of the void 100 and the second portion 40B forms a second portion of the void 100. The void 100 separates to receive a one piece rotor 50, as will now be described in more detail.

Rotor

Figure 2 is a perspective view of the rotor 50. The rotor 50 is a rotor of the type used in a positive displacement lobe pump which utilises meshing pairs of lobes. Each rotor has a pair of lobes formed symmetrically about a rotatable shaft.

Each lobe 55 is defined by alternating tangential sections of curves. The curves can be of any suitable form such as circular arcs, or hypocycloidal and

epicycloidal curves, or a combination of these, as is known. In this example, the rotor 50 is unitary, machined from a single metal element and cylindrical voids 58 extend axially through the lobes 55 to reduce mass.

A first axial end 60 of the shaft is received within a bearing provided by a head plate (not shown) of the first pumping stage 20 and extends from a first rotary vane portion 90A which is received within a stator of the first stage 20. An intermediate axial portion 80 extends from the first rotary vane portion 90A and is received within the void 100. The void 100 provides a close fit on the surface of the intermediate axial portion 80, but does not act as a bearing. A second rotary vane portion 90B extends axially from the intermediate axial portion 80 and is received within a stator of the second stage 30. A second axial end 70 extends axially from the second rotary vane portion 90B. The second axial end 70 is received by a bearing in a head plate (not shown) of the second pumping stage 30. The rotor 50 is machined as a single part, with cutters forming the surface of the pair of lobes 55. The axial portions 60, 70, 80 are being turned to form the first rotary vane portion 90A and the second rotary vane portion 90B.

As will be understood, a second rotor 50 (not shown) is received within a second void 100 which also extends through the width of the inter-stage coupling 40 but is laterally spaced from the first void 100. The second rotor 50 is identical to the aforementioned rotor 50 and is rotationally offset by 90° thereto so that the two rotors 50 mesh in synchronism. Pump Stage Stators

Returning to Figure 1 A, the first pumping stage 20 comprises a unitary stator 22, forming a chamber 24 therewithin. The chamber 24 being sealed at one end by the head plate (not shown) and at the other end by the inter-stage coupling unit 40. The unitary stator 22 has a first inner surface 20C. In this embodiment, the first inner surface 20C is defined by equal semi-circular portions coupled to straight sections which extend tangentially between the semi-circular portions to define a void/ chamber 24 which receives the rotors 50. However, embodiments may also define a generally-figure-of-eight cross-section void. The second pumping stage 30 comprises a unitary stator 32 forming a chamber 34

therewithin. The chamber 34 being sealed at one end by the head plate (not shown) and at the other end by the inter-stage coupling unit 40. The unitary stator 32 has a second inner surface 30C defining a slightly figure-of-eight cross- sectional chamber 34 which receives the rotors 50. The presence of the unitary stators 22, 32 greatly increases the mechanical integrity and reduces the complexity of the first pumping stage 20 and the second pumping stage 30. In an alternative embodiment, the head plate could also be integrated into each stator unit 22, 32 to form a bucket type arrangement, such an approach would further reduce the number of components present. The first rotary vane portions 90A of the rotors 50 mesh in operation and follow the first inner surface 20C to compress gas provided from an upstream device or apparatus at a first stage inlet 20A and provide the compressed gas at a first stage exhaust 20B. The compressed gas provided at the first stage exhaust 20B passes through an inlet aperture 120A formed in a first face 1 10A of the inter- stage coupling unit 40. The first face 1 10A represents a boundary between the first pumping stage 20 and the gallery 130. The compressed gas travels through the gallery 130 formed within the inter-stage coupling unit 40 and exits through an outlet aperture 120B in a second face 1 10B of the inter-stage coupling unit 40. The second face 1 10B represents a boundary between the gallery 130 and the second pumping stage 30. The compressed gas exiting the outlet aperture 120B is received at a second stage inlet 30A. The compressed gas received at the second stage inlet 30A is further compressed by the second rotary vane portions 90B of the rotors 50 as they mesh and follow the second inner surface 30C and the gas exits via a second stage exhaust 30B.

Assembly

The assembly of the two-stage booster pump 10 is typically performed on a turnover fixture. The unitary stator 22 of the first pumping stage 20 is secured to the build fixture. The head plate is attached to the stator 22 and then the assembly rotated through 180 degrees. The two rotors 50 are lowered into the first stage stator 22. The first portion 40A and the second portion 40B of the inter-stage coupling 40 are slid together over the intermediate axial portion 80 to retain first rotary vane portion 90A within the first pumping stage 20. The first portion 40A and the second portion 40B of the inter-stage coupling unit 40 are then typically dowelled and bolted together. The assembled halves of the inter-stage coupling 40 are then attached to the unitary stator 22 of the first pumping stage 20.

The unitary stator 32 of the second pumping stage 30 is now carefully lowered over the second rotary vane portion 90B and attached to the inter-stage coupling unit 40.

A head plate is now attached to the unitary stator 32 of the second stage pump 30. The two rotors 50 are retained by bearings in the two head plates. Modified Coupling

Figures 3 and 4 illustrate a two-stage booster pump, generally 10', according to one embodiment. A first pumping stage 20' is coupled with a second pumping stage 30' via an inter-stage coupling unit 40'. The inter-stage coupling 40' is located within a housing or stator 32' of the second pumping stage 30'. As such the inter-stage coupling 40' reuses the housing/ stator 32' of the second pumping stage 30' as part of its structure, which provides for a simplified construction by reducing the number of parts and increases reliability by reducing the number of external seals. In Figure 4, the stator 32' of the second stage pump 30' has been moved away to show the two halves of the inter-stage coupling 40'. In this embodiment, as more clearly illustrated in Figure 5, an axially extending curved web or skin 1 12 is provided along at least a portion of an outer periphery of plates 1 10A', 1 10B' to form a box section, defining the gallery 130'.

Returning to Figure 4, the inter-stage coupling 40' is formed from a first portion 40A and a second portion 40B'. As can be seen, a pair of rotors 50 have been inserted into the bore of the first stage pump 20'. Also, the second portion 40B' has been inserted into place. The first portion 40A is releasably fixable to the second portion 40B'. The first portion 40A and second portion 40B' may be secured, if required. This could be done using grub screws inserted radially through the stator wall into the flanges on the inter-stage coupling 40'. These screws could be sealed using a sealant or PTFE tape.

The inter-stage coupling 40' defines cylindrical voids 100' which extend through the width of the inter-stage coupling 40'. The first portion 40A forms a first portion of each void 100' and the second portion 40B' forms a second portion of each void 100'. Each void 100' separates to receive the one piece rotor 50.

The first stage pump 20' is formed from a unitary chamber sealed at one end by a head plate (not shown) and at the other end by a combination of the second stage pump 30' and the inter-stage coupling 40'. The second stage pump 30' is formed from a unitary chamber sealed at one end by a head plate (not shown) and at the other end by a combination of the first stage pump 20' and the interstage coupling 40'. In this embodiment, the inter-stage coupling 40' is located within the second stage pump 30'. The presence of the unitary chambers greatly increases the mechanical integrity and reduces the complexity of the first stage pump 20' and second stage pump 30'. Once again, in an alternative, the head plate may be integrated with the stator of the second stage pump to provide a "bucket" type stator unit.

The first portion 40A' and the second portion 40B' are configured to be located within a bore in the stator 32' of the second stage pump 30'. The bore is slightly larger than the bores in which the rotors 50 rotate. This axial ly-locates the interstage coupling 40' between this small step in the second stage bore and the stator 22' of the first stage pump 20' whose rotor bores are the same as in the second stage stator. The first rotary vane portions 90A of the rotors 50 mesh in operation and follow a first inner surface 20C to compress gas provided from an upstream device or apparatus at a first stage inlet 20A' and provide the compressed gas at a first stage exhaust. The compressed gas provided at the first stage exhaust passes through an inlet aperture 120A coupled with the inter-stage coupling 40'. The compressed gas travels through a gallery 130' formed within the inter-stage coupling 40' and exits through an outlet aperture 120B' coupled with the interstage coupling 40'. The compressed gas exiting the outlet aperture 120B' is received at a second stage inlet. The compressed gas received at the second stage inlet is further compressed by the second rotary vane portions 90B of the rotors 50 as they mesh and follow an inner surface of the second stage pump 30' and exits via a second stage exhaust 30B'.

In an alternative embodiment as illustrated in Figure 6, axially extending spacer rods 1 14 are provided between plates 1 10A", 1 10B" to form the gallery 130, the outer extent of the gallery being defined by the stator 32 itself. Accordingly, it can be seen that embodiments provide a coupling which couples stages of a multi-stage vacuum pump. That is to say, the coupling sits between stages of a multi-stage vacuum pump. The multi-stage vacuum pump may have any number of stages and one or more couplings may sit between any adjacent two of those stages which need not be the first and second stages of the pump. The coupling has an opposing pair of outwardly-facing coupling faces which attach to adjacent stages. The coupling has an internal arrangement which couples an inlet formed in one coupling face with an outlet formed in that coupling face. The arrangement may have a valve which selectively couples the inlet with the outlet in response to a pressure differential between the two. This coupling recirculates excess gas from an exhaust of the adjacent stage back to the inlet of that stage, in order to reduce strain on that stage of the pump, should a so-called "gas dump" occur where excess gas is introduced into the exhaust of that stage, such as may occur when venting the pump. A variety of different pressure actuated valve arrangements could be implemented, some embodiments may reuse an existing inter-stage transfer conduit to provide a portion of the recirculator.

Accordingly, it can be seen that embodiments provide a two-stage booster having a clamshell coupling unit (transfer stage/transfer port). Both the first and second stage booster rotors run in conventionally-machined one-piece stators. The transfer port to take gas from the first stage to the second stage is of a clamshell design consisting of two halves split along the axis of both rotors.

Embodiments recognise that conventional booster stators are of a one-piece design. These are easy to machine and very strong in the event of a rotor failure. However, embodiments also recognise that with a two-stage booster using three separate stator components (a first stage stator, a one-piece transfer stage and a second stage stator), the second stage booster rotors would have to be separate components in order to assemble the pump.

Embodiments also recognise that if a one-piece rotor was used, then top and bottom clamshell stators could house first and second stage rotors and form the transfer stage. However, these two components would have to be designed to be very stiff to avoid distortion during machining and assembly. They would also be relatively difficult to machine due to their size. Embodiments enable the use of one-piece rotors and easily machined components. Both the first and second stage booster rotors run in

conventionally-machined one-piece stators. The transfer stage takes gas from the first stage exhaust outlet to the second stage inlet and is of a clamshell design consisting of two halves split along the axis of both rotors.

Embodiments maintain the easy manufacture and high strength of one-piece stators, but make use of a clamshell for the transfer stage. This enables assembly of a one-piece rotor design for a two-stage booster. Embodiments provide multistage pumps, particularly those of roots designs. By using a clamshell transfer stage and one-piece through-bore stators, tighter tolerances can be maintained. Through-bored stators enable the use of rotors without a tip radius that is normally required to clear the radius in the corners of blind stator bores. The improved accuracy of components and tighter tolerance control may enable a five stage roots design, rather than a six or seven stage design that would still be capable of the same low pressures.

In one embodiment the clamshell halves of the interstage coupling unit extend to the outside of the pump. In another embodiment the clam shell halves of the interstage coupling are housed in one end of a stator component. In particular, the clam shell halves may be housed within one of the two stators, preferably in the shorter second stage stator.

Although illustrative embodiments of the invention have been disclosed in detail herein, with reference to the accompanying drawings, it is understood that the invention is not limited to the precise embodiment and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope of the invention as defined by the appended claims and their equivalents.

REFERENCE SIGNS two-stage booster pump 10; 10'

first stage pump 20; 20'

first stage inlet 20A; 20A'

first stage exhaust 20B

first inner surface 20C; 20C

second stage pump 30; 30'

second stage inlet 30A

second stage exhaust 30B; 30B'

second inner surface 30C

inter-stage coupling 40; 40C

first portion 40A; 40A

second portion 40B; 40B'

rotor 50, 50'; 50A; 50B first axial end 60

second axial end 70

intermediate axial portion 80; 80A

first rotary vane portion 90A

second rotary vane portion 90B

void 100; 100'

first face 1 10A

second face 1 10B

inlet aperture 120A; 120A; 120C outlet aperture 120B; 120B'; 120D; 120E gallery 130; 130'

transfer conduit 140; 140'

Claims

A multi-stage vacuum pump, comprising: a first pumping stage, comprising a first unitary stator;

a second pumping stage, comprising a second unitary stator; and an inter-stage coupling unit for coupling said first pumping stage with said second pumping stage, the coupling unit comprising:

a first inter-stage coupling part, defining a first portion of a void for receiving a common rotor shared by adjacent stages of the pump; and a second inter-stage coupling part separable from said first interstage coupling part, said second inter-stage coupling part defining a second portion of said void for receiving said common rotor shared by adjacent stages of the pump.

The vacuum pump according to Claim 1 , wherein the second unitary stator is configured to receive the interstage coupling unit therewithin.

The vacuum pump according to Claim 1 or Claim 2, wherein said first inter-stage coupling part defines a first portion of first and second coupling faces and said second inter-stage coupling part defines a second portion of first and second coupling faces and each void extends between said first and second coupling faces.

The vacuum pump according to Claim 3, wherein each of said first and second coupling faces is configured to be received by a respective adjacent stage of said multi-stage vacuum pump.

5. The vacuum pump according to Claim 3 or Claim 4, wherein each of said first and second coupling faces is configured as a head plate to seal an end of said respective adjacent stage of said multi-stage vacuum pump. The vacuum pump according to any one of Claims 3 to 5, wherein said first coupling face defines an inlet aperture to receive an exhaust from a first adjacent stage of said multi-stage vacuum pump and said second coupling face defines an outlet aperture to deliver said exhaust to a second adjacent stage of said multi-stage vacuum pump and said first and second inter-stage coupling parts define a transfer conduit configured to fluidly couple said inlet aperture with said outlet aperture.

The vacuum pump according to Claim 6, wherein said inlet aperture is located fluidly downstream of said first adjacent stage of said multi-stage vacuum pump and said outlet aperture is located fluidly upstream of said second adjacent stage of said multi-stage vacuum pump.

The vacuum pump according to any one of Claims 3 to 7, wherein one of said first and second portions of said first coupling face defines said inlet aperture and another of said first and second portions of said second coupling face defines said outlet aperture.

The vacuum pump according to any one of Claims 3 to 8, wherein one of said first and second portions of said first coupling face defines said inlet aperture and another of said first and second portions of said first coupling face defines a recirculation outlet aperture and said first and second interstage coupling parts define a recirculation conduit configured to selectively fluidly couple said inlet aperture with said recirculation outlet aperture.

The vacuum pump according to any one of Claims 3 to 9, wherein one of said first and second portions of said second coupling face define said outlet aperture and another of said first and second portions of said second coupling face defines a second recirculation outlet aperture and said first and second inter-stage coupling parts define a second

recirculation conduit configured to selectively fluidly couple said outlet aperture with said second recirculation outlet aperture.

1 1 . The vacuum pump according to Claim 9 or Claim 10, wherein said

recirculation conduit comprises a pressure-actuated valve actuatable to couple said inlet aperture with said recirculation outlet aperture in response to a selected pressure differential between said inlet aperture and said recirculation outlet aperture.

1 2. The vacuum pump according to Claim 1 0 or Claim 1 1 , wherein said

second recirculation conduit comprises a second pressure actuated valve actuatable to couple said outlet aperture with said second recirculation outlet aperture in response to a selected pressure differential between said outlet aperture with said second recirculation outlet.