GB2608381A

GB2608381A - Stator assembly for a roots vacuum pump

Info

Publication number: GB2608381A
Application number: GB2109334.9A
Authority: GB
Inventors: Kim Jaeho
Original assignee: Edwards Korea Ltd
Current assignee: Edwards Korea Ltd
Priority date: 2021-06-29
Filing date: 2021-06-29
Publication date: 2023-01-04
Also published as: KR20240000380U; GB202109334D0; WO2023275773A1; TW202323672A

Abstract

A stator assembly for a Roots vacuum pump comprises an inter-stage stator portion 222a-f for separating first and second rotor stages. The inter-stage stator portion comprises a plurality of gas flow passages (G1-3, figure 6) which provide fluid communication between the first and second rotor stages through the inter-stage stator portion. A first passage may extend through a centre of the stator portion, between first and second rotor shaft apertures, with second and third passages extending through first and second side regions of the stator portions which are outside of the first and second rotor shaft apertures. The fluid passages may have a common inlet and outlet. The stator assembly may be formed of two connected stator halves 220a, with the stator portion formed of two connected generally W-shaped portions 140a. The stator assembly may include a plurality of stator portions. A Roots vacuum pump may incorporate the stator assembly, and a method of directing gas through the interstage stator portion is also provided.

Description

STATOR ASSEMBLY FOR A ROOTS VACUUM PUMP

TECHNICAL FIELD

This disclosure relates to a stator assembly for a Roots vacuum pump. This disclosure also relates to a Roots vacuum pump incorporating the assembly, and a method of communicating gas flow through a stator in a Roots vacuum pump.

BACKGROUND

Vacuum systems commonly utilise pumps in order to evacuate gases from the system. One type of vacuum pump used in such systems is a Roots vacuum pump.

A Roots vacuum pump generally includes two counter-rotating shafts with a rotor mounted on each shaft. The rotors include a series of lobes and recesses defined between the lobes. The rotors are mounted such that a lobe of the rotor on one shaft cooperates with a corresponding recess of the rotor on the other shaft.

As the shafts and rotors rotate, gas is trapped and compressed between the cooperating lobes and the recesses. The repeated trapping and compression of gas between the rotors generates a pumping action that can be used to pump gas from an inlet on one side of the rotors to an outlet on the opposite side to evacuate a system.

It is common for Roots vacuum pumps to feature several stages of cooperating rotors; with each stage being axially spaced apart along the shafts and separated by a stator structure. By having multiple stages, progressive increases of gas compression can occur across the pump allowing it to provide a higher degree vacuum for the system in an efficient manner.

It is necessary to communicate the gas between the inlet, rotor stages and outlet. This is commonly achieved by providing a gas flow path between these components that is defined through the stator structure that separates the rotor stages.

Accommodating the gas flow path in the stator structure can negatively increase the length and size of the Roots vacuum pump. Accordingly, there is a need to improve the design of the stator structure and the gas flow path therein to allow for a more compact pump design, without impacting pump efficiency.

SUMMARY -2 -

From one aspect, the present disclosure provides a stator assembly for a Roots vacuum pump in accordance with claim 1.

The plurality of gas flow passages will allow gas that has been compressed by the first rotor stage to be communicated to the next, successive rotor stage for further compression. In order words, the inter-stage stator portion allows communication of gas from the exit of the first rotor stage to the entrance of the second rotor stage.

The first and second rotor stages are generally spaced apart axially along a longitudinal axis, and the inter-stage stator portion is interposed axially between them (i.e., separating them in the axial direction).

The provision of a plurality of gas flow passages through the inter-stage stator portion allows for an increase of flow area through the inter-stage stator without having to increase the size (e.g., thickness or axial length) of the inter-stage stator portion (e.g., compared to known inter-stage stator portion configurations having a single gas flow passage). This can maintain minimal resistance to gas flow through the stator assembly, whilst maintaining a more compact size.

In an embodiment of the above, the inter-stage stator portion includes a first aperture for accommodating a first rotor shaft and a second aperture for accommodating a second rotor shaft.

The first and second apertures allow rotor shafts to pass through the inter-stage stator portion. This means that rotor shafts can rotate to operate the rotor stages without being hindered by the inter-stage stator portion.

The first and second apertures are generally spaced apart in a direction transverse to the longitudinal axis. In some embodiments, the apertures can be sized to give enough clearance around the shafts to allow them to rotate freely therein, or in other embodiments, could include bearings therein that help support the shafts for rotation within the apertures.

In a further embodiment of any of the above, the plurality of gas flow passages comprise a first gas flow passage, a second gas flow passage and a third gas flow passage. The first gas flow passage extends through a central region of the inter-stage stator portion between the first and second apertures. The second gas flow passage extends through a first side region of the inter-stage stator portion around the first aperture. The third gas flow passage extends through a second side region of the inter-stage stator portion around the second aperture. -3 -

The side regions are regions on either side of the central region in a direction transverse to the longitudinal axis. In other words, there is a left side region that is left of the central region transverse to the longitudinal axis (i.e., around the first aperture) and a right side region that is right of the central region transverse to the longitudinal axis (i.e., around the second aperture).

This configuration of gas flow passages provides a balanced flow area around the different regions of the inter-stage stator portion. It also makes better use of all the space available within the inter-stage stator portion to maximise the gas flow area there through. Accordingly, this configuration could allow even more compact inter-stage stator portions to be realised, whilst maintaining pump efficiency.

In a further embodiment of any of the above, the second and third gas flow passages branch off from the first gas flow passage and are fluidly connected thereto at both their start and finish.

In other words, the second and third gas flow passages extend out from the first gas flow passage, extend through the respective side region (i.e., around the respective aperture) and then re-join the first gas flow passage.

This configuration provides a compact arrangement of gas flow passages that communicate the gas flow around the different regions of the inter-stage stator portion.

In a further embodiment of any of the above, the second and third gas flow passages each define a generally C-shaped gas flow path around the respective one of the first and second apertures.

The C-shape of the second and third gas flow passage allow them to curve around the first and second apertures, respectively. This again helps maximise the space available for gas flow through the inter-stage stator portion.

In a further embodiment of any of the above, the stator assembly is formed of two stator halves connected together.

In this way, the stator assembly can be manufactured more simply by casting the two halves separately and then assembling them together. The halves can be fastened together using a removable means (e.g., threaded fasteners). The halves also permit simpler inspection, maintenance and replacement processes for the stator assembly and the rotor components that are housed therein during pump operation. -4 -

In a further embodiment of the above, the inter-stage stator portion is formed by two opposing, generally W-shaped portions that are joined together when the two stator halves are connected together.

In other words, each stator half defines a corresponding half of the inter-stage stator portion, and these half inter-stage stator portions are generally W-shaped in a transverse direction relative to the longitudinal axis.

By generally W-shaped, it is intended that the inter-stage stator portion halves generally form the shape of two conjoined Us across the transverse direction. When the W-shaped inter-stage stator portion halves are joined together they generally form a.3 shape (or two conjoined Os across the transverse direction).

The conjoined region corresponds to the central region of the inter-stage stator portion and the side of each of the 0 shapes that is not conjoined corresponds to the side regions of the inter-stage stator portion. The U/O shapes will generally be defined by recesses in the W-shaped portions that form the first and second apertures when joined together. The recesses can be generally semi-circular in shape and the resulting apertures generally circular in shape.

In yet a further embodiment of the above, the plurality of gas flow passages are formed by a respective plurality of cavities defined through the two generally W-shaped portions that are fluidly connected when the two generally W-shaped portions are joined together.

By having the W-shaped portions forming halves of the inter-stage stator portion, and utilising cavities therein to form the gas flow passages when joined together, a simpler casting mould can be used for stator assembly manufacture (i.e., compared to inter-stage portions that are not split into two halves).

In a further embodiment of any of the above, the inter-stage stator portion comprises an inlet opening for receiving fluid from a first rotor stage and an outlet opening for communicating fluid from the inter-stage stator portion to a second rotor stage. The plurality of gas flow passages are disposed between the inlet and outlet opening and fluidly connect the inlet opening to the outlet opening.

In this manner the plurality of gas flow passages are fed by a common inlet, and delivery gas flow to a common outlet. This can again help simplify the casting mould for manufacture of the stator assembly, and help maintain balanced gas flow distribution through the inter-stage stator portion.

In a further embodiment of any of the above, the stator assembly comprises a plurality of inter-stage stator portions. -5 -

This can allow further the stator assembly to separate further rotor stages. For example, a second inter-stage stator portion can be used to separate the second rotor from a third rotor and communicate gas between the two. Indeed, within the scope of this disclosure, the stator assembly can have any number of inter-stage stator portions according to the number of adjacent rotor stages that need separating whilst enabling fluid communication there between.

From another aspect, the present disclosure provides a (multi-stage) Roots vacuum pump including the stator assembly of the above aspect, or any of its embodiments.

The pump further includes a first (upstream) rotor stage and a second (downstream) rotor stage spaced apart along a longitudinal axis of the pump. The inter-stage stator portion of the stator assembly separating the first rotor stage from the second rotor stage along the longitudinal axis and the plurality of gas flow passages being configured to receive fluid from the first (upstream) rotor stage and communicate the fluid to the second (downstream) rotor stage.

In any embodiment of the above, the pump further comprises a pair of rotor shafts extending along the longitudinal axis, and each rotor stage includes first and second lobed rotors mounted for rotation with a respective one of the rotor shafts.

The respective ones of the rotor shafts will be arranged to pass through the first and second apertures. The apertures may be sized to along the shafts to pass there through and freely rotate therein. In other examples. The aperture could include bearings therein that support the shafts for rotation.

The pump may also include a motor operatively connected to the shafts and configured to drive them to rotate.

By utilising the stator assembly in the Roots vacuum pump the overall length and size of the pump for a given capacity can be reduced. This can open up new applications for the Roots vacuum pump, where a more compact pump is required.

From yet another aspect, the present disclosure provides a method of communicating gas from a first (upstream) rotor stage to a second (downstream), subsequent rotor stage in a (multi-stage) Roots vacuum pump. The method comprises providing a stator assembly having an inter-stage stator portion separating the first and second rotors; and disposing a plurality of gas flow passages through the inter-stage stator portion that are configured to receive fluid from the first rotor stage and communicate the fluid to the second rotor stage. -6 -

The provision of a plurality of gas flow passages through the inter-stage stator portion allows for an increase of flow area through the inter-stage stator without having to increase the size (e.g., thickness or axial length) of the inter-stage stator portion (e.g., compared to known inter-stage stator portion configurations having a single gas flow passage).

In an embodiment of the above, the plurality of gas flow passages comprise a first gas flow passage, a second gas flow passage and a third gas flow passage. The method further includes: defining the first gas flow passage through a central region of the inter-stage stator portion between two apertures for accommodating respective rotor shafts; defining the second gas flow passage through a first side region of the inter-stage stator portion around a first of the two apertures; and defining the third gas flow passage through a second side region of the inter-stage stator portion around a second of the two apertures.

This configuration of gas flow passages provides a balanced flow area around the different regions of the inter-stage stator portion. It also makes better use of all the space available within the inter-stage stator portion to maximise the gas flow area there through.

In any embodiment of either of the above, the plurality of gas flow passages are defined by forming a respective plurality of cavities in two opposing stator halves. The method further comprises: joining the stator halves together such that the respective plurality of cavities are fluidly connected to each other to form respective ones of the plurality of gas flow passages.

This can permit simpler manufacture of the inter-stage stator portions and associated gas flow passages therein, as well as permitting simpler inspection, maintenance and replacement processes thereof.

The method above and its embodiments can utilise the stator assembly and/or Roots vacuum pump discussed in the above aspects, and any of their accompanying embodiments.

Although certain advantages have been discussed in relation to certain features above, other advantages of certain features may become apparent to the

skilled person following the present disclosure.

BRIEF DESCRIPTION OF DRAWINGS

One or more non-limiting embodiments according to the present disclosure will now be described, with reference to the accompanying figures in which: -7 -Figure 1 shows a perspective, top view of an example of a prior art Roots vacuum pump; Figure 2 shows a perspective cross-sectional view of the pump of Figure 1 along line A-A; Figure 3 shows an axial cross-sectional view of the pump of Figure 2 along line B-B; Figure 4A shows a perspective view of the top half of the stator assembly of the pump of Figure 1; Figure 4B shows a perspective view of the bottom half of the stator assembly of the pump of Figure 1; Figure 5A shows a perspective view of the top half of a stator assembly for a Roots vacuum pump in accordance with an embodiment of the present disclosure; Figure 5B shows a perspective view of the bottom half of a stator assembly for a Roots vacuum pump in accordance with an embodiment of the present

disclosure;

Figure 6 shows an axial cross-sectional view of a stator assembly for a Roots vacuum pump in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION

In order to provide a better understanding of the embodiments of the present disclosure, a known multi-stage Roots vacuum pump and a stator assembly thereof are shown in Figures 1 to 4B and discussed below for comparison.

Figure 1 shows a Roots vacuum pump 100 defined along a longitudinal axis L. As is generally known, the pump 100 includes a motor 102 attached to an outer casing 104 at one axial end 104a thereof and an end cap 106 attached to the outer casing 104 at an opposite axial end 104b thereof.

The motor 102 is operatively connected to two rotor shafts including multiple rotor stages mounted thereon. As discussed in the background above, the shafts operate to rotate the rotor stages for pump operation.

The outer casing 104 includes a gas inlet 108 defined at the axial end 104b that is used to communicate gas from the system or environment to be evacuated to the pump 100. The outer casing 104 also features a gas outlet 109 (on the underside of the pump 100) at the opposite axial end 104a that allows the evacuated gas to be exhausted e.g., to the surroundings or atmosphere. -8 -

The gas inlet 108 and gas outlet 109 are apertures passing through the outer casing 104, and can have any suitable shape. They may also include mounting bosses and hardware there around for securing an appropriate inlet and exhaust system (e.g., inlet and exhaust pipework) thereto.

Figure 2 shows a cross-sectional view of the pump 100 along line A-A. The pump 100 includes seven rotor stages 110a-110g spaced axially along the longitudinal axis L (although any number of stages can be used depending on the application). Although seven rotor stages 110a-110g are shown, it is to be understood that the present disclosure is equally suitable for use with a multi-stage Roots vacuum pump 100 having any number of stages, i.e., a plurality of stages/two or more stages.

Although not shown, as is generally known and as discussed above, the rotors stages 110a-110g include cooperating pairs of lobed rotors mounted on respective counter-rotating shafts. The shafts can be supported at either axial end 104a, 104b by bearing assemblies 103a, 103b housed in the motor 102 and end cap 106, respectively.

The outer cover 104 includes a stator assembly 120 that includes inter-stage stator portions 122a-122f that are interposed between each rotor stage 110a-110g. In this manner, the stator portions 122a-122f are used to separate successive rotor stages 110a-110g. The number of inter-stage stator portions 122a-122f will vary according to the number of rotor stages 110a-110g employed in a particular design. The stator portions 122a-122f each define a gas flow passage 124 therein that permits fluid communication between axially adjacent (i.e., successive) rotor stages 110a-110g. In this manner, the stator portions 122a-122f fluidly connect the successive rotor stages 110a-110g in series. The gas flow passages 124 extend generally radially upwards relative to the longitudinal axis, and thus collect compressed gas from the exit of one rotor stage (at the "bottom" of the stator assembly 120) and passes it to the start of the next successive rotor stage (at the "top" of the stator assembly 120).

This results in a gas flow path G through the pump 100 from the gas inlet 108 that passes successively through each rotor stage 110a-110g before being ejected from the gas outlet 109. This gas flow path G ensures that work is done on the gas by each of the rotor stages 110a-110g in a successive fashion, to allow the pump to produce higher levels of compression in any efficient manner. -9 -

Figure 3 is an axial cross-section through the stator portion 122a, where aspects of the construction of the stator assembly 120 can be more clearly seen. The other stator portions 122b-122f also share the same construction and features. Therefore, the description below applies to them also.

The stator assembly 120 is formed of two halves, a top half stator 120a and a bottom half stator 120b. The top and bottom half stators 120a, 120b are secured together by fasteners 130a, 130b, and contact each other along an interface 123.

The fasteners 130a, 130b pass through holes in attachment flanges 132a, 132b defined on each stator half 120a, 120b and are threadably received therein.

This removable attachment means facilitates removal and replacement of the stator halves 120a, 120b for pump assembly, inspection and maintenance activities. Nonetheless, any other suitable attachment means could be employed. For example, welding the stator halves 120a, 120b together along interface 123.

The top and bottom half stators 120a, 120b define gas flow cavities 125a, 125b therein that define the gas flow passage 124 when the half stators 120a, 120b are joined together. The cavities 125a, 125b are hollowed out regions of the half stators 120a, 120b.

The top and bottom half stators 120a, 120b are also complementarily shaped to form two shaft apertures 121. The shaft apertures 121 are formed by defining two generally semi-circular shaft recesses 121a, 121b in the top and bottom half stators 120a, 120b. When the half stators 120a, 120b are joined together, the recesses 121a, 121b accordingly form the two circular shaft apertures 121.

The apertures 121 are positioned and sized to allow the two counter-rotating rotor shafts (not shown) to pass through the stator assembly 120 and rotate the rotor stages 110a-110g for pump operation.

The stator assembly 120 and halves 120a, 120b can be made of any suitable material. For example, a metallic material such as cast iron or graphite iron. Other suitable metallic materials include (but are not limited to) steel alloys and aluminium alloys. As will be appreciated, the particular material can be chosen depending on the particular application and operating conditions thereof.

The stator assembly 120 and halves 120a, 120b can be formed in any suitable manner. For example, they can be cast. In another example, additive manufacturing could be used.

-10 -Although a particular construction of the stator assembly 120 has been discussed above, it should be understood that the stator assembly 120 could be constructed in any other suitable manner.

For example, instead of stator halves 120a, 120b, the stator assembly 120 could instead be formed from a single piece.

The specific shape of the gas flow passage 124 and the apertures 121 (and the recesses 121a, 121b and cavities125a, 125b that form them) can also be readily modified and varied, depending on the needs of a particular application.

Figures 4A and 4B show perspective views of the stator halves 120a and 120b, respectively.

For each successive stator portion 122a-122f, the top stator half 120a includes a respective gas flow cavity 125a defining an opening 126a at the interface 123, and the bottom stator half 120b includes a respective gas flow cavity 125b providing an opening 126b at the interface 123. As will be appreciated, when the stator halves 120a, 120b are joined together, the openings 126a, 126b of each stator portion 122a-122f are joined at the interface 123 and the cavities 125a, 125b thereof are accordingly fluidly connected to form the respective gas flow passages 124.

As depicted, each stator portion 122a-122f is formed by the combination of two generally W-shaped portions 140a, 140b of the top and bottom stator halves 120a, 120b.

By generally W-shaped, it is to be understood that the shape is generally that of two conjoined U shapes. This shape is owing in part to the shaft recesses 121a, 121b being defined in the top and bottom halves of the stator portions 122a- 122f and the gas inlet and gas outlet openings 128, 129 therein (as discussed further below).

However, the stator halves 120a, 120b needn't be limited to just this shape, and any other suitable shape can be possible to accommodate any particular configuration of inlets, outlets and flow passage through the stator portions 122a-122f.

As shown in Figure 3, the cavities 125a, 125b and gas flow passage 124 formed thereby pass radially through the W-shaped portions 140a, 140b in a central region that is defined between the shaft recesses 121a, 121b. Accordingly, the openings 126a, 126b open at the interface at the central region of the W-shaped portions 140a, 140b.

In contrast, the curved U-shaped regions either side of this central region (i.e., around the outside of each shaft recess 121a, 121b) are side regions of the W-shaped portions 140a, 140b (i.e., the left and right hand side regions of the W-shaped portions 140a, 140b). These side regions are solid, and do not include any cavities or openings, unlike the central region.

Each cavity 125b has an inlet opening 128 which guides gas from the exit of a respective rotor stage 110a-110f into the respective gas flow passage 124. Each cavity 125a has an outlet opening 129 through which gas exits the respective gas flow passage 124 to be communicated to the next successive rotor stage 110b-110g.

In the depicted example, the bottom stator half 120b is contoured to provide a scoop 127 underneath each inlet opening 128 to help turn gas flow that exits the rotor stages 110a-110f into the gas flow passage 124. A corresponding scoop (not visible) in the top stator 120a above each outlet opening 129 can also be present to help turn gas flow that exits the gas flow passages 124 into the entrance of the next successive rotor stage 110b-110g.

Both the top and bottom stator halves 120a, 120b include an end plate 131 at the axial end 104a that acts to close off the last rotor stage 110g. This guides the gas flow exiting the last rotor stage 110g to the gas outlet 109 of the pump 100 that is defined through the bottom stator half 120b at the axial end 104a (i.e., axially between final stator portion 122f and end plate 131).

The top and bottom stator halves 120a, 120b both include mounting flanges 133a, 133b at the axial ends 104a, 104b, respectively. The mounting flange 133a at the axial end 104a is for mounting the stator assembly 120 to the motor 102.

The mounting flange 133b at the opposite axial end 104b is for mounting the stator assembly 120 to the end cap 106.

The gas inlet 108 passes through the top stator half 120a axially between the mounting flange 133b and the first stator portion 122a.

The openings 126a, 126b are depicted as substantially rectangular having an axial length and width. However, they can be of any suitable regular or irregular shape (e.g., circular or oval shape) depending on the radial cross-section of the cavities 125a, 125b that form them.

The gas flow passages 124 need to have sufficient flow area to ensure that there is minimal resistance to flow as gas progresses through the rotor stages 110a-110g and stator portions 122a-122f during pump operation. If the flow area -12 -through a particular stator portion 122a-122f is insufficient for the amount of gas being pumped there through, a pressure drop could form that will negatively impact pump efficiency.

As such, the cavities 125a, 125b and openings 126a, 126b are designed to have sufficient volume and flow area to support the pumping of gas there through with minimal flow resistance (i.e., at least up to the maximum intended pumping capacity of the pump 100). The principle way of achieving this is to dimension the cavities 125a, 125b and openings 126a, 126b to provide the gas flow passages 124 with sufficient volume and flow area to accommodate the maximum operational gas flow from each rotor stage 110a-110f.

As the gas passes from the high vacuum side of the pump 100 at the gas inlet 108 to the low vacuum side of the pump 100 at the gas outlet 109 and is successively compressed by the rotor stages 110a-110f, its volume is reduced. As depicted, the size and volume of the gas flow passages 124 will also get progressively smaller to compensate.

The dimensioning of the gas flow passages 124 to have sufficient gas flow capacity after each rotor stage 110a-110f affects the size of the stator portions 122a-122f and corresponding W-shaped portions 140a, 140b thereof. In particular, these portions must have sufficient axial length X to accommodate the necessary size of the cavities 125a, 125b and openings 126a, 126b.

Accordingly, the overall length and size of the pump 100 will be limited by the necessary axial length X of each stator portion 122a-122f.

Figures 5A, 5B and 6 depict embodiments of the present disclosure which are designed to overcome this limitation in pump design. In particular, the embodiments of Figures 5A, 5B and 6 include supplementary gas flow passages that allow sufficient gas flow area to be achieved through the stator portions 122a-122f, whilst allowing a reduction in the axial length X of the stator portions 122a-122f.

The main construction and assembly of the pump and stator assembly (and other suitable examples thereof) discussed above with reference to Figures 1 to 4B is equally applicable to the embodiments of Figures 5A, 5B and 6, and so will not be repeated below.

Accordingly, unless specifically stated, it is to be assumed that the features of Figures 1 to 4B apply to the embodiments of Figures 5A, 5B and 6. Indeed, the same reference numerals for features discussed above in relation to Figures 1 to -13 - 4B will be kept the same in Figures 5A, 5B and 6 where these same features apply and need to be referred to for explanation. Different features will be given a new numeral in the form 2)(x, rather than 1xx.

Figures 5A and 5B show perspective views of top and bottom stator halves 220a and 220b, respectively.

As depicted, the stator halves 220a, 220b correspond to the stator halves 120a, 120b discussed above and share their aforementioned features. However, the stator halves 220a, 220b include additional cavities 225a, 225b, 235a, 235b (and corresponding openings 226a, 226b, 236a, 236b) that form further gas flow passages 224, 234 for communicating gas between the rotor stages 110a-110g.

Figure 6 shows an axial cross-section through the stator portion 222a when the halves 220a, 220b are joined together. Although stator portion 222a is shown, the same features can apply to any of the other stator portions 222b-222f.

Figures 5A and 5B only explicitly shows cavities 225a, 225b, 235a, 235b and openings 226a, 226b, 236a, 236b passing through the first three stator portions 222a, 222b, 222c. This is because in the particular design depicted, the gas is compressed to a small enough volume after the fourth rotor stage 110d that the additional gas flow passages 224, 234 are no longer necessary in further stator portions 222d, 222e, 222 to maintain gas flow without prohibitive flow resistance.

However, it should be understood that the additional gas flow passages 224, 234 can be used in any number of stator portions 222, depending on the gas flow and compression characteristics of a particular design.

As depicted in Figure 6, the cavities 125a, 125b extending through the central regions of the W-shaped portions 140a, 140b provides a first gas flow passage 124 that passes through the centre of the stator portions 122a-122f (i.e., between the shaft apertures 121). The cavities 225a, 225b and 235a 235b (with corresponding openings 226a, 226b and 236a, 236b) extend through the aforementioned side regions of the W-shaped portions 140a, 140b to provide additional second and third gas flow passages 224, 234 that pass through opposed sides of the stator portions 122a-122f (i.e., around the outside of the shaft apertures 121).

In this manner, the side region cavities 225a, 225b and 235a 235b can be seen to provide two opposing generally C-shaped gas flow passages 224 and 234 that pass circumferentially around the outside of a respective shaft aperture 121.

-14 -In can be seen that the central gas flow passage 124 thus provides a first gas flow path Gi through the middle of the stator portion 222a and the second and third gas flow passages 224, 234 provide second and third gas flow paths G2, G3 through the sides of the stator portion 222a.

The additional side region gas flow passages 224, 234 work in tandem with the central region gas flow passages 124 to increase the flow area available to gas passing through the stator portions 122a-122f. This additional flow area means that the axial length X of the stator portions 122a-122f can be reduced whilst maintaining minimal resistance to gas flow.

This can reduce the overall size of the pump 100, which can advantageously lead to a more compact design. This may also open up the Roots vacuum pump design to new use cases, where more compact pumps are desirable.

As depicted in Figure 6, the side region gas flow passages 224, 234 are in fluid communication with the inlet opening 128 at one end via the central region gas flow passage 124 and are in fluid communication with the outlet opening 129 at the other end via the central region gas flow passage 124. In this manner, the side region gas flow passages 224, 234 start from the central region gas flow passage 124 downstream of the inlet 128, curve around the apertures 121, and then rejoin/finish at the central region gas flow passage 124 upstream of the outlet 129. In other words, the side region gas flow passages 224, 234 branch off from the central region gas flow passage 124 and are fluidly connected thereto at both their start and finish points.

It should be understood, however, that within the scope of this disclosure, many different configurations of additional gas flow passages 224, 234 can be provided.

For example, the side gas flow passages 224, 234 may not be C-shaped or connected to/branch off from the central gas flow passage 124. Instead, each side gas flow passage 224, 234 might have a dedicated gas inlet and outlet and/or might be substantially straight passages (or other shape) that passes around the sides of the stator portions 122/shaft apertures 121.

In the same vein, the side gas flow passages 224, 234 (and corresponding cavities 225a, 225b, 235a, 235b and openings 226a, 226b and 236a, 236b) can be made to have any suitable cross-sectional shape (e.g., rectangular, square, circular, oval etc.) according to a particular application's design requirements.

-15 -Furthermore, it should be appreciated that although the depicted configuration provides three gas flow passages 124, 224, 234, the axial length X reduction of the stator portions 222 can still be realised by utilising two gas flow passages instead (e.g., utilising only two of passages 124, 224, 234), or more than three gas flow passages. The number and configuration will depend on the gas flow area and pump size requirements for a particular application.

Nonetheless, it should be noted that by utilising gas flow passages 224, 234 passing around opposing sides of the stator portions, the gas flow will be balanced around the (left and right hand) sides of the stator portions 222. This can advantageously provide a balanced directional flow of gas exiting the stator portions 222 for the next rotor stage to receive.

LIST OF REFERENCE NUMERALS

A list of reference numerals used in the accompanying Figures 1 to 4 is provided for ease of reference: Roots vacuum pump 102 motor 103a, 103b bearing assemblies 104 outer casing 104a, 104b axial ends 106 end cap 108 gas inlet 109 gas outlet 110a-110g rotor stages 120 stator assembly 120a, 120b stator halves 121 shaft aperture 121a, 121b shaft recesses 122a-122f inter-stage stator portions 123 interface 124 central gas flow passage 125a, 125b central gas flow cavities 126a, 126b central gas flow openings 127 inlet scoop 128 gas inlet opening -16 - 129 gas outlet opening 130a, 130b fasteners 131 end plate 132a, 132b attachment flanges 133a, 133b mounting flanges 140a, 140b W-shaped portions 220a, 220b stator halves 222a-222f inter-stage stator portions 224 side gas flow passage 225a, 225b side gas flow cavities 226a, 226b side gas flow openings 234 side gas flow passage 235a, 235b side gas flow cavities 236a, 236b side gas flow openings G gas flow path first gas flow path G2 second gas flow path G3 third gas flow path X stator portion axial length L central longitudinal axis A-A cross-sectional view line B-B cross-sectional view line

Claims

-17 -CLAIMS1. A stator assembly for a Roots vacuum pump comprising: an inter-stage stator portion for separating a first rotor stage and a second rotor stage, wherein the inter-stage stator portion comprises a plurality of gas flow passages defined therein that are configured to provide fluid communication between the first rotor stage and the second rotor stage through the inter-stage stator portion.
2. The stator assembly of claim 1, wherein the inter-stage stator portion includes a first aperture for accommodating a first rotor shaft and a second aperture for accommodating a second rotor shaft.
3. The stator assembly of claim 2, wherein the plurality of gas flow passages comprise a first gas flow passage, a second gas flow passage and a third gas flow passage, wherein the first gas flow passage extends through a central region of the inter-stage stator portion between the first and second apertures, the second gas flow passage extends through a first side region of the inter-stage stator portion around the outside of the first aperture, and the third gas flow passage extends through a second side region of the inter-stage stator portion around the outside of the second aperture.
4. The stator assembly of claim 3, wherein the second and third gas flow passages branch off from the first gas flow passage and are fluidly connected thereto at both their start and finish.
5. The stator assembly of claim 3 or 4, wherein the second and third gas flow passages each define a generally C-shaped gas flow path around the respective one of the first and second apertures.
6. The stator assembly of any preceding claim, wherein the stator assembly is formed of two stator halves connected together.
-18 - 7. The stator assembly of claim 6, wherein the inter-stage stator portion is formed by two opposing, generally W-shaped portions that are joined together when the two stator halves are connected together.
8. The stator assembly of claim 7, wherein the plurality of gas flow passages are formed by a respective plurality of cavities defined through the two generally W-shaped portions that are fluidly connected when the two generally W-shaped portions are joined together.
9. The stator assembly of any preceding claim, wherein the inter-stage stator portion comprises an inlet opening for receiving fluid from a first rotor stage and an outlet opening for communicating fluid from the inter-stage stator portion to a second rotor stage, and wherein the plurality of gas flow passages are disposed between the inlet and outlet opening and fluidly connect the inlet opening to the outlet opening.
10. The stator assembly of any preceding claim, wherein the stator assembly comprises a plurality of inter-stage stator portions.
11. A Roots vacuum pump comprising: a first rotor stage and a second rotor stage spaced apart along a longitudinal axis of the pump; the stator assembly of any preceding claim, wherein the inter-stage stator portion separates the first rotor stage from the second rotor stage along the longitudinal axis and the plurality of gas flow passages are configured to receive fluid from the first rotor stage and communicate the fluid to the second rotor stage.
12. The Roots vacuum pump of claim 11, wherein the pump further comprises a pair of rotor shafts extending along the longitudinal axis, and each rotor stage includes first and second lobed rotors mounted for rotation with a respective one of the rotor shafts.
13. A method of communicating gas from a first rotor stage to a second, subsequent rotor stage in a Roots vacuum pump, the method comprising: -19 -providing a stator assembly having an inter-stage stator portion separating the first and second rotor stages; and disposing a plurality of gas flow passages through the inter-stage stator portion that are configured to receive fluid from the first rotor stage and communicate the fluid to the second rotor stage.
14. The method of claim 13, wherein the plurality of gas flow passages comprise a first gas flow passage, a second gas flow passage and a third gas flow passage, and the method includes: defining the first gas flow passage through a central region of the inter-stage stator portion between two apertures for accommodating respective rotor shafts; defining the second gas flow passage through a first side region of the inter-stage stator portion around a first of the two apertures; and defining the third gas flow passage through a second side region of the inter-stage stator portion around a second of the two apertures.
15. The method of claim 13 or 14, wherein the plurality of gas flow passages are defined by forming a respective plurality of cavities in two opposing stator halves, and the method further comprises: joining the stator halves together such that the respective plurality of cavities are fluidly connected to each other to form respective ones of the plurality of gas flow passages.