Vacuum pump and method of sealing a vacuum pump

Abstract

A vacuum pump (200, Fig 2) comprises a stator (210, Fig 2) having first (210a, Fig 2) and second (210b, Fig 2) end faces, and first 212 and second 214 stator components defining a pumping chamber(s) c

Description

FIELD OF THE INVENTION The present invention relates to the field of vacuum pumps. BACKGROUND Vacuum pumps are typically employed as a component of a vacuum system to evacuate working gases from the system. These pumps can be used to evacuate fabrication equipment used in, for example, the production of semiconductors. Whilst compression from a vacuum to atmosphere may be performed in a single stage using a single pump, it is common in such applications to provide multi-stage vacuum pumps wherein each stage performs a portion of the compression range required to transition from a vacuum to atmospheric pressure. Vacuum pumps need to be carefully designed and manufactured in order to ensure the moving parts (i.e., the rotor / s) and the static parts (i.e., the stator) cooperate with each other accurately. Certain components of the vacuum pump are required to be sealed to each other such that a fluid flow can be encouraged through the vacuum pump owing to pressure differences between the pump inlet and the pump outlet. Traditionally, elastomer seals (more specifically T-seals) have been used to seal between the top and bottom stators and end-plates of clamshell roots pumps. An example of a four-piece elastomer T-seal is provided in GB201701268A. SUMMARY OF THE INVENTION In a vacuum pump, the pump mechanism (i.e., the stator and rotor / s) may be kept relatively hot to mitigate the condensation of gases in the pumping chambers of the vacuum pump. The condensation of gases can lead to deposits forming in the vacuum pump which can reduce pump efficiency. Deposition can, in some circumstances, result in clearances between the stator and rotor / s decreasing to an extent that contact occurs between the rotor / s and stator components. It is also desirable that other components of a vacuum pump are kept relatively cool. This includes, for instance, motor components, gears and oil, that may be housed adjacent or within end plates (i.e., head plates) of the vacuum pump. The end plates themselves tend to be arranged in close proximity to i.e., attached to the stator. As vacuum pumps tend to be operated in applications using increasingly harsher chemicals (i.e., for semiconductor fabrication), there becomes an increasing requirement to operate pump mechanisms at higher temperatures whilst balancing the requirement to keep other components of the vacuum pump at lower temperatures. Vacuum pumps also require the pumping chambers to be sealed effectively from ambient. This tends to be achieved in conventional designs through the use of elastomer seals. Particularly, for clamshell pumps, the stator of the vacuum pump comprises first and second stator components (i.e., halfclamshell stator components) that are attached together to define one or more internal pumping chambers. The end faces of the stator components are further attached to the end plates. A four-piece elastomer seal is conventionally used to seal the stator components together, and to seal the end plates to their respective end faces of the stator. The four-piece elastomer seal typically comprises two horizontal gaskets which are received into vertically orientated o-rings (such an arrangement being referred to as a T-seal joint). Owing to the different temperatures of the pump mechanism and the end plates during use of a vacuum pump, a differential expansion of the stator and the end plates tends to be observed. As a result, the inventors have found that the four-piece elastomer seal tends to shear where the horizontal gaskets are received into the vertical o-rings. This tends to result in failure of the seal. To mitigate the failure of the four-piece elastomer seal, a thermal break plate tends to be introduced between the stator and the end plates. The thermal break plates mitigate the heat transfer between the stator and the end plates of the vacuum pump, such that the four-piece elastomer seal seals components of the vacuum pump that are at similar temperatures (and therefore mitigates the shearing effect). Despite the benefits of thermal break plates, the inclusion of such an additional component in a vacuum pump tends to add cost to the vacuum pump, introduces further components requiring servicing and maintenance, increases the volume of the vacuum pump and adds to the tolerance stack of the vacuum pump design. It is an aim of the present disclosure to provide a vacuum pump that mitigates these issues. According to a first aspect, there is provided a vacuum pump, comprising: a stator having a first end face and a second end face, the stator comprising first and second stator components attached together to define at least one pumping chamber; at least one rotor arranged at least partially within the at least one pumping chamber of the stator; first and second end plates respectively attached to the first and second end faces of the stator; and a one-piece sealing gasket arranged to seal the first stator component to the second stator component, the first end plate to the first end face, and the second end plate to the second end face; wherein the vacuum pump further comprises at least one spacer arranged to provide a gap between the first end plate and the first end face and / or between the second end plate and the second end face, wherein the gap extends at least partially across the first end face and / or the second end face. The inventors have found that the use of a one-piece sealing gasket (i.e., a sealing gasket formed as a single continuous piece) tends to be able to tolerate the shearing forces experienced by the differential expansion of the stator and the end plates when the vacuum pump is operated. This tends to be because a one-piece sealing gasket does not have joints, attachments or interfaces that are vulnerable to shearing forces (for instance the T-seal join between horizontal gaskets and vertical o-rings of the prior art). Hence a thermal break plate is not required when using a one-piece sealing gasket to mitigate the shearing forces owing to thermal expansion of vacuum pump components. Accordingly, the stator can be sealed to the end plates using the one-piece seal arrangement. However, a direct contact between the stator and the end plates of the vacuum pump tends to allow for heat transfer between the parts of the vacuum pump that should be kept at different operating temperatures. Accordingly, a gap is maintained between the stator and the end plates through use of the at least one spacer. The gap tends to provide a thermal break without the need for a thermal break plate. Hence the combination of the one-piece sealing gasket and the at least one spacer tend to mitigate the shearing effect observed with prior art systems, enabling removal of thermal break plates from vacuum pumps whilst also maintaining a thermal break feature and effective seal between vacuum pump components. The vacuum pump described herein tends to reduce the cost of vacuum pumps owing not only to the removal of the thermal break plates themselves but also removal of the additional o-rings required for sealing the thermal break plate to the end plates. The vacuum pump described herein tends to reduce the number of vacuum pump components requiring servicing and maintenance. The vacuum pump described herein tends to reduce the volume of the vacuum pump by reducing the length of the vacuum pump through removal of the thermal break plate. This tends to result in the vacuum pump requiring less volume for deployment at customer premises. The vacuum pump described herein tends to have fewer components contributing to a tolerance stack of the vacuum pump, allowing for easier manufacture. The vacuum pump described herein tends to have a reduced leakage owing to the reduced risk of sealing gasket damage from shearing forces resulting from thermal expansion of vacuum pump components. The vacuum pump may be a clamshell dry pump. The end plates may be head plates. The at least one spacer may comprise one, two, three, four, five or greater than five spacers. The number of spacers is not intended to be limiting. Each spacer may have a circular, oval, square or other cross-section. The cross-sectional shape is not however intended to be limiting. The sealing gasket may be a moulded gasket. The sealing gasket may be formed of a deformable material. The sealing gasket may be formed of an elastomer material. The gap may extend substantially across all of the first end face and / or the second end face. The gap may extend across substantially all of the first end face and / or second end face with the exception of where the at least one spacer interfaces with the first end face and / or second end face and where the one-piece sealing gasket interfaces with the first end face and / or second end face. This tends to reduce the direct contact between the end plates and the stator to a minimum, mitigating thermal conduction between the components. The at least one spacer may comprise one or more raised sections, the one or more raised sections being integrally formed with at least one of: the first end face of the stator; the second end face of the stator; the first end plate; and the second end plate. The one or more raised sections may be formed in the end face / s and / or the end plate / s by rebating the end face / s and / or the end plate / s during manufacture. By integrally forming the raised sections with the end face / s and / or the end plate / s the number of parts of the vacuum pump tends not to be increased, mitigating an increase in parts requiring servicing and manufacture and mitigating additional tolerances being added to the overall tolerance stack of the vacuum pump. The at least one spacer may comprise one or more discrete spacers arranged between the first end face and the first end plate and / or between the second end face and the second end plate. By providing discrete spacers, different materials other than the materials of the stator and end plates may be selected for providing the at least one spacer. For instance, relatively highly thermally insulative materials can be chosen. This tends to further improve the thermal break between the stator and end plates. The one or more discrete spacers may be ceramic spacers. Ceramic tends to provide a relatively high thermal insulation between the stator and the end plates. The one or more discrete spacers may be arranged in respective recesses of the first end face, second end face, first end plate and / or second end plate. The recesses tend to retain the discrete spacers during assembly and use of the vacuum pump. The first end plate, the first end face and the at least one spacer may have one or more collocated holes for receiving respective bolts for fastening the first end plate to the first end face via the at least one spacer; and / or the second end plate, the second end face and the at least one spacer may have one or more collocated holes for receiving respective bolts for fastening the second end plate to the second end face via the at least one spacer. The at least one spacer may be located away from the bolts fastening the end plate / s to the stator. However, such arrangements may be challenging to assemble whilst ensuring that the end plate / s and stator do not become misaligned as the end plate / s and stator may pivot or rotate about the spacers when the bolts are fastened. It is preferable therefore for the spacer / s to be collocated with the holes for the bolts and for the bolts to pass through the spacer / s. The gap may be less than or equal to 5mm, preferably less than or equal to 2mm, more preferably less than or equal to 1mm, even more preferably 0.6mm. The inventors have found that such gaps tend to be sufficient to mitigate heat transfer between the stator and end plates. The one-piece sealing gasket may comprise a first annular sealing member, comprising a first annular surface and a second annular surface opposite the first annular surface; a second annular sealing member, comprising a third annular surface and a fourth annular surface opposite the third annular surface; a first longitudinal sealing member comprising a first longitudinal surface and a second longitudinal surface opposite the first longitudinal surface; a second longitudinal sealing member, comprising a third longitudinal surface and a fourth longitudinal surface opposite the third longitudinal surface; wherein the first longitudinal sealing member and the second longitudinal sealing member connect the first annular surface to the third annular surface, such that a first continuous surface is defined by the first longitudinal surface, third longitudinal surface, first annular surface and third annular surface, and such that a second continuous surface is defined by the second longitudinal surface, fourth longitudinal surface, first annular surface and third annular surface; wherein the first continuous surface is arranged to oppose the first stator component, the second continuous surface is arranged to oppose the second stator component, the first annular sealing member is arranged between the first end plate and the first end face of the stator, the second annular sealing member is arranged between the second end plate and the second end face of the stator. The one-piece sealing gasket may have rectangular, circular or oval cross-section. The circular or oval cross-sections may be preferred owing to their improved compression characteristics (i.e., compression loads tend to be more uniform). Furthermore, the sealing gasket may have open-section forms i.e., C-section, E-section, V-section or other open section forms. The first continuous surface may comprise a plurality of first curved surface portions, the first curved surface portions being disposed where the first and second longitudinal sealing members respectively connect to the first annular surface and the third annular surface; and / or the second continuous surface may comprise a plurality of second curved surface portions, the plurality of second curved surface portions being disposed where the first and second longitudinal sealing members respectively connect to the first annular surface and the third annular surface. The first and / or second curved surface portions tend to provide improved and more uniform sealing than abrupt linear changes in angle. In this regard the curved surface portions tend to provide a continuous transition from the annular surfaces to the longitudinal surfaces. Hence compressive loads when the sealing gasket is clamped between stator components of a vacuum pump tend to be applied / distributed in a more unform manner. One or more grooves for receiving the one-piece sealing gasket may be provided in at least one of: the first stator component; the second stator component; the first end plate; and the second end plate. In this respect, the sealing gasket may be considered to be recessed into the grooves. The one or more grooves may be provided in one or both of the stator components and / or end plates, for instance. The one or more grooves may be cut all around the stator and end plate components (i.e., a continuous groove may be formed when the vacuum pump components are attached together). The one or more grooves tend to enable easier alignment and fitting of the sealing gasket to the vacuum pump. The first stator component and / or second stator component may comprise respective first grooves; and the first groove of a respective stator component may extend around an edge of the respective stator component via a transitional groove portion. The transitional groove portion tends to avoid sudden abrupt changes in direction or angle of the one or more grooves. Such sudden abrupt changes in direction or angle can present poor sealing interfaces for the sealing gasket and lead to non-uniform sealing. By providing the transitional groove portion the sealing of the sealing gasket through changes in direction (i.e., at the interfaces of the first grooves) tends to be smooth, continuous and improved. Furthermore, the combination of transitional groove portions and curved portions of the sealing gasket tend to allow the sealing gasket to distort or flow around the edges of the stator without losing firm contact therewith. Hence the arrangement tends to be tolerant of various compression scenarios. The transitional groove portion / s may comprise at least one of: a multifaceted transitional groove portion comprising multiple planar surface portions; a chamfered transitional groove portion comprising a single planar surface portion; a continuous curved surface portion; a curved surface portion and a discontinuity; and a curved surface portion and at least one planar surface portion. According to a second aspect, there is provided a method of sealing a vacuum pump, comprising: providing a stator having a first end face and a second end face, the stator comprising first and second stator components for attaching together to define at least one pumping chamber; providing first and second end plates for attaching respectively to the first and second end faces of the stator; arranging at least one rotor arranged at least partially within the at least one pumping chamber of the stator; arranging a one-piece sealing gasket between the first stator component and the second stator component, between the first end plate and the first end face, and between the second end plate and the second end face; arranging at least one spacer to provide a gap between the first end plate and the first end face and / or between the second end plate and the second end face, wherein the gap extends at least partially across the first end face and / or the second end face; and fastening the first stator component to the second stator component, the first end plate to the first end face, and the second end plate to the second end face. The arranging the at least one spacer may comprise providing one or more raised sections integrally formed with at least one of: the first end face of the stator; the second end face of the stator; the first end plate; and the second end plate. It will be appreciated that particular features of different aspects of the invention tend to share the technical effects and benefits of corresponding features of other aspects of the invention. More specifically, the methods described herein share the same technical benefits as the vacuum pump described herein. It will also be appreciated that the use of the terms “first” and “second”, and the like, are merely intended to help distinguish between similar features and are not intended to indicate a relative importance of one feature over another, unless otherwise specified. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1A shows an example, in isometric view, of a one-piece sealing gasket in accordance with aspects of the present disclosure. Figure 1B shows an example, in side-view, of the one-piece sealing gasket of Figure 1A. Figure 2 shows an example, in cross-section, of a four-piece sealing gasket sealing a stator component to a thermal break plate in a prior art vacuum pump. Figure 3A shows an example, in cross-section, of the one-piece sealing gasket of Figure 1A sealing a stator component to an end plate in a vacuum pump in accordance with aspects of the present disclosure. Figure 3B shows part of the vacuum pump 300 of Figure 3A wherein a first example of a spacer is provided in accordance with aspects of the present disclosure. Figure 3C shows part of the vacuum pump 300 of Figure 3A wherein a further example of a spacer is provided in accordance with aspects of the present disclosure. Figure 3D shows part of the vacuum pump 300 of Figure 3A wherein a further example of a spacer is provided in accordance with aspects of the present disclosure. Figure 4 shows an example, in isometric view, of part of a vacuum pump in accordance with aspects of the present disclosure. Figure 5 shows an example of a method in accordance with aspects of the present disclosure. DETAILED DESCRIPTION Figure 1A shows an example, in isometric view, of a one-piece sealing gasket 100 according to aspects of the present disclosure. The sealing gasket 100 comprises a first annular sealing member 110. The first annular sealing member 110 comprises a first annular surface 112 and a second annular surface 114 opposite the first annular surface 112. The first annular surface 112 may be considered to face inwards. The second annular surface 114 may be considered to face outwards. The sealing gasket 100 further comprises a second annular sealing member 120 spaced apart from the first annular sealing member 110. The second annular sealing member 120 comprises a third annular surface 122 and a fourth annular surface 124 opposite the third annular surface 122. The third annular surface 122 may be considered to face inwards. The third annular surface 124 may be considered to face outwards. The second annular sealing member 120 is arranged such that the third annular surface 122 faces the first annular surface 112. The first annular sealing member 110 and the second annular sealing member 120 are arranged on the same concentric axis such that the third annular surface 122 and the first annular surface 112 are parallel each other and in facing relations. The first annular sealing member 110 and the second annular sealing member 120 may be considered as defining a substantially annular shape in a respective geometrical plane. The first annual sealing member 110 and the second annular sealing member 120 do not comprise sharp edges. The first annular sealing member 110 and the second annular sealing member 120 have a square or rectangular shaped cross section, though a circular cross section or oval cross section may alternatively be used. The annular sealing members 110, 120 may be formed of an elastomer material. The annular sealing members 110, 120 may have a thickness of less than or equal to 20mm, more preferably less than or equal to 10mm, even more preferably less than or equal to 5mm. The sealing gasket 100 further comprises a first longitudinal sealing member 130. The first longitudinal sealing member 130 comprises a first longitudinal surface 132 and a second longitudinal surface 134 opposite the first longitudinal surface 132. The sealing gasket 100 further comprises a second longitudinal sealing member 140 spaced apart from the first longitudinal sealing member 130. The second longitudinal sealing member 140 comprises a third longitudinal surface 142 and a fourth longitudinal surface 144 opposite the third longitudinal surface 142. The longitudinal sealing members 130, 140 are elongate and arranged parallel but spaced apart from each other. The first and third longitudinal surfaces 132, 142 may be considered to face upwards. The second and fourth longitudinal surfaces 134, 144 may be considered to face downwards. The longitudinal sealing members 130, 140 may be formed from an elastomer material. The longitudinal sealing members 130, 140 have a square or rectangular cross section, though a circular or oval cross section may be used. The longitudinal sealing members 130, 140 may have a thickness of less than or equal to 20mm, more preferably less than or equal to 10mm, even more preferably less than or equal to 5mm. The first and second longitudinal sealing members 130, 140 are each connected between the first annular surface 112 of the first annular sealing member 110 and the third annular surface 122 of the second annular sealing member 120. A first continuous surface is defined by the first longitudinal surface 132, third longitudinal surface 142, first annular surface 112 and third annular surface 122. A second continuous surface is defined by the second longitudinal surface 134, fourth longitudinal surface 144, first annular surface 112 and third annular surface 122. The sealing gasket 100 is formed as a single or one piece gasket. In this regard, the annular sealing members 110, 120 and the longitudinal sealing members 130, 140 may be considered as being integrally formed. The sealing gasket 100 may be moulded as a single piece, for instance. The sealing gasket 100 can be used to seal a vacuum pump of the clamshell type. In-use, the sealing gasket 100 is arranged between first and second stator components. More specifically, a first shell stator component is received onto the first continuous surface defined by the surfaces 112, 122, 132, 142. The first shell stator component conforms to the first continuous surface and vice versa. A second shell stator component is received onto the second continuous surface defined by the surfaces 112, 122, 134, 144. The second shell stator component conforms to the second continuous surface and vice versa. A first end plate of the vacuum pump is received against the second annular surface 114. A second end plate of the vacuum pump is received against the fourth annular surface 124. When the shell stator components and end plates are fastened together, the sealing gasket 100 provides a continuous sealing surface between the various components. Figure 1B shows an example, in side-view, of the one-piece sealing gasket 100 of Figure 1A. The second longitudinal sealing member 140 is shown extending from the first annular sealing member 110 and second annular sealing member 120. The second longitudinal sealing member 140 extends from substantially the midpoint of the first annular sealing member 110 and second annular sealing member 120. The second longitudinal sealing member 140 extends substantially orthogonally to the first annular sealing member 110 and second annular sealing member 120. Put differently, the first annular sealing member 110 and second longitudinal sealing member 140 together define a ‘T’ shape. Similarly, the second annular sealing member 120 and the second longitudinal sealing member 140 together define a T shape. This configuration may also be referred to as a ‘T seal’. An equivalent arrangement is provided for the first longitudinal sealing member 130 (not shown in the Figure). The ‘T’ shape is continuous i.e., the one-piece seal 100 does not comprise joins per se where components of the seal 100 merely abut each other. The first continuous surface comprises the first longitudinal surface (not shown), third longitudinal surface 142, a portion 112a of first annular surface and a portion 122a of third annular surface. The second continuous surface comprises the second longitudinal surface (not shown), fourth longitudinal surface 144, another portion 112b of the first annular surface and another portion 122b of the third annular surface. First curved surface portions 150 are disposed where the second longitudinal sealing member 140 respectively connects to the portion 112a of the first annular surface and the portion 122a of the third annular surface. Second curved surface portions 160 are disposed where the second longitudinal sealing member 140 respectively connects to the another portion 112b of the first annular surface and the another portion 122b of the third annular surface. A similar arrangement is apparent from Figure 1A for the connection of the first longitudinal sealing member 130. The provision of the curved surface portions 150, 160 provides a smooth transition between the surfaces 112a, 142 and 122a and between the surfaces 112b, 144 and 122b. Furthermore, the curved surface portions 150, 160 tend to avoid sharp or abrupt changes in direction for the first and second continuous surfaces that may otherwise prove challenging to seal. This achieves a more uniform application of clamping force when the sealing gasket 100 is used to seal between vacuum pump components. Figure 2 shows an example, in cross-section, of a four-piece sealing gasket sealing a stator component to a thermal break plate in a prior art vacuum pump. The vacuum pump 200 is shown as comprising a stator 210. The stator has a first end face 210a and a second end face 210b. The stator 210 is shown as comprising a first stator component 212 and a second stator component 214. The stator components 212, 214 are attached together to define at least one internal pumping chamber (not shown). The at least one pumping chamber may contain one or more rotors (not shown). The attachment may be via bolts (not shown) clamping the stator components 212, 214 together. The vacuum pump 200 further comprises first 222 and second 224 thermal break plates arranged adjacent the end faces 210a, 210b of the stator 210. A four-piece elastomer seal 230 is shown as being between the stator components 212, 214, and thermal break plates 222, 224, to seal the first stator component 212 to the second stator component 214, the first thermal break plate 222 to the first end face 210a, and the second thermal break plate 224 to the second end face 210b. The vacuum pump 200 further comprises first 242 and second 244 end plates (i.e., head plates). The end plates 242, 244 are attached to the thermal break plates 222, 224 via o-rings 252, 254. When the vacuum pump 200 is in-use, the stator 200 operates at a relatively hot temperature, whilst the end plates 242, 244, housing the motor, gears and oil, need to be kept relatively cooler. The difference in temperature tends to cause different amounts of thermal expansion of the stator 200 and end plates 242, 244. The four-piece seal 230 cannot directly seal the stator 200 to the end plates 242, 244 because the different amounts of thermal expansion tends to cause the seal 230 to separate at the joins 230a, 230b. Hence, the thermal break plates 222, 224 are introduced between the stator 210 and the end plates 242, 244. However, the introduction of the thermal break plates 222, 224 adds to the cost of the vacuum pump 200, the servicing and maintenance, and to the tolerance stack of the vacuum pump 200. Figure 3A shows an example, in cross-section, of the one-piece sealing gasket of Figure 1A sealing a stator component to an end plate in a vacuum pump in accordance with aspects of the present disclosure. The vacuum pump 300 is shown as comprising a stator 310. The stator has a first end face 310a and a second end face 310b. The stator 310 is shown as comprising a first stator component 312 and a second stator component 314. The stator components 312, 314 are attached together to define at least one internal pumping chamber (not shown). The at least one pumping chamber may contain one or more rotors (not shown). The attachment may be via bolts (not shown) clamping the stator components 312, 314 together. The vacuum pump 300 further comprises first 342 and second 244 end plates arranged adjacent the end faces 310a, 310b of the stator 310. The one-piece elastomer seal 100 is shown as being between the stator components 312, 314, and end plates plates 342, 344, to seal the first stator component 312 to the second stator component 314, the first end plate 342 to the first end face 310a, and the second end plate 344 to the second end face 310b. The end plates 342, 344 are attached to the stator 310 using bolts (not shown). It is evident that in the vacuum pump 300 there are no thermal break plates. The one-piece seal 100 is able to tolerate the differential thermal expansion of the stator 310 and the end plates 342, 344. However, the conduction of heat from the stator 310 to the end plates 342, 344 still requires mitigation. Accordingly, the vacuum pump 300 comprises at least one spacer 350 arranged to provide a gap 360 between the first end plate 342 and the first end face 310a and / or between the second end plate 344 and the second end face 310b, wherein the gap 360 extends at least partially across the first end face 310a and / or the second end face 310b. The gap 360 shown as being provided by the spacers 350 is 0.6mm and may extend across substantially all of the first end face 310a and second end face 310b. The stator 310 and end plates 342, 344 may be formed from spheroidal Graphite (SG) Iron. The stator 310 may alternatively be formed from stainless steel (SS). SS has a thermal coefficient of expansion which tends to be 70% more than SG and so this material may assist with sealing without a thermal break plate as the stator 310 will thermally expand even more. Examples of the implementation of the at least one spacer 350 will now be described with regard to the spacers 350 arranged between the second end face 310b and the second end plate 344. It will be appreciated that similar arrangements may be provided between the first end face 310a and the first end plate 342. Figure 3B shows part of the vacuum pump 300 of Figure 3A. The part of the vacuum pump 300 shown includes the second end plate 344, stator components 312, 314 and the one-piece seal 100. The at least one spacer 350 comprises two spacers 352, 354 between the stator components 312, 322 and the second end plate 344. The spacers 352, 354 are arranged to provide a gap 360 between the stator components 312, 322 and the second end plate 344. The spacers 352, 354 comprise one or more raised sections integrally formed with the second end face 310b of the stator 320. The spacers 352, 354 may be manufactured by recessing (i.e., machining) away the second end face 310b. Figure 3C shows part of the vacuum pump 300 of Figure 3A. The part of the vacuum pump 300 shown includes the second end plate 344, stator components 312, 314 and the one-piece seal 100. The at least one spacer 350 comprises two spacers 352’, 354’ arranged between the stator components 312, 322 and the second end plate 344. The spacers 352’, 354’ are arranged to provide a gap 360 between the stator components 312, 322 and the second end plate 344. The spacers 352’, 454’ comprise one or more raised sections integrally formed with the second end plate 344. The spacers 352’, 354’ may be manufactured by recessing (i.e., machining) away the second end plate 344. Figure 3D shows part of the vacuum pump 300 of Figure 3A. The part of the vacuum pump 300 shown includes the second end plate 344, stator components 312, 314 and the one-piece seal 100. The at least one spacer 350 comprises two spacers 352”, 354” arranged between the stator components 312, 322 and the second end plate 344. The spacers 352”, 354” are arranged to provide a gap 360 between the stator components 312, 322 and the second end plate 344. The spacers 352”, 454” comprise discrete spacers arranged between the second end face 310b and the second end plate 344. The spacers 352”, 354” are ceramic spacers recessed into the second face 310b and the second end plate 344. In each of the examples of Figure 3A-3D, the gap 360 may extend substantially across the end faces 310a, 310b of the stator 310. This tends to improve the thermal gap achieved between the stator 310 and the end plates 342, 344. Such a gap will now be further described with regard to Figure 4. Figure 4 shows an example, in isometric view, of part of a vacuum pump in accordance with aspects of the present disclosure. The vacuum pump 400 is shown as stator component 414. The stator component 414 has a second end face 414b. The stator components 414 can be seen to have been manufactured to provide part of one or more inner pumping chambers 470. The second end face 414b has been machined to provide a first groove 480 for receiving part of a one-piece sealing gasket 100. The second end face 414b has been machined to provide two raised sections as spacers 454 for providing a gap between the second end face 414b and a second end plate (not shown). The second end face 414b has been machined such that the spacers 454 have one or more collocated holes 454a for receiving respective bolts (not shown) for fastening the second end plate (not shown) to the second end face 414b via the spacers 454. When the second end plate is bolted to the stator component 414 seal 100 will contact the second end plate and become compressed. The seal 100 will be retained by the first groove 480. As the bolts are tightened the second end plate will eventually contact the spacers 454. The second end plate will therefore only contact the second end face 414b directly by the spacers 454 and indirectly via the seal 100. The gap will therefore extend substantially across all of the second end face 414b apart from these regions of contact. Figure 5 shows an example of a method 500 according to aspects of the present disclosure. The method 500 is a method of sealing a vacuum pump. A first step 510 comprises providing a stator having a first end face and a second end face, the stator comprising first and second stator components for attaching together to define at least one pumping chamber. A further step 520 comprises providing first and second end plates for attaching respectively to the first and second end faces of the stator. A further step 530 comprises arranging at least one rotor arranged at least partially within the at least one pumping chamber of the stator. A further step 540 comprises arranging a one-piece sealing gasket between the first stator component and the second stator component, between the first end plate and the first end face, and between the second end plate and the second end face. A further step 550 comprises arranging at least one spacer to provide a gap between the first end plate and the first end face and / or between the second end plate and the second end face, wherein the gap extends at least partially across the first end face and / or the second end face. A further step 560 comprises fastening the first stator component to the second stator component, the first end plate to the first end face, and the second end plate to the second end face. Whilst the examples described herein may indicate a particular number of spacers, the precise number of spacers is not intended to be limiting. Similarly, whilst specific dimensions and / or sizes and / or shapes of spacers may be described herein, other dimensions, sizes and / or shapes of spacers may be used. It should be noted that certain of the process steps depicted in the flowchart of Figure 5 and described above may be omitted or such process steps may be performed in differing order to that presented above and shown in Figure 5. Furthermore, although all the process steps have, for convenience and ease of understanding, been depicted as discrete temporally-sequential steps, nevertheless some of the process steps may in fact be performed simultaneously or at least overlapping to some extent temporally. Although illustrative examples 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 examples 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. Whilst the examples described herein may indicate particular materials for the spacers, other materials may be used. For instance metal spacers, ceramic spacers or thermally insulative materials may be used. Whilst the examples described herein may indicate spacers either integrally formed with end plates, integrally formed with stator components, or discrete spacers, a combination thereof may be used in some examples. Whilst a single-piece elastomer seal may be described herein, other materials for the seal may be used, including metal. Dimensions of the singlepiece elastomer seal are also not intended to be limiting. Whilst the examples described herein refer to the term “annular” it will be appreciated that “substantially annular” configurations are within scope. Whilst the examples described herein may show longitudinal sealing members as being entirely linear, other examples within scope include longitudinal sealing members that comprise laterally deviating sections. It will be appreciated that the particular dimensions of a vacuum pump and vacuum pump components may vary dependent upon application. As may the number of pumping chambers, type of vacuum pump and the number of rotors, for instance. Generally, in addition to the advantages described above, the vacuum pump described herein tends to be operable at increased temperatures, for example in excess of 100°C, 150°C, 200°C. Reference Numeral List 100 one-piece sealing gasket 110 first annular sealing member 112 first annular surface 112a portion of first annular surface 112b another portion of first annular surface 114 second annular surface 120 second annular sealing member 122 third annular surface 122a portion of third annular surface 122b another portion of third annular surface 124 fourth annular surface 130 first longitudinal sealing member 132 first longitudinal surface 134 second longitudinal surface 140 second longitudinal sealing member 142 third longitudinal surface 144 fourth longitudinal surface 150 first curved surface portions 160 second curved surface portions 170 first continuous sealing member 172 first looped section 174 second looped section 176 first longitudinal section 178 second longitudinal section 180 second continuous sealing member 182 third looped section 184 fourth looped section 186 third longitudinal section 188 fourth longitudinal section 189 second curved portions 190 third continuous sealing member 195 fourth continuous sealing member 200 vacuum pump 210 stator 210a first end face 210b second end face 212 first stator component 214 second stator com ponent 222 thermal break plate 224 thermal break plate 230 four-piece seal 230a joint 230b joint 242 first end plate 244 second end plate 252 o-ring 254 o-ring 300 vacuum pump 310 stator 31 Ob second end face 312 first stator component 314 second stator component 342 first end plate 344 second end plate 350 at least one spacer 352 spacer integrally formed with stator 352’ spacer integrally formed with end plate 352” discrete spacer 354 spacer integrally formed with stator 354’ spacer integrally formed with end plate 354” discrete spacer 360 gap 400 part of vacuum pump 414 second stator component 414b second end face 454 spacer 454a bolt hole 470 at least one pumping chamber 480 first groove 500 method 510 step of method 520 step of method 530 step of method 540 step of method 550 step of method 560 step of method

Claims

1. A vacuum pump, comprising:a stator having a first end face and a second end face, the stator comprising first and second stator components attached together to define at 5 least one pumping chamber;at least one rotor arranged at least partially within the at least one pumping chamber of the stator;first and second end plates respectively attached to the first and second end faces of the stator; and10 a one-piece sealing gasket arranged to seal the first stator component tothe second stator component, the first end plate to the first end face, and the second end plate to the second end face;wherein:the vacuum pump further comprises at least one spacer arranged to 15 provide a gap between the first end plate and the first end face and / or between the second end plate and the second end face, wherein the gap extends at least partially across the first end face and / or the second end face;the first end plate, the first end face and the at least one spacer have one or more collocated holes for receiving respective bolts for fastening the first end20 plate to the first end face via the at least one spacer; and / orthe second end plate, the second end face and the at least one spacer have one or more collocated holes for receiving respective bolts for fastening the second end plate to the second end face via the at least one spacer.25 2. The vacuum pump of claim 1, wherein the first end plate and / or secondend plate only contact the first end face and / or the second end face directly by the at least one spacer and indirectly via the one-piece sealing gasket such that the gap extends substantially across all of the first end face and / or the second end face.04 06 253. The vacuum pump of any preceding claim, wherein the at least one spacer comprises one or more raised sections, the one or more raised section being integrally formed with at least one of:5 the first end face of the stator;the second end face of the stator,the first end plate; andthe second end plate.10 4. The vacuum pump of any preceding claim, wherein the at least onespacer comprises one or more discrete spacers arranged between the first end face and the first end plate and / or between the second end face and the second end plate.15 5. The vacuum pump of claim 4, wherein the one or more discrete spacersare ceramic spacers.

6. The vacuum pump of any one of claims 4-5, wherein the one or more discrete spacers are arranged in respective recesses of the first end face, 20 second end face, first end plate and / or second end plate.

7. The vacuum pump of any preceding claim, wherein the gap is less than or equal to 5mm, preferably less than or equal to 2mm, more preferably less than or equal to 1mm, even more preferably 0.6mm.

258. The vacuum pump of any preceding claim, wherein one or more grooves for receiving the one-piece sealing gasket are provided in at least one of:the first stator component;04 06 25the second stator component;the first end plate; andthe second end plate.5 9. A method of sealing a vacuum pump, comprising:providing a stator having a first end face and a second end face, the stator comprising first and second stator components for attaching together to define at least one pumping chamber;providing first and second end plates for attaching respectively to the first 10 and second end faces of the stator;arranging at least one rotor arranged at least partially within the at least one pumping chamber of the stator;arranging a one-piece sealing gasket between the first stator component and the second stator component, between the first end plate and the first end 15 face, and between the second end plate and the second end face;arranging at least one spacer to provide a gap between the first end plate and the first end face and / or between the second end plate and the second end face, wherein the gap extends at least partially across the first end face and / or the second end face; and20 fastening the first stator component to the second stator component, thefirst end plate to the first end face, and the second end plate to the second end face;wherein the first end plate, the first end face and the at least one spacer have one or more collocated holes for receiving respective bolts for fastening 25 the first end plate to the first end face via the at least one spacer; and / orthe second end plate, the second end face and the at least one spacer have one or more collocated holes for receiving respective bolts for fastening the second end plate to the second end face via the at least one spacer.06 2510. The method of claim 9, wherein the arranging at least one spacer comprises providing one or more raised sections integrally formed with at least one of:the first end face of the stator;5 the second end face of the stator,the first end plate; andthe second end plate.

11. The method of claim 9, wherein the arranging the at least one spacer 10 comprises providing one or more discrete spacers arranged between the first end face and the first end plate and / or between the second end face and the second end plate.1533

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