GB2590664A

GB2590664A - Sealing between a cover plate and the pumping chamber or a multiple stage pump

Info

Publication number: GB2590664A
Application number: GB1919164.2A
Authority: GB
Inventors: Cekan Vaclav
Original assignee: Edwards sro
Current assignee: Edwards sro
Priority date: 2019-12-23
Filing date: 2019-12-23
Publication date: 2021-07-07
Also published as: WO2021130031A1; GB201919164D0

Abstract

Disclosed is a multi-stage pump which has multiple chambers 18 located in a stator 10 with multiple inter-stage walls 14, where a there is a cover plate mounted to cover a surface of the stator, that surface forming an end surface 20 of the inter-stage walls, where a gasket is mounted between the cover and stator such that it prevents inter-stage leakage and provides a seal between the stator and the cover. The gasket may be rectangular. The gasket may include apertures to allow access for probes. The gasket may include at least one pressure relief aperture between two stages. The pump may be a roots vacuum pump. The pump may include two covers each with a respective gasket. Also claimed is a method of servicing a pump with such a stator, cover and gasket arrangement.

Description

SEALING BETWEEN A COVER PLATE AND THE PUMPING CHAMBER OF A MULTIPLE STAGE PUMP

FIELD OF THE INVENTION

The field of the invention relates to a sealing means for sealing between one or more cover plates and the pumping chamber of a multiple stage pump.

BACKGROUND

Multiple stage pumps such as multiple stage roots-type vacuum pumps are formed with a clam shell stator that contains the stator bore and with two cover plates sealing the top and bottom of the clam shell stator bore.

The upper and lower surfaces of the clam shell stator pieces may conventionally comprise a groove running around an outer edge as is shown in Figure 1. This groove is configured to receive an 0-ring for sealing between the cover plate and the clam shell stator piece. Although this may seal effectively around the edge of the stator and cover plate, the inter-stage walls that extend to the upper and lower surfaces of the clam shell stator pieces seal directly with the cover plate, providing a metal to metal seal and leakage may occur. Sealant may be used to try to address this, but sealant provides its own problems, being complicated to apply and difficult to remove and replace during servicing.

It would be desirable to provide a more effective way of sealing between a portion of a multi-stage stator comprising the stator bore and a cover plate for covering this portion.

SUMMARY

A first aspect provides a multiple stage pump comprising: a stator, said stator comprising at least one portion comprising a stator bore for receiving a rotor, said at least one stator bore portion comprising multiple inter-stage walls for forming multiple pumping stages within said stator; a rotor rotatably mounted within said stator bore; said stator further comprising at least one cover plate covering a -2 -surface of said at least one stator bore portion, said surface comprising end surfaces of said inter-stage walls; and a gasket mounted between said surface of said at least one stator bore portion and said at least one cover plate, said gasket being configured to inhibit leakage between said multiple stages by providing sealing between said inter-stage walls and said at least one cover plate.

The inventor of the present invention recognised that the seal between the inter-stage walls and the cover plate in a multiple stage pump was conventionally a metal to metal seal and leakage problems occurred. Applying glue or some sealant to the surfaces is both expensive and not straightforward to do and makes separating the cover plate and stator at servicing problematic, particularly if the stator material is soft and prone to damage during disassembly. The inventor has addressed these issues by providing a gasket to seal between the cover plate and the stator surface, such that not only is a seal between the pumping chamber and the exterior of the pump provided, but also one between the different stages of the multiple stage pump. This gasket is both simple to manufacture and simple to insert during assembly of the pump and furthermore, makes the separation of the cover plate and stator more straightforward, providing a component that is simple to replace. In this regard, the cover plate and stator become hot during use and may bind together making them difficult to separate, a gasket between the two metal surfaces impedes this from happening as well as providing an effective seal between all of the different surfaces of the stator that contact the cover plate.

Furthermore, for smaller pumps a gasket is easier to handle than other sealing means.

In some embodiments, said gasket comprises a form corresponding to a form of the stator bore portion surface and the cover plate surface. In many embodiments this is a substantially rectangular form. -3 -

In some embodiments, said gasket comprises apertures for receiving components passing between said cover plate and said stator bore portion.

As the gasket provides a sealing barrier between much of the surface of the stator bore and the cover plate, apertures are provided within the gasket to allow components that need to pass between the stator portion and cover plate (such as fixing means for fixing them together) to pass through the gasket.

In some embodiments, said gasket comprises at least one pressure relief aperture configured to provide a passage between said cover plate and at least one of said pumping stages.

Additionally and/or alternatively, the gasket may comprise one or more pressure relief apertures or vents configured to provide a passage between one or more of the pumping stages and the cover plate allowing some venting to occur and impeding the gasket being pulled into the pumping stage where the pump is a vacuum pump.

In some embodiments, said gasket is a substantially solid item, covering at least 20 a majority of a surface of each of said pumping stages.

The gasket is a substantially solid gasket with only a small portion of the surface having one or more apertures for allowing components to pass through and in some case to provide some pressure relief.

In some embodiments, said gasket is between one and two millimetres thick and in some embodiments said gasket is formed of vitoe, while in others it is formed of EPDM. A gasket that is greater than 1 mm thick provides a more robust gasket that is not as easily dislodged or distorted by pressure differences as a thinner gasket would be, limiting the thickness to 2mm provides effective sealing without unduly distorting the volume and shape of the pump. Viton® is a synthetic rubber -4 -and fluoropolymer elastomer that is commonly used in 0-rings, while EPDM Ethylene Propylene Dien& Monomer is also a synthetic rubber.

In some embodiments, said at least one stator bore portion is formed of anodised aluminium.

The stator bore portion may be formed of a number of metals including iron, steel or aluminium, but in some embodiments it is formed of treated aluminium to increase the hardness of the stator bore which helps protect it from being damaged by the rotor where clashes occur. The treated aluminium may be anodised aluminium or it may be aluminium coated with a harder metal such as nickel. A problem with treated aluminium and in particular, anodised aluminium is that the surface is relatively rough and it is difficult to seal to. Thus, the provision of a gasket in conjunction with an anodised aluminium stator is a particularly effective way of providing a robust stator that can still seal effectively to the cover plate.

In some embodiments, said at least one cover plate is formed of non-anodised aluminium. In other embodiments the cover plate like the stator may be formed of other materials such as iron or steel.

The cover plate may not need to be hardened in the same way as the stator bore portion and as such it may be formed of non-anodised aluminium.

In some embodiments, said stator is formed as a clam shell configuration comprising two stator bore portions configured to fit together to receive said rotor, and two cover plates configured to cover said two surfaces facing away from said surfaces configured to fit together, said pump comprising two of said gaskets, each of said two gaskets being mounted between a respective one of said two cover plates and a respective one of said two stator bore portions. -5 -

A pump where embodiments are particularly applicable is a clam shell multiple stage pump, such as a multiple stage roots-type vacuum pump. In this case there will be two stator portions two, cover plates and correspondingly two gaskets.

Multiple stage roots-type vacuum pumps have interstage walls that need to be sealed with a cover plate and thus, providing a gasket between the stator bore portion and the cover plate helps provide an improved pump.

io A second aspect provides a gasket configured to seal between multiple stages of a multiple stage pump according to any preceding claim, said gasket comprising a form corresponding to a form of said stator bore portion surface and said cover plate surface, and comprising apertures for receiving components passing between said cover plate and said stator bore portion.

In some embodiments, said gasket is substantially solid, covering at least a majority of a surface of each of said pumping stages.

Having a gasket that is substantially solid as the sealing means for sealing between the cover plate and the stator bore enables it to be easily handled and to effectively seal between the interstage walls. Where the pump is a small pump the ability to have a seal that is easily handled is particularly advantageous.

In some embodiments, said gasket is between 1 and 3 mm thick.

A third aspect provides a method of servicing the pump according to a first aspect, said method comprising: removing a cover plate from a stator bore surface; removing any sealing means between said cover plate and stator bore -6 -surface; and replacing said removed sealing means with a gasket according to a second aspect of the present invention.

A gasket provides effective sealing between the cover plate and the stator bore surface and additionally is easy to handle and provides a barrier between the metal surfaces of the stator bore and cover plate impeding them from becoming adhered to each other as may occur where metal to metal surfaces meet. Thus, the provision of a gasket enables a pump to be serviced in a more straightforward way. Furthermore, existing pumps can be retro-fitted with the gasket during a io servicing operation and their original sealing means can be replaced with the gasket improving their performance.

In this regard, the gasket also provides a thermal barrier between the pump and the cover plate. This can be advantageous in some applications, for example if the pump module wants to be kept warm (to prevent sublimation of the pumped gases for example). In other applications the thermal barrier may be a problem (preventing the pump from cooling down). Gaskets of different materials with specific thermal properties can therefore be chosen to either insulate or cool the pump according to requirements of the application or pump design.

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

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

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which: -7 -Figure 1 shows a part of a clam shell stator according to the prior art; Figure 2 schematically shows a gasket according to an embodiment; Figure 3 shows a gasket according to an embodiment; Figure 4 shows a flow diagram illustrating steps in a method of servicing a pump according to an embodiment; and Figure 5 schematically shows a pump according to an embodiment.

DESCRIPTION OF THE EMBODIMENTS

Before discussing the embodiments in any more detail, first an overview will be io provided.

Embodiments provide a means of sealing between a cover plate and a multiple pumping stage stator component comprising a gasket which seals not only the outer circumference of the cover plate in the stator but also extends across the cover plate and stator surface, sealing between the interstage walls and cover plate and providing sealing between the different pumping stages within the multiple stage pump.

The gasket has a substantially solid surface with a number of apertures provided 20 to allow the required components to pass between the stator section comprising the stator bore and the cover plate. These components may include pins for fixing the two together.

The gasket may also comprise vents or pressure relief apertures which provide a 25 pressure relief path between one or more of the pumping stages and the cover plate. These may be provided to impede the gasket being sucked into the pumping chambers where it is used in a vacuum pump.

Figure 1 shows a half of a clam shell stator according to the prior art for a multiple roots-type vacuum pump. Clam shell stator 10 is formed of anodised aluminium and comprises a stator bore that has multiple pumping chambers 18 that are separated by interstage walls 14 which walls extend from the portion of the stator -8 -that receives the rotor to the opposing surface 20 to which the cover plate is attached. In this example of a prior art stator piece there is a groove 10 around the edge which accommodates an 0-ring for sealing the cover plate and the stator 10 to impede leakage of gas from the pumping chamber to the exterior.

However, there is no sealing means between the upper ends of the interstage stator walls 14 and the cover plate and arrows 16 show how fluid may leak between the stages of the pump.

Embodiments address this by applying a gasket to the upper surface of stator 10 and placing the cover plate on top of this.

Figure 2 shows the gasket 30 according to an embodiment. This gasket 30 may be formed of a flexible material such as Viton® and may cover substantially all of the surface of the pumping chambers. In this embodiment, there are apertures 40 within the gasket 30 that provide through passages for components that pass between the cover plate and the stator. These components may include fixing means for fixing the cover plate to the stator.

There may also be pressure relief apertures 42 that provide a passage between a 20 pumping stage chamber and the cover plate. These impede the gasket 30 being distorted by being sucked into the pumping chambers during operation of a vacuum pump.

Figure 3 shows an example of a gasket that has been used without these pressure vent apertures and one can see that it may become distorted.

In the example of Figure 1 the stator component 10 was formed from anodised aluminium which provides a harder surface than aluminium and impedes the rotor which is often iron from gouging burrs from the surface. One problem with anodised aluminium is that it is a difficult surface to seal to and thus, having an anodised aluminium stator can lead to increased leakage between the pumping stages where there is no additional sealing means between the cover plate and -9 -the interstage walls of the stator. Providing a gasket 30 between the cover plate and the stator impedes this leakage.

The gasket may be between 1 and 3mm wide which thickness is selected to be sufficient to stop it being pulled away from the edges and pulled into the pumping chambers.

The cover plate may be made of non-anodised aluminium and one property of aluminium is that it does have a tendency to bind to other metal surfaces when heated and thus, providing a gasket between the cover plate and the stator can impede binding between the two components and enable them to be separated more easily when servicing is required.

Figure 4 shows a flow diagram illustrating steps in a method for servicing a pump according to an embodiment. Initially at step S10 the cover plate from the stator clam shell part is removed. At step S20 any sealing means that exist between the cover plate and clam shell is then removed. Generally this will be a gasket or it may be an 0-ring or some other sealing means. At step 530 a gasket according to an embodiment is placed between the cover plate and the surface of the stator clam shell part and at step S40 the cover plate is fixed back to the stator clam shell with the gasket providing sealing between them.

Figure 5 shows very schematically how the different portions of a pump according to an embodiment fit together. The pump comprises two clam shell stator portions 10 fixed together and mounting a rotor 55 between them. There are upper and lower cover plates 50 mounted on the top and bottom of the clam shell stator portions 10 and each are sealed to the respective clam shell with a gasket 30 (shown in an exaggerated form). This gasket provides effective sealing, not only between the outer circumference of the cover plates and the clam shells but also between the cover plates and the upper surfaces of the inter-stage walls. In this way sealing between the different stages of the pump and the exterior is provided.

-10 -Although illustrative embodiments of the invention have been disclosed in detail herein, with reference to the accompanying drawings, it is understood that the invention is not limited to the precise embodiment and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope of the invention as defined by the appended claims and their equivalents.

REFERENCE SIGNS

clam shell stator piece 12 groove for receiving 0-ring 14 inter-stage walls 16 gas leakage between pumping stages 18 pumping stages stator surface to be sealed gasket apertures to allow components to pass between stator and cover io 42 pressure relief apertures cover plate rotor

Claims

-12 -CLAIMS1. A multiple stage pump comprising: a stator, said stator comprising at least one portion comprising a stator bore for receiving a rotor, said at least one stator bore portion comprising multiple inter-stage walls for forming multiple pumping stages within said stator; a rotor rotatably mounted within said stator bore; said stator further comprising at least one cover plate covering a surface of said at least one stator bore portion, said surface comprising end surfaces of said inter-stage walls; and a gasket mounted between said surface of said at least one stator bore portion and said at least one cover plate, said gasket being configured to inhibit leakage between said multiple stages by providing sealing between said inter-stage walls and said at least one cover plate.
2. A pump according to claim 1, wherein said gasket comprises a substantially rectangular form corresponding to a form of said stator bore portion surface and said cover plate surface.
3. A pump according to any preceding claim, wherein said gasket comprises apertures for receiving components passing between said cover plate and said stator bore portion.
4. A pump according to any preceding claim, wherein said gasket comprises at least one pressure relief aperture configured to provide a passage between said cover plate and at least one of said pumping stages.
5. A pump according to any preceding claim, wherein said gasket is substantially solid, covering at least a majority of a surface of each of said pumping stages.
-13 - 6. A pump according to any preceding claim, wherein said gasket is between 1 and 3 mm thick.
7. A pump according to any preceding claim, wherein said at least one stator bore portion is formed of anodised aluminium.
8. A pump according to claim 7, wherein said at least one cover plate is formed of non-anodised aluminium.
9 A pump according to any preceding claim, wherein said stator is formed as a clam shell configuration comprising two stator bore portions configured to fit together to receive said rotor, and two cover plates configured to cover said two surfaces facing away from said surfaces configured to fit together, said pump comprising two of said gaskets, each of said two gaskets being mounted between a respective one of said two cover plates and a respective one of said two stator bore portions.
10. A pump according to any preceding claim, wherein said pump comprises a multiple stage roots vacuum pump. 20
11. A gasket configured to seal between multiple stages of a multiple stage pump according to any preceding claim, said gasket comprising a form corresponding to a form of said stator bore portion surface and said cover plate surface, and comprising apertures for receiving components passing between said cover plate and said stator bore portion.
12. A gasket according to claim 11, wherein said gasket is substantially solid, covering at least a majority of a surface of each of said pumping stages.
13. A gasket according to any one of claims 11 or 12, wherein said gasket comprises at least one pressure relief aperture configured to provide a passage between said cover plate and at least one of said pumping stages.-14 -
14. A gasket according to any one of claims 11 to 13, wherein said gasket is between 1 and 3mm thick.
15. A method of servicing a pump according to any one of claims 1 to 10, said method comprising: removing a cover plate from a stator bore surface; removing any sealing means between said cover plate and stator bore surface; and replacing said removed sealing means with a gasket according to any one of claims 11 to 14.