GB2631498A

GB2631498A - Pump assembly and vacuum pump with reduced seal requirements

Info

Publication number: GB2631498A
Application number: GB2310174.4A
Authority: GB
Inventors: Long Cainan; Henry North Michael; Kailasam Sivabalan; Edward Tomkins Mark
Original assignee: Edwards Ltd
Current assignee: Edwards Ltd
Priority date: 2023-07-03
Filing date: 2023-07-03
Publication date: 2025-01-08
Also published as: GB202310174D0; WO2025008603A1

Abstract

A pump assembly for a vacuum pump comprises a plurality of pump chambers between an inlet side and an outlet side. A first sealing face 241 of a first assembly component 240 is joined to a second sealing face 251 of a second assembly component 250 to provide a seal for substantially sealing the pump chambers from an exterior of the pump assembly. The seal comprises a labyrinth seal 260 which may comprise at least one continuous ridge 261, preferably a hollow ridge, in the first and/or second sealing face and extending around the pump chambers. The ridge may be detachable from both the first and second sealing faces. The labyrinth seal may further comprise at least one continuous groove 262 in the second and/or first sealing face and extending around the pump chambers for mating with the continuous ridge(s), preferably providing an interference fit. A spacer 263 may be arranged between the first and second sealing faces to define a gap between the first and second components. A sacrificial sealing component may be arranged between the first and second sealing faces. The assembly components may each be a stator component, a thermal break plate or a head plate.

Description

PUMP ASSEMBLY AND VACUUM PUMP WITH REDUCED SEAL REQUIREMENTS

FIELD OF THE INVENTION

The field of the invention relates to vacuum pumps, and more specifically to vacuum pumps that can allow for elastomer seals between assembly components to be reduced or removed.

BACKGROUND

to 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. Rather than performing compression from a vacuum to atmosphere 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.

A clamshell pump is an example of a multi-stage vacuum pump. This type of pump typically requires the use of two stator shell halves and two end plates on the two sides of the stator halves to enclose the pumping area.

Traditionally, longitudinal and annular seals are used between the two stator halves and between the stator halves and the two end plates, respectively, to prevent leakages between the pump and the surrounding environment.

A screw pump is a further example of a multi-stage vacuum pump. This type of pump comprises a pump assembly having two cooperative screw rotors contained within a stator having an inlet side and outlet side. The stator interfaces with end plates to effectively seal the plurality of pump chambers defined by the stator and screw rotors, from an exterior of the pump assembly. The stator and end plates are typically clamped together (for instance using bolts) with annular seals therebetween. -2 -

Traditionally, elastomer seals (such as o-rings) are used to seal assembly components of a pump assembly together in a fluid-tight manner. However, it can still be difficult to achieve an effective seal. Moreover, there are applications where the use of elastomer seals is not desirable. For example, they may be susceptible to degradation and loss of sealing at certain operational temperatures and under certain corrosive process gas environments. Further, they may be susceptible to outgassing and have unacceptable gas permeability under certain conditions. It is also the case that, even at low temperature operation, the removal of elastomer seals can yield 1() desirable benefits such as reducing the cost of a vacuum pump apparatus, mitigating the need for frequent service intervals, and increasing the overall lifespan of a vacuum pump.

Compounding these issues is that some vacuum pumps require a thermal break feature between the pump mechanism and peripheral components (such as pump bearings and oil). This is because a pump mechanism may be required to operate at relatively high temperatures (for instance greater than 150 degrees Celsius) in comparison to the bearings, oil and other components, which must be kept at lower temperatures (for instance, less than 80 degrees Celsius). Hence any sealing mechanism between pump assembly components may also need to consider how such a thermal break between the assembly components can be maintained. Traditionally this has been achieved through the provision of low-conductivity thermal break plates arranged between assembly components, sealed to said assembly components with additional elastomer seals therebetween.

Therefore, a pump assembly for a vacuum pump wherein assembly components can be sealed together in such applications whilst avoiding or reducing the need for elastomer seals, is desirable. -3 -

SUMMARY OF THE INVENTION

In an aspect, there is provided a pump assembly for a vacuum pump, comprising: an inlet side and an outlet side and a plurality of pump chambers arranged therebetween; a first assembly component defining a first sealing face; and a second assembly component defining a second sealing face; wherein the first assembly component and the second assembly component are arranged to be joined together at the first and second sealing faces, thereby providing a seal for substantially sealing the plurality of pump chambers from an exterior of the pump assembly; wherein the seal comprises a labyrinth seal.

The removal of an elastomer seal between two assembly components of a pump assembly will result in a pump assembly that naturally leaks. This leakage is typically directed into the pump from the exterior of the pump assembly, because the pump is operating at sub-atmospheric pressures. It has been found that by providing an interface between assembly components that is tortuous i.e. comprises twists or turns and is generally complex, vice linear or planar, results in an increased path length for gases leaking into the pump assembly and reduces the leakage experienced. Such a labyrinth seal may also comprise limited contact-sealing between the first and second sealing faces, and can encourage controlled fluid vortices between the sealing faces, further providing a sealing effect. Hence the pump assembly can be deployed without elastomer seals and made more suitable for use in higher temperature or more corrosive operating environments where elastomer seals would otherwise be subject to degradation or be unsuitable. This also reduces the costs associated with manufacturing and servicing vacuum pumps comprising the pump assembly, and further mitigates the frequency of servicing that pumps require once deployed. These particular advantages are particularly relevant to screw pumps, multistage roots pumps or roots-claw pumps, and the removal of elastomer seals currently used between stator components, head plates, and thermal break plates.

In some embodiments the labyrinth seal comprises at least one continuous ridge provided in the first sealing face and/or the second sealing -4 -face, the at least one continuous ridge extending around the plurality of pump chambers.

The at least one continuous ridge may be defined by a raised section (having, for instance, a tooth-like cross-section) arranged on the first or second sealing face and extending around the plurality of pump chambers. The at least one continuous ridge may also be defined by an engraving, for instance, that naturally defines a relatively raised section adjacent the engraving. The at least one continuous ridge contributes to the tortuous profile of the labyrinth seal in a direction from the exterior of the pump assembly towards the interior of the pump assembly (i.e. towards the pump chambers). This assists in reducing leakage into the pump assembly, allowing for elastomer seals to be removed. In addition, the at least one continuous ridge assists in reducing the surface area of first and second sealing faces that are immediately adjacent and/or in contact with each other. This helps to reduce heat transfer across the interface, which is particularly relevant where the first and second assembly components are parts of respective sections of the pump assembly that must be maintained at different operational temperatures (for instance, in a screw pump as hereinbefore discussed).

In some embodiments, the at least one continuous ridge comprises at least one hollow ridge.

The at least one continuous ridge may be formed to have a hollow tubelike cross-section or a valley-like cross-section. This can reduce the thermal mass of the at least one continuous ridge, further reducing heat transfer across the labyrinth seal and contributing to a thermal-break type feature.

In some embodiments, the at least one continuous ridge is detachable from both the first and second sealing faces. In this respect, the at least one continuous ridge may define a belt-like structure attachable between the first and second sealing faces (for instance through the location of the belt-like structure in an engraving present in the first and/or second sealing faces). Such embodiments may allow for easier assembly, particularly where the continuous ridge is manufactured to be bendable to accommodate the machining tolerance between the first and second sealing faces. Furthermore, the detachable ridge -5 -could be replaced if required at lower cost than replacing the entire interface (in non-detachable variants) should such a need arise.

In some embodiments, the at least one continuous ridge comprises a plurality of continuous ridges.

By providing a plurality of ridges, the labyrinth seal can be made more tortuous, further mitigating the leakage into the pump assembly, and further enabling the removal of elastomer seals. A plurality of ridges also provides for a more robust and sturdier interface between the first and second sealing faces, whilst still maintaining a reduced surface area of the first and second sealing faces that are in contact (relative to planar sealing surfaces) with each other.

Hence, heat transfer across the labyrinth seal can be reduced whilst still providing a robust interface.

In some embodiments, the labyrinth seal further comprises at least one continuous groove provided in the second sealing face and/or the first sealing 15 face, the at least one continuous groove extending around the plurality of pump chambers, for mating with the at least one continuous ridge.

It has been found that by providing at least one continuous ridge that mates with at least one continuous groove, the interface between the first and second sealing faces can be made robust and strong. Furthermore, the labyrinth seal is made more tortuous, defining further twists and turns encouraging further fluid vortices that all contribute to an improved seal. For a vacuum pump, this further reduces the need for elastomer seals.

In some embodiments the at least one continuous groove provides an interference fit to the at least one continuous ridge.

By providing an interference fit, a contact-seal can be established between the at least one continuous groove and the at least one continuous ridge. This further increases the strength of the interface between the first and second sealing faces, whilst also minimising gas leakage.

Some embodiments further comprise a spacer arranged between the first and second sealing faces, the spacer defining a gap between the first and second components. -6 -

It has been found that providing a spacer encourages a gap to be maintained between the first and second sealing faces that define the labyrinth seal. The gap contributes to a thermal-break feature of the labyrinth seal that reduces heat transfer across the seal. Hence the pump assembly can be used in applications wherein the first and second components form part of respective sections of the pump assembly that must be maintained at different temperatures. For instance, the pump assembly can be used in a screw pump wherein the pump mechanism (of which one of the first or second assembly components forms part thereof) is required to operate at a higher temperature than peripheral components (of which one of the second or first assembly components forms pad thereof). Indeed, a more specific example is where the first component comprises a stator and the second component comprises a head plate. Moreover, the presence of the gap between the first and second assembly components may reduce or eliminate the need for a separate thermal break plate in the pump assembly, thereby enabling easier manufacture and servicing, and reduced cost of manufacture.

As a further advantage of a spacer, the gap defined between the first and second sealing faces allows for additional pockets to be defined in the labyrinth seal. These pockets can encourage fluid vortices further contributing to a sealing effect.

In some embodiments, the spacer comprises a ceramic material that of itself mitigates conduction of heat across the labyrinth seal via the spacer. This is because ceramic material has a low thermal conductivity. Any suitable ceramic material may be used -for instance Alumina, Zirconia, or Magnesia.

Other materials may be used that yield a thermally insulating effect.

Whilst the spacer may be a discrete and separate component to the first and second assembly components, in other embodiments the spacer comprises a protrusion extending from the first or second sealing face.

A spacer that protrudes from the first or second sealing face allows for a reduction of the number of components to provide the labyrinth seal. This reduces manufacturing complexity and cost and reduces complexity and cost of servicing of a vacuum pump comprising the pump assembly. -7 -

In some embodiments, the first or second assembly component comprising the spacer, further comprises a carving arranged adjacent the protrusion to provide a thermal break.

In embodiments wherein the spacer forms part of the first or second assembly component, the spacer will constitute a part of the first or second assembly component that directly contacts the other of the first or second assembly component. Resultantly, the spacer can provide a route for heat transfer across the labyrinth seal. To mitigate this effect, the first or second assembly component comprising the spacer may have a region carved to therefrom to define an engraving that reduces the thermal mass of the first or second assembly component, adjacent the spacer. This allows for heat transfer cross the labyrinth seal to be mitigated.

In some embodiments, the plurality of pump chambers comprises an inlet pump chamber at the inlet side of the pump assembly, configured to receive process gas from a vacuum system, and at least one downstream pump chamber arranged between the inlet pump chamber and the outlet side of the pump assembly; wherein the labyrinth seal further comprises at least one gas pocket; and wherein the first assembly component and/or the second assembly component comprise at least one gas channel arranged to fluidly connect the at least one gas pocket to at least one of the downstream pump chambers, such that the at least one gas pocket can be pressure equalized with a pump pressure of the downstream pump chambers.

The plurality of pump chambers are chambers where the compressive work of the pump is exerted on the process gas and therefore define a plurality of pump stages. The inlet pump chamber therefore corresponds to that of the inlet stage of the pump assembly. The at least one gas channel can communicate with any downstream pump chamber that is not the inlet pump chamber. Hence, the at least one gas pocket can be maintained at a pressure corresponding to the pressure of the pump stage to which it is fluidly connected.

The at least one gas pocket collects leakage gas that has progressed from an exterior of the pump assembly and into the labyrinth seal. The collected gas is fed into the respective downstream pump chamber and removed from the -8 -pump assembly. This further contributes to the sealing effect of the labyrinth seal whilst maintaining the high vacuum efficiency of the pump assembly at the inlet pump chamber.

In a particular alternative embodiment, the first and second sealing faces are planar. One of the first and second sealing faces comprises at least one gas channel extending from the one of the first and second sealing faces to at least one downstream pump chamber of the plurality of pump chambers. In such embodiments, when the first and second sealing faces are clamped together, the labyrinth seal comprises two planar surfaces in abutment, but with the gas to channels providing a tortuous route for gas attempting to leak across the seal.

This is because leakage gas that has progressed from an exterior of the pump assembly is collected by the gas channels (which are pressure equalized with the respective downstream pump chambers) and removed from the pump assembly. This contributes to the sealing effect of the labyrinth seal whilst maintaining the high vacuum efficiency of the pump assembly at the inlet pump chamber.

Some embodiments further comprise a sacrificial sealing component arranged between the first and second sealing faces. The sacrificial sealing component assists in sealing the labyrinth seal and is sacrificial in the sense that it may require servicing. The sacrificial sealing component allows for the first and second assembly components to be joined together with less clamping force, owing to the sealing effect contributed by the sacrificial sealing component. The sacrificial sealing component may comprise a metal, for instance, that will not degrade when subject to the heat or process gases with which the pump assembly is to be operated.

In some embodiments, the first assembly component and the second assembly component are selected from the list of components consisting of: a stator component; a thermal break plate; and a head plate.

In, for instance, a clamshell pump, elastomer seals are typically found between first and second stator components. It is desirable to remove these elastomer seals to reduce cost and improve the service interval of the pump. -9 -

In, for instance, a screw pump, elastomer seals are typically found between stator components and head plates that enclose the plurality of pump chambers. It is also desirable to remove these elastomer seals to reduce cost and improve the service interval of the pump.

Also in, for instance, a screw pump, elastomer seals can be found between thermal break plates and either of stator or head plate components. It is desirable to remove these elastomer seals to reduce cost and improve the service interval of the pump.

The removal of elastomer seals between the components in the examples described herein is particularly relevant where a vacuum pump is to operate with process gases that might degrade elastomer seals; or where one of more of the assembly components is to operate at temperatures that would also degrade or even melt elastomer seals.

In a further aspect of the invention, there is provided a vacuum pump comprising the pump assembly according to any one of claims 1-13.

In a further aspect of the invention, there is provided a method of sealing a first assembly component to a second assembly component in a pump assembly for a vacuum pump, the method comprising: providing, first and second assembly components of a pump assembly, wherein the pump assembly has an inlet side and an outlet side and a plurality of pump chambers arranged therebetween; joining, a first sealing face of the first assembly component to a second sealing face of the second assembly component, thereby providing a seal for substantially sealing the plurality of pump chambers from an exterior of the pump assembly; wherein the method further comprises the step of: configuring the joining of the first and second sealing faces such that the seal comprises a labyrinth seal.

Owing to the various features of the pump assembly of the present disclosure, elastomer seals can be removed from the pump assembly altogether. This includes longitudinal seals as may be provided between respective stator halves in a clamshell pump, annular seals between stator and head plates in a screw pump type design, and seals provided between thermal break plates and stator or head plates.

In particular, the various features of the pump assembly described herein allow for the removal of elastomer seals between thermal break plates and head plates in a screw pump whilst still maintaining the thermal break function in between the plates as well as performance of the screw pump. In effect, a totally elastomer-seal free screw pump design is provided.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 illustrates an embodiment of a pump assembly for a screw pump; Figure 2A illustrates an embodiment of a labyrinth seal as may be used in the screw pump of Figure 1; Figure 2B further illustrates the labyrinth seal of Figure 2A; Figure 2C further illustrates the labyrinth seal of Figure 2A; Figure 3 illustrates a further embodiment of a labyrinth seal as may be used in the screw pump of Figure 1; Figure 4 illustrates a further embodiment of a labyrinth seal as may be used in the screw pump of Figure 1; Figure 5A illustrates a further embodiment of a pump assembly for a screw pump; Figure 5B illustrates an embodiment of a labyrinth seal as may be used in the screw pump of Figure 5A; Figure 6A illustrates an embodiment of a labyrinth seal providing an interference fit; Figure 6B illustrates an alternative embodiment of a labyrinth seal providing an interference fit; Figure 6C illustrates an alternative embodiment of a labyrinth seal providing an interference fit; Figure 7 illustrates an embodiment of a labyrinth seal comprising a hollow ridge; Figure 8A illustrates an embodiment of pump assembly as may be used in a clamshell/roots design pump; Figure 8B further illustrates the embodiment of Figure 8A; Figure 9A illustrates an embodiment of an interface of first and second stator components in a clamshell design pump; Figure 9B illustrates an embodiment of a labyrinth seal as may be used in the embodiment of Figure 9A; and Figure 10 illustrates an embodiment of a method of sealing a first assembly component to a second assembly component in a pump assembly for a vacuum pump.

DETAILED DESCRIPTION

Figure 1 illustrates an embodiment of a pump assembly 100 for a vacuum pump of the screw pump type.

The pump assembly 100 comprises an inlet side 110 and an outlet side 120 and a plurality of pump chambers 130 arranged therebetween. The plurality of pump chambers 130 comprise seven pump chambers 131-137. The first pump chamber 131, also known as the inlet pump chamber 131, is arranged adjacent the inlet side 110. The remaining pump chamber 132-137, also known as downstream pump chambers 132-137, are arranged between the inlet pump chamber 131 towards the outlet side 120. The pump chambers 131-137 decrease in volume from the inlet side 110 to the outlet side 120.

The pump chambers 130 are defined within an enclosure between a first assembly component 140, constituting a stator of the pump assembly, and second assembly components 150, constituting head plates of the pump assembly. The stator 140 comprises a first sealing face 141, and the head plates 150 comprise second sealing faces 151. The first and second sealing faces 141, 151 are arranged to be joined together to provide a seal (highlighted by the circled region 160) for substantially sealing the plurality of pump chambers 130 from an exterior 170 of the pump assembly 100. The seal 160 in the embodiment illustrated will be formed at the outer radial edge of the stator 140 and head plates 150. The seal 160 comprises a labyrinth seal, as will be later described.

The pump chambers 130 themselves are defined between the stator 140, head plates 150 and a rotor 195 illustrated as extending through the enclosure defined between the stator 140 and head plates 150, along a pump axis 'A'. The rotor 195 comprises a rotor shaft 195a and a plurality of rotor blades 195b, defining the respective pump chambers 131-137, that extend outwards from the pump axis 'A'. The rotor 195 may generally include two screw rotors that interact with the chambers 131-137 to progress process gas through the pump assembly from the inlet side 110 to the outlet side 120 (that is, from the higher vacuum side to the lower vacuum side, of the pump assembly 100). Hence as illustrated, the plurality of pump chambers 130 are the chambers wherein compressive work of the pump assembly 100 is exerted on process gas.

The stator 140 is illustrated as comprising at least one gas channel 181, 182, 183, arranged to fluidly connect at least one gas pocket (not visible) of the seal 160 to at least one of the downstream pump chambers 132-137, such that the at least one gas pocket can be pressure equalized with a pump pressure of the downstream pump chambers 132-137. More specifically, two gas channels 181 and 182 are illustrated connecting respectively to pump chambers 133 and 135. The two gas channels 181 and 182 are drilled through the stator 140 longitudinally (along the axis 'A') from the inlet side 110 (high vacuum side) a distance corresponding to the distance from the inlet side 110 to the chambers 133 and 135, respectively. The gas channels 181 and 182 as illustrated are then drilled through the stator 140 perpendicularly to the axis 'A' to connect to the chambers 133 and 135 (although the gas channels 181, 182 could alternatively be drilled through the stator 140 to connected to any of chambers 131-137). A further gas channel 183 is also illustrated as having been drilled through the stator 140 at the outlet side 120 (low vacuum side) to connect to chamber 137.

Also illustrated are thermal break plates 190 that maintain a thermal break between the stator 140 and the head plates 150. The thermal break plates 190 are bolted to the stator 140. In the pump assembly 100 illustrated, the thermal break between the stator 140 and head plates 150 is important, because the stator 140 is configured to operate at a first temperature (for instance, 200 degree Celsius) that is higher than a second temperature (for instance less than 100 degrees Celsius) at which the head plates 150 are configured to operate. It will be appreciated that head plates 150 may comprise, or be in thermal contact with, components of the pump assembly 100 whose operation is temperature sensitive. For instance, the head plates 150 may contain bearings, seals, or oil that support the rotor 195 during operation.

Figure 2A illustrates an embodiment of a labyrinth seal 260 as may be used as the seal 160 in the pump assembly 100 of Figure 1. The illustration is provided in cross-sectional view.

The labyrinth seal 260 is provided between a first sealing face 241 of a stator 240 and a second sealing face 251 of a head plate 250.

The labyrinth seal 260 comprises three continuous ridges 261a, 261b, 261c, provided in the first sealing face 241 of stator 240. As illustrated, the ridges 261 a-261c have a tooth-like cross-section.

The labyrinth seal 260 further comprises three continuous grooves 262a, 262b, 262c, provided in the second sealing face 251 of head plate 250 for mating with the ridges 261a, 261b, 261c.

Furthermore, a spacer 263 is arranged between the first and second sealing faces 241, 251. The spacer 263 defines a gap 265 between stator 240 and head plate 250. The gap 265 may be 0.6mm.

Also illustrated, are gas channels 281 and 282 arranged to fluidly connect gas pockets 264a, 264b, to at least one downstream pump chamber of a pump assembly (for instance, to pump chambers 133 and 135 of Figure 1).

As illustrated, the temperature of operation of the stator 240 is illustrated as '200C' indicating 200 degrees Celsius. The temperature of operation of the head plate 250 is indicated as '80C' indicating 80 degrees Celsius.

Referring now to Figure 2B, which further illustrates the labyrinth seal 260 of Figure 2A, the tortuous profile of the seal 260 is apparent.

Figure 2B illustrates the stator component 240 and head plate 250 clamped together with a bolt. The spacer 263 is therefore squeezed between the first sealing face 241 of stator component 240 and second sealing face 251 of head plate 250. Whilst the spacer 263 is in thermal contact with both the first to and second sealing faced 241 and 251, heat transfer across the spacer 263 is inhibited because the spacer 263 is manufactured from a ceramic material, having low heat conductivity.

As is apparent from Figure 2B, the gap 265 between the first and second contact faces 241 and 251 has been maintained, by virtue of the spacer 263. As is also apparent from Figure 2B, the ridges (261a, for example) mate with (are received into) grooves (262a, for example) in a cooperative manner.

In a direction from an exterior 270 of a pump assembly (for instance 170 of Figure 1) comprising the seal 260, to an interior 230 (for instance 130 of Figure 1), a tortuous path is defined by the seal 260. Gases attempting to leak through the seal 260 must navigate around ridge 261a, through groove 262a, through gas pocket 264b, around ridge 261 b, through groove 262b, through gas pocket 264a, around ridge 261c and through groove 262c. This tortuous path and the fluid vortices it encourages, help to reduce leakage gas propagating through the seal 260.

In addition, an interference fit (highlighted with circle 266) of the ridges 261a-c with grooves 262a-c, further inhibits leakage gas and provides a robust interface between the stator 240 and head plate 250.

In addition, the gas pockets 264a and 264b are pressure equalized with respective pump chambers to which they are connected, by virtue of gas 30 channels 281 and 282. This allows leakage gas to be removed from a pump assembly comprising the labyrinth seal 260. For example, in-use, the gas pocket 264a may be at a pressure of 10m bar and the gas pocket 264b may be at a pressure of 200m bar Referring now to Figure 2C, the interference fit 266 highlighted in Figure 2B will be described in more detail.

As illustrated, using ridge 261a as an example, the ridge 261a is sized to fit snugly into groove 262a of head plate 250. The interference fit is provided on two sides 266a and 266b of the ridge 261 a. This minimises leakage of gas past the ridge 261a whilst also minimising the surface area of ridge 261a in thermal contact with head plate 250.

to Figure 3 illustrates a further embodiment of a labyrinth seal 360 as may be used in the pump assembly 100 of Figure 1. In particular, the labyrinth seal 360 may be used at the outlet side 120 (low vacuum side) of the pump assembly 100.

The figure illustrates a stator component 340 and a head plate 350 having a spacer 363 arranged therebetween. In this embodiment 360, two ridges 361a and 361 b are shown with a tooth-like cross-section protruding from the stator component 340. Cooperative grooves 362a and 362b in the head plate 350 are also shown, for mating with ridges 361a and 361 b. Between the ridges 361a and 361b is a gas pocket 364. The gas pocket 364 is illustrated as being in fluid connection with a gas channel 380. The gas channel 380 is connected to a downstream pump chamber of a pump assembly (for instance, the final pump chamber 137 of Figure 1).

Figure 4 illustrates a further embodiment of a labyrinth seal 460 as may be used in the pump assembly 100 of Figure 1. In this particular embodiment, 25 the seal 460 may be used on the inlet side of a pump assembly.

As illustrated, the labyrinth seal 460 comprises a stator 440 and a head plate 450, with a spacer 463 arranged therebetween. Also illustrated, adjacent (underneath) the spacer 463, is a sacrificial component 467. The seal 460 comprises a plurality of ridges 461 and grooves 462 as have been hereinbefore discussed, in addition to gas pockets 464 and gas channels 480.

The spacer 463, defines a gap 465, as previously discussed with regard to Figures 2A-2C. The sacrificial component 467 is sized to be larger than spacer 463, such that the sacrificial component 467 is compressed between the stator 440 and head plate 450 when the stator 440 and head plate 450 are clamped together. The sacrificial component 467 provides an additional sealing effect during use. Whilst illustrated as a having a circular cross-section, the sacrificial component 467 may have other cross-sectional shapes. The sacrificial component 467 can be formed of a metal.

Advantageously, the presence of a sacrificial component 467 can reduce the clamping force required to clamp the stator 440, head plate 450 and spacer 463 together. This is because sacrificial component 467 contributes to the sealing effect reducing the leakage rate of the seal 460 to a desired level (for instance 10-6m bar 1/s).

Figure 5A illustrates a further embodiment of a pump assembly 500 for a screw pump. The embodiment of the pump assembly 500 is the same as the pump assembly 100 illustrated in Figure 1, with the exception of the labyrinth seal 560 circled in the Figure. In this particular embodiment 500, the stator 540 has been modified to integrate a spacer (not visible) and to comprise a carving 568 providing a thermal break.

Figure 5B further illustrates the labyrinth seal 560 as may be used in the pump assembly 500 of Figure 5A.

As illustrated, the spacer 563 is integrally formed with the stator 540. The spacer 563 therefore resembles a protrusion from the first sealing face 541 of stator 540. The spacer 563 protrudes to define a gap 565 that in-use provides the gap 565 between the first sealing face 541 and a second sealing face 551 of head plate 550.

It will be understood from Figure 5B that, during use, the spacer 563 will abut the second sealing face 551 of head plate 550. Hence the stator 540 and head plate 550 will be in thermal contact. To reduce the potential for heat transfer from the stator 540 to head plate 550, a carving 568 is provided in stator 540. The carving 568 may be continuous around the stator 540. This reduces the thermal conductivity near the interface between the stator 540 and head plate 550.

Whilst the Figures provided and described herein illustrate particular cross-sectional profiles of ridges and grooves, it will be appreciated that a variety of different profiles can be used, that yield a labyrinth seal and provide the benefits of the invention. Further examples will now be briefly described.

Figure 6A illustrates a further embodiment of a labyrinth seal 660 cross-sectional profile. As illustrated, a first assembly component 640 comprises a ridge 661 that provides an interference fit to a groove 662 in a second assembly 10 component 650.

Figure 6B illustrates a further embodiment of a labyrinth seal 660' cross-sectional profile. As illustrated, a first assembly component 640' comprises a ridge 661' that provides an interference fit to a groove 662' in a second assembly component 650'.

Figure 6C illustrates a further embodiment of a labyrinth seal 660" cross-sectional profile. As illustrated, a first assembly component 640" comprises a ridge 661" that provides an interference fit to a groove 662" in a second assembly component 650".

Figure 7 illustrates a further embodiment of a labyrinth seal 760 comprising a hollow ridge 761. Illustrated in cross-sectional view, the hollow ridge 761 resembles a hollow-tooth that has been formed by drilling holes into ridge 761. The hollow ridges 761 of first assembly component 740 assist in reducing thermal conductivity between the ridges 761 and grooves 762 of second assembly component 750. Furthermore, the ridges 761 may bend slightly when inserted into grooves 762, allowing for easier assembly of the seal 760.

Whilst the specific embodiments described herein relate to screw pumps and moreover to the sealing of a stator to a head plate, the full scope of the invention is not so limited. In particular, the invention disclosed herein may be applied to other pump designs and for sealing other assembly components together.

Figure 8A illustrates an embodiment of a pump assembly 800 as may be used in a clamshell design/roots pump.

In a clamshell/roots type pump, the stator 840 comprises a first stator half 841 and a second stator half 842 that are joined together along an interface defined by inner faces 841a and 842a of the stator halves. The joining of the stator halves 841 and 842 define an enclosure that contains a plurality of pump chambers.

A thermal break plate 890 may be arranged between the stator 840 and a head plate 850 as illustrated. The thermal break plate 890 and stator 840 may require sealing to each other, as may the thermal break plate 890 to the head plate 850.

Figure 8B illustrates an embodiment of a labyrinth seal 860 as may be used in the pump assembly 800 of Figure 8A.

The labyrinth seal 860 is formed between thermal break plate 890 and head plate 850. Whilst the labyrinth seal 860 provides the ridges 861, grooves 862 and spacer 863 illustrated, the labyrinth seal 860 may take the form of any of the labyrinth seals 260, 360, 460, 560, 660, 660', 660", 760 as hereinbefore described. Moreover, the gas channels 880 are drilled through the thermal break plate 890.

Figure 9A illustrates an embodiment 900 showing a seal 960 between first 941 and second 942 stator components in a clamshell design pump assembly.

In the embodiment 900, shown in cross-section, the first stator component 941 (upper stator) is arranged atop the second stator component 942 (lower stator) to define an enclosure 995 for a rotor. The first and sector stator components 941, 942, are sealed to each other at their periphery so that seal 960 surrounds the enclosure 995 containing the rotor. Traditionally, the elastomer seals used for this purpose are referred to as longitudinal seals, as they reside in a plane parallel the longitudinal axis of the rotor.

Figure 9B illustrates as an alternative to an elastomer seal, an embodiment of a labyrinth seal 960 as may be used in the embodiment 900 of Figure 9A.

The first 941 and second 942 stator components may be joined together using a labyrinth seal 960 comprising ridges 961 and grooves 962 as hereinbefore discussed with regard to any of the labyrinth seals 260, 360, 460, 560, 660, 660', 660", 760, for instance.

Figure 10 illustrates an embodiment of a method 1000 of sealing a first assembly component to a second assembly component in a pump assembly for 10 a vacuum pump.

A first step 1001 comprises providing, first and second assembly components of a pump assembly, wherein the pump assembly has an inlet side and an outlet side and a plurality of pump chambers arranged therebetween.

A further step 1002 comprises joining, a first sealing face of the first 15 assembly component to a second sealing face of the second assembly component, thereby providing a seal for substantially sealing the plurality of pump chambers from an exterior of the pump assembly.

A further step 1003 comprises configuring the joining of the first and second sealing faces such that the seal comprises a labyrinth seal.

Whilst certain embodiments described herein utilise a spacer (for instance a ceramic spacer), such a spacer can be removed if no thermal break is requirement between a first assembly component and a second assembly component.

Whilst certain embodiments convey a precise number of ridges and 25 grooves forming the labyrinth seal, any number of ridges and grooves may be utilised.

Whilst certain embodiments are not illustrated as comprising a sacrificial component in the labyrinth seal, this is not intended to be limiting. A sacrificial component can be used in any embodiment to reduce the requirement to clamp two assembly components together to a leak-tight level.

-20 -Whilst certain embodiments convey a precise cross-section of a ridge or groove, it will be appreciated that a plurality different ridge and groove shapes and profiles can be used. The ridges and grooves can vary from the cross-sections illustrated and may further extend around the plurality of pump chambers in a continuous manner that is not strictly annular.

Whilst the embodiments illustrated may be described in the particular context of a specific pump type, it will be appreciated that the removal of elastomer seals and replacement with labyrinth seals is applicable across a breadth of vacuum pumps including roots pumps, roots claw pumps, screw pumps and clamshell pumps.

The pump assemblies illustrated may further reside within an additional enclosure filled with a purge gas, such that leakage gas can be controlled.

It will be appreciated that vacuum pumps comprise other components well known in the art, such as motors, bearings and various casings.

is Whilst specific embodiments described herein comprise both ridges and grooves, embodiments of the labyrinth seal may be used that comprise only ridges or grooves. For instance, one of the sealing faces of the assembly components may be planar, and the other sealing face may comprise either ridges or grooves. Alternatively, a detachable ridge may reside between respective grooves in the first and second sealing faces. -21 -

Reference numeral list pump assembly - inlet side outlet side 130 plurality of pump chamber 131 - inlet pump chamber 132-137 - downstream pump chambers - first assembly component 141 - first sealing face to 150 second assembly component 151 - second sealing face - labyrinth seal exterior of pump assembly 181 - gas channel 182 - gas channel 183 gas channel - thermal break plate rotor A' - pump axis 230 - interior of pump assembly 240 - stator 241 first sealing face 250 head plate 251 second sealing face 260 labyrinth seal 261a,b,c - continuous ridges -22 - 262a,b,c - continuous grooves 263 spacer 265 - gap 281 gas channel 282 gas channel 264a,b - gas pockets 266 - interference fit 270 - exterior of pump assembly 340 - stator component 350 head plate 360 - labyrinth seal 361a, b - continuous ridges 362a,b continuous grooves 363 - spacer 364 - gas pocket 380 gas channel 440 - stator 450 head plate 460 - labyrinth seal 461 - plurality of continuous ridges 462 - plurality of continuous grooves 463 spacer 464 gas pocket 465 gap 467 sacrificial component 480 - gas channels 500 - 540 -551 560 - 563 - 568 - 660, 660', 660" 640, 640', 640" 650, 650', 650" 661, 661', 661" 662, 662', 662" 760 - 740 - 761 - 800 - 840 - 841 -841a 842a 850 860 -pump assembly stator first sealing face head plate second sealing face labyrinth seal spacer carving labyrinth seal first assembly component second assembly component ridge groove labyrinth seal first assembly component second assembly component hollow ridge groove pump assembly stator first stator half inner face of first stator half second stator half inner face of second stator half head plate labyrinth seal 861 - ridges 862 grooves 863 - spacer 890 thermal break plate 941 first stator component 942 - second stator component 960 - labyrinth seal 961 - ridges 962 - grooves to 995 enclosure 1000 - method 1001 - providing step 1002 joining step 1003 - configuring step

Claims

-25 -CLAIMSA pump assembly for a vacuum pump, comprising: an inlet side and an outlet side and a plurality of pump chambers arranged therebetween; a first assembly component defining a first sealing face and a second assembly component defining a second sealing face, wherein the first assembly component and the second assembly component are arranged to be joined together at the first and second sealing faces thereby providing a seal for substantially sealing the plurality of pump chambers from an exterior of the pump assembly; wherein the seal comprises a labyrinth seal.
2. A pump assembly according to claim 1, wherein: the labyrinth seal comprises at least one continuous ridge provided in the first sealing face and/or the second sealing face, the at least one continuous ridge extending around the plurality of pump chambers.
3. A pump assembly according to claim 2, wherein: the at least one continuous ridge comprises at least one hollow ridge.
4. A pump assembly according to any one of claims 2-3, wherein: the at least one continuous ridge is detachable from both the first and second sealing faces.
5. A pump assembly according to any one of claims 2-4, wherein: the at least one continuous ridge comprises a plurality of continuous ridges.
A pump assembly according to any one of claims 2-5, wherein: the labyrinth seal further comprises at least one continuous groove provided in the second sealing face and/or the first sealing face, the at least one continuous groove extending around the plurality of pump chambers, for mating with the at least one continuous ridge.
A pump assembly according to claim 6, wherein: the at least one continuous groove provides an interference fit to the at least one continuous ridge.
8. A pump assembly according to any one of claims 6-7, further comprising: a spacer arranged between the first and second sealing faces, the spacer defining a gap between the first and second components.
A pump assembly according to claim 8, wherein: the spacer comprises a protrusion extending from the first or second sealing face.
10. A pump assembly according to claim 9, wherein: the first or second assembly component comprising the spacer, further comprises a carving arranged adjacent the protrusion to provide a thermal break.
11. A pump assembly according to any one of claims 8-10, wherein the plurality of pump chambers comprises an inlet pump chamber at the inlet side of the pump assembly, configured to receive process gas from a vacuum system, and at least one downstream pump chamber arranged between the inlet pump chamber and the outlet side of the pump assembly; wherein the labyrinth seal further comprises at least one gas pocket; and wherein the first assembly component and/or the second assembly component comprise at least one gas channel arranged to fluidly connect the at least one gas pocket to at least one of the downstream pump chambers, such that the at least one gas pocket can be pressure equalized with a pump pressure of the downstream pump chambers.
12. A pump assembly according to any one of claims 8-11, further comprising: a sacrificial sealing component arranged between the first and second sealing faces.
13. A pump assembly according to any preceding claim, wherein: the first assembly component and the second assembly component are selected from the list of components consisting of: a stator component; a thermal break plate; and a head plate.
-28 - 14. A vacuum pump comprising the pump assembly according to any preceding claim.
15. A method of sealing a first assembly component to a second assembly component in a pump assembly for a vacuum pump, the method comprising: providing, first and second assembly components of a pump assembly, wherein the pump assembly has an inlet side and an outlet side and a plurality of pump chambers arranged therebetween; joining, a first sealing face of the first assembly component to a second sealing face of the second assembly component, thereby providing a seal for substantially sealing the plurality of pump chambers from an exterior of the pump assembly; wherein the method further comprises the step of: configuring the joining of the first and second sealing faces such that the seal comprises a labyrinth seal.