Multi-stage vacuum pump and stator for multi-stage pump

Abstract

A multistage vacuum pump and a stator for such a pump, the stator comprising: two half-shell parts (10) defining a void for receiving two rotors and forming a plurality of pumping chambers. An outer shell (20) is arranged to surround and enclose the two half-shell parts (10) in a substantially gas-tight manner. The housing (20) has two end plates (22) configured to be mounted at either end of the two half-shell parts (10), at least one of the two end plates comprising an aperture (25) for receiving the shafts of the two rotors.

Description

Technical Field

[0001] The field of the invention relates to clamshell stators for multistage pumps and multistage vacuum pumps. Background Art

[0002] A multistage pump such as a multistage Roots pump has a clamshell stator design that enables the rotor to be placed inside the stator. The clamshell stator design consists of two stator halves separated horizontally through the centerline of the two rotor shafts. For assembly, the two rotor shafts are placed in a stator clam, and the upper stator clam is placed on top of the lower stator clam. These are bolted together to form the main pump housing. The upper and lower clams are sealed by two gaskets extending along the outside of the clams.

[0003] This design is particularly problematic for high temperature operation (>200°C). First, the gasket material needs to be able to withstand such temperatures and this tends to require expensive sealing materials such as perfluoroelastomer FFKM. Second, the seals that run the length of the clamshell utilize O-ring seals at the end covers or head plates, and the so-called T-seal junction between these two seals is difficult to seal effectively. Furthermore, in the case of pumping corrosive process gases such as fluorine, the clam may need to be plated to inhibit corrosion. Plating of the surfaces of a complex clam design with inter-chamber channels may not be simple.

[0004] It would be desirable to provide an improved stator design. Summary of the invention

[0005] A first aspect provides a stator for a multi-stage pump according to claim 1 .

[0006] The inventors of the present invention have recognized that stators formed from half-shell components (such as clamshell stators) are difficult to seal effectively, particularly at the junction between the longitudinal seals extending along the long sides of the half-shells and the O-rings between the half-shells and the end plates or head plates. The inventors of the present invention have solved this problem by providing a housing enclosing the two half-shell components and including the end plates. In use, the housing can be sealed to provide a substantially airtight environment for the half-shell stator, and therefore, a completely airtight seal along the edge of the half-shell and a completely airtight seal between the seal and the end plate are no longer required, because any gas leakage from the interior of the pump will be retained within the housing. This is particularly advantageous in the case where the pump is configured to operate at high temperatures, because providing effective and high temperature resistant seals requires the use of expensive materials. In addition, when the pump is disassembled during maintenance or after testing, these seals need to be replaced, which significantly increases the cost of the pump in the case of expensive seals. It was found that having less than 10 -3 mbar liter / second, preferably less than 10 -5Seals in housings with a standard acceptable leakage rate of mbarl / s are acceptable.

[0007] Forming a pump provided with a substantially gas-tight enclosure that seals around the pump and inhibits process gas pumped by the pump from leaking to the atmosphere, and inhibits actual atmospheric gas (such as oxygen) from leaking into the pump, may allow seals between clamshell components or between clamshell components and end plates to be eliminated or allow fewer seals of lower specification to be used. In effect, the seals on the clamshell no longer have a safety-critical function, as any gas leaks go to the sealed volume.

[0008] The housing is substantially airtight in that a pressure differential between the interior of the housing and the atmosphere is maintained when the pump is operating.

[0009] In certain embodiments, the housing defines an end and a sidewall of a discharge pumping chamber of the multi-stage pump.

[0010] Although the housing may simply enclose a conventional half-shell stator assembly defining all pumping chambers of a multistage pump, in some embodiments, the housing itself defines the ends and side walls of one or more of the end pumping chambers of the multistage pump. This arrangement may be advantageous because the end pumping chambers require ports to allow gas to enter or exit the pump. Where the housing surrounds the half-shell stator assembly defining all pumping chambers, such ports then need to pass through the housing wall and through the half-shell stator wall in order to reach the pumping chambers, and this may present problems with port alignment and gas leakage. A particularly clever solution to this problem is to use the housing to define at least some of the walls of one or both of the end pumping chambers, thereby allowing ports to pass through the housing and into the end pumping chambers.

[0011] In certain embodiments, the housing is formed from a plurality of sections arranged such that a junction between adjacent sections is between two sections that are sealed together in a substantially airtight manner using a single sealing surface.

[0012] Forming the housing in two or more parts allows the pump to be assembled by mounting the half-shell components within the housing. The housing parts are sealed together to provide an airtight housing. The seal between at least two parts of the housing can be located in a position that facilitates the sealing function.

[0013] Having an outer shell allows greater flexibility in choosing the configuration of the multiple parts, and allows choosing the location of the junctions between the parts that need to be sealed. In particular, the configuration can be chosen so that any junction is between no more than two adjacent parts. This allows the sealing surface between the two parts to be a single sealing surface that can be sealed with a single seal, and avoids problems that arise where there may be three or more parts that intersect and there is a junction between the seals (such as at the end of a conventional clamshell stator) where there is a T-seal between the longitudinal seals between the clamshells and the O-rings between the shell and the end plate.

[0014] It may be advantageous to place the seal between the surfaces of the different parts of the housing at a location on the machine where it is easier to achieve the seal. For example, where the pump is configured to operate with a high temperature discharge device, a seal location closer to the cooler inlet may be selected.

[0015] Providing a housing around the clamshell provides greater flexibility in where the seal may be placed and allows selection of a location that facilitates the sealing function, which location may vary depending on the configuration of the pump.

[0016] In certain embodiments, at least a portion of one portion of the housing is integral with one of the half-shell components and at least a portion of a second portion of the housing is integral with the other of the half-shell components, the housing portion having a different form than the half-shell components.

[0017] In some embodiments, the housing may not be a separate housing, but may be integral with the half shell components, but have a different shape. The different shape allows the sealing surface to be located at a different position than the sealing surface between the two half shell parts, which may eliminate T-shaped seals.

[0018] In certain embodiments, the housing is formed from cooperating wedge-shaped portions.

[0019] The wedge-shaped portions allow corresponding inclined surfaces to form sealing surfaces that can be sealed using O-ring components.

[0020] In some embodiments, the housing has windows in the end plates that allow the rotor to be placed into the lower portion of the housing. These windows will be filled with plates that include apertures for receiving the rotor shaft. In other embodiments, there may be no windows and the rotor may fit within the housing and have stub shafts attached to them after assembly.

[0021] In other embodiments, the housing is attached to at least a portion of the two half-shell components by at least one of a sealing material and an adhesive material.

[0022] Where the housing is of similar dimensions to the half shell component, the housing may be adhered to the half shell component by an adhesive material, or there may be a sealing material between them to hinder leakage of process gas from the pumping chamber within the half shell component. In other embodiments, where the housing is a close fit to the half shell component, there may be an interference fit between the two. This latter may make it more difficult to disassemble the machine during maintenance.

[0023] In other embodiments, there is a gap between the outer shell and the two half-shell parts.

[0024] An alternative solution may be to construct the housing so that it is mounted at a distance from the two half shell parts with a gap between them. This gap provides a thermal break so that in the event that the pump is operated at high temperatures, the housing is kept at a lower temperature, providing a safer environment for the engineer, and also allows the sealing material that seals the parts of the housing to be made of a material with a lower heat resistance than would otherwise be possible. The gap may be greater than 0.5 mm, preferably greater than 1 mm.

[0025] In certain embodiments, the housing includes a larger box portion and a cover portion, the cover portion sealing an aperture in the box portion that is large enough to receive the two half-shell components.

[0026] One arrangement of the housing may be such that it comprises a box type arrangement with an open top that is large enough to receive the half shell stator components, the housing comprising a cover sealed to the box portion. In such an arrangement, the shaft of the rotor may be configured to receive a stub shaft at either end so that once the rotor is mounted within the half shells within the housing, the stub shaft may be inserted through an aperture in the end plate of the housing.

[0027] In certain embodiments, the housing comprises two parts, each part comprising the end plate and one of the substantially cylindrical side walls extending from the end plate, the substantially cylindrical side walls of the two parts being configured to seal together to form the housing.

[0028] One arrangement of the housing may be such that it comprises two parts, each comprising an end portion and a side wall, and arranged to seal at the side wall. The two parts may in certain embodiments be symmetrical and substantially cylindrical.

[0029] In certain embodiments, the housing includes a central portion and two end portions, each end portion including the end plate and one of a side wall extending from the end plate, the side wall being configured to seal to the central portion.

[0030] Alternatively, the housing may include a central portion and two end portions having side walls attached to the central portion. In some embodiments, the central portion may be substantially cylindrical. This requires additional seals, but may be easier to manufacture.

[0031] In certain embodiments (due to the housing), there are no seals disposed between the end plates and the half shell components. For example, at least the O-ring seals between the end plates and the half shell components are omitted. In this way, the problematic T-seals of previous designs (where the longitudinal seals and O-ring seals meet between the half shell components) are avoided.

[0032] In certain embodiments, at least one of the half-shell components comprises a plurality of ports, each comprising an opening of a gas delivery passage in an outer surface of the at least one half-shell component, the gas delivery passage extending from the outer surface of the at least one half-shell component to a portion of the void forming one of the plurality of pumping chambers, the housing enclosing the ports and containing the gas delivery passage.

[0033] The passages between the pumping chambers typically extend within the half shell components and are thus formed during casting. Multistage pumps may be used to pump corrosive process gases and therefore it may be advantageous to coat the surfaces of the stator components that contact the process gases with an anti-corrosion coating. In this regard, the half shell components of the stator are typically made of cast SG iron and in order to be successfully plated or coated, the surfaces should be machined. In the case of internal passages within the components, machining is not feasible. Changing the design to have ports to the passages in the outer surface of the clam shell improves access to the gas delivery passages for machining and allows machining and therefore successful coating of the surfaces exposed to the process gases.

[0034] Indeed, providing a housing around the half-shell components provides the opportunity to extend the passages between the pumping chambers outside the half-shell components and, therefore, allows machining of ports from these pumping chambers.

[0035] In certain embodiments, a surface of the half-shell component configured to contact the gas during pumping is coated.

[0036] As previously mentioned, the gas pumped by the multi-stage pump may be a process gas, which may be corrosive. Coating the surfaces that contact the gas will protect them from these gases. In certain embodiments, the surfaces that contact the gas are processed, and this allows for efficient coating and provides improved stator components.

[0037] In certain embodiments, the end plate comprises a head plate.

[0038] The head plates of the pump mount bearings for supporting the rotor. In some embodiments, these head plates are part of the housing that form the end plates of the housing, while in other embodiments they may be separate from the housing. Where the housing forms part of the inlet pumping chamber and / or the discharge pumping chamber, then having the head plates separate from the housing provides a thermal break between the housing and the head plates, thereby allowing the bearings to be maintained at a cooler temperature.

[0039] A second aspect provides a multi-stage vacuum pump comprising a stator according to the first aspect and two rotors installed in the stator.

[0040] In certain embodiments, the vacuum pump includes one of a Roots-type pump or a claw pump.

[0041] 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 different from those explicitly set out in the claims.

[0042] Where an apparatus feature is described as being operable to provide a function, it will be appreciated that this includes apparatus features providing that function or being adapted or configured to provide that function. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Embodiments of the present invention will now be further described with reference to the accompanying drawings, in which:

[0044] Figure 1A Schematically shows a cross-sectional view of a stator for a multi-stage pump according to an embodiment;

[0045] Figure 1B The clamshell and rotor of such a pump are shown;

[0046] Figure 2 shows the stator of Figure 1 with the housing cover in place;

[0047] Figure 3A A cross-sectional view of the rotor is shown showing a central hole for receiving a shaft;

[0048] Figure 3B Figure 1 and Figure 2 A multistage pump with a stator and shaft and head plate in place;

[0049] Figure 4A shows a cross-sectional view of a multi-stage vacuum pump according to a second embodiment;

[0050] Figure 4B shows a top view of a multi-stage vacuum pump according to a second embodiment;

[0051] Figure 4C shows an overview of a multi-stage vacuum pump according to a second embodiment;

[0052] Figure 5 shows an overview of the assembled clamshell components of a stator according to an embodiment without the housing in place;

[0053] Figure 6 Another embodiment of a stator for a multi-stage pump is shown; and

[0054] Figure 7 An alternative embodiment of a stator for a multi-stage vacuum pump is shown. DETAILED DESCRIPTION

[0055] Before discussing the embodiments in more detail, an overview will first be provided.

[0056] Embodiments provide a multistage pump having a clamshell assembly housed within a hermetically sealed housing. The housing is formed in two or more sections, and the seal between the two or more sections does not extend parallel to the junction between the two clamshells, and in some embodiments extends substantially perpendicular to the junction. This reduces and in some cases eliminates the need for gaskets or sealants between the clamshell halves, and also eliminates the need for a hot "T" seal between the longitudinal seal and the O-ring seal.

[0057] Certain embodiments have channels in the outside surface of the clamshell member that, when surrounded by the housing, form gas transfer passages between pumping chambers of the multi-stage pump. This allows the gas transfer ports between the pumping chambers to simply extend through the clamshell, providing a fluid communication path from the pumping chamber to the passage between the outside surface of the clamshell and the inside surface of the housing. The geometry allows these ports and transfer passages to be machined, and these machined surfaces can be effectively coated and thereby protected from the corrosive gases being pumped.

[0058] Certain embodiments have a gas delivery passageway that is substantially inside the clamshell member but has openings in the outside surface of the clamshell member. These openings provide access to process all surfaces of the gas delivery passageway and ports that communicate between the passageway and the pumping chambers of the multi-stage pump. The housing closes the openings in the outside surface of the clamshell member and isolates the gas delivery passageways from each other, in this way covering the surfaces that form the gas delivery path between the pumping chambers.

[0059] Figure 1A A stator for a multi-stage pump according to an embodiment is shown. The stator comprises two clamshell components 10 enclosing the pumping chamber and rotor of the multi-stage pump. Figure 1B It is shown how the two clamshells 10 are assembled to hold and enclose the rotor 32 .

[0060] The clamshell 10 is mounted within a housing 20 which in this embodiment is formed in two parts, including a main housing 22 having a base and end panels or end pieces, and a cover portion 24 which is provided at the bottom of the housing. Figure 1A The cover 24 is sealed to the main box in a substantially gaseous type manner, thereby forming the housing 20, so that when the pump is in operation, there is a pressure difference between the interior of the housing and the atmosphere. In this regard, the interior of the housing is at an intermediate pressure between the lower pressure in the vacuum pump and the atmosphere. In effect, the vacuum pump or vacuum generator is contained in a substantially airtight outer container. This allows the seals between the clamshells and in particular the seals between the clamshells and the head plate to be dispensed with, or allows the seals, if retained, to be less critical to safety and therefore of a lower specification.

[0061] The T-seal that was conventionally between the longitudinal seal that sealed the clamshell and the O-ring that sealed the clamshell to the head plate was always a difficult seal to provide in a gas type manner and no longer exists.

[0062] The seals for hermetically sealing the housing are located at locations that depend on the construction of the housing, and therefore, with appropriate design, these seals may be of a more convenient form and T-shaped seal junctions between seals may be avoided. In this embodiment, the seals are provided between the cover 24 and the main tank portion of the housing 20. There is an inlet 40 extending through the housing from the clamshell and a discharge device 42 extending likewise. There are apertures in the end pieces 22 of the housing that allow the shaft of the rotor to extend outwardly from the pump. In this regard, in certain embodiments, the shaft may be cantilevered and then there may be an aperture 25 on only one end piece.

[0063] The shaft is supported on bearings which in some embodiments are incorporated into the end pieces of the housing. In other embodiments, the bearings are incorporated into a separate head plate 62 which is sealed to the housing. There may be a seal 64 around an aperture 65 in the head plate 62 which receives the rotor.

[0064] Figure 2 The stator of FIG. 1 is shown with the cover 24 in place, thereby forming a hermetically sealed housing 20 .

[0065] Figure 3A Shows the installation Figure 3BAn example of a rotor in a pump shown in FIG. 1 is a schematic diagram of a pump having a plurality of rotors disposed in a plurality of embodiments. In this embodiment, the rotor is a shortened rotor with a hole through it. The rotor is mounted in a clamshell and the clamshell is placed within the housing before a longer shaft is inserted through the hole. Once the rotor is in place, the shaft can be pushed through the rotor with the hole and positioned at either end using an expansion device to lock it into the rotor. Once the shaft is installed in both rotors, another sleeve can be used to increase the diameter of the shaft from the outside to the housing so that the assembly resembles a typical clamshell design.

[0066] An alternative design would be to use a stub shaft in a shortened rotor, wherein the rotor would be mounted in a clam shell and the clam shell mounted within the housing before the stub shaft was pressed into either end of the shortened rotor.

[0067] Figure 3B The housing 20 is shown with a head plate 62 supporting the rotor shaft 30 attached to the end plates 22 or a surface of the housing 20. The head plate 62 includes bearings within apertures that support the rotor shaft, allowing it to rotate when driven by the motor.

[0068] As described above, the shaft of the rotor has been shortened and may have a hole through the bottom surface to receive a short shaft rod, or a through hole to receive the entire shaft rod, allowing the rotor shaft to be assembled in the clamshell, and then the clamshell is placed in the housing, and then the head plate is attached without the shaft protruding. No O-ring is required at the end of the clamshell 20, because this end is now inside the housing 20. The housing can be a cast housing, and the clam portion can be located in the housing by locating pins. The discharge device and the inlet are sealed to the housing. O-rings and grooves are used to seal the head plate 62 to the housing 20. The cover 24 is fixed and sealed to the edge of the main box portion of the housing and to the inlet 40.

[0069] FIG. 4A to FIG. 4C An alternative embodiment is schematically shown in which the housing is formed of two parts that meet at a sealed junction 28 around the clamshell 10. The junction can be sealed by an O-ring, where the clamshell has a circular cross-section. In this embodiment, the inlet pumping chamber 44 and the exhaust pumping chamber 46 have outer walls formed by the housing 20, and this allows the inlet port 40 and the exhaust port 42 to provide access through the housing directly to these pumping chambers without also having to travel through the clamshell wall, which would require precise alignment of the clamshell with the housing and additional sealing. The intermediate pumping chamber is formed by the clamshell in a conventional manner and has a passage 15 that allows gas to travel between them.

[0070] In this arrangement, the housing 20 can be viewed as an inlet and discharge stage hopper that meet at a single flange towards the middle of the pump sealed by an O-ring 28. An alternative embodiment (not shown) would have shorter inlet and outlet hoppers that each seal to a center tube. In this case, the housing would have three sections: an inlet section and a discharge section that form part of the inlet and discharge pumping chambers, and a central cylindrical section. This would require additional seals so that there would be two O-ring seals, but would avoid the need to create deep holes in the end hoppers and would therefore be likely to be easier to manufacture.

[0071] Figure 4B A top view is shown showing two rotor shafts 30, and Figure 4C An overview of the exterior of the assembled pump is shown. In certain embodiments (not shown), the housing may be configured with retractable cooling plates arranged to contact and cool the exterior surface of the shell 20 .

[0072] Figure 5 A similar design is shown without the housing in place so that the interstage ports 15 providing gas transfer between pumping chambers are visible. With suitable sealing means between the clamshell 10 and the housing, gas transfer passages between pumping chambers via adjacent ports 15 are provided. This design allows the ports to be machined without the need to cast the ports and passages. The machined surface is easier to coat or plate, which allows the clamshell to be protected from the aggressive process gases being pumped.

[0073] Figure 6 An alternative cylindrical design is shown that is similar to the design of Figure 4, but in which there are three sections: two end sections including end plates 22 and a cylindrical middle section. The end sections are sealed at either end via O-ring seals with the cylindrical section 22. Thus, no T-seals are required because the O-ring seals surround the outer perimeter of the end pieces and do not span the junction between the clam shells.

[0074] Figure 7 An alternative design is shown in which the clamshell member 10 is integral with the housing 20. In this embodiment, the housing 20 is formed of two half wedges, each housing a half clamshell. The seal between the two halves therefore runs along the edge between the two wedges. The end plate 22 incorporates a window at the end of the wedge which accommodates the shaft 30 to allow the rotor to be positioned at an angle. A separate head plate covers the window and contains the bearings that support the rotor shaft. Alternatively, the shaft rod can be inserted into the rotor shaft once it is in the stator, in which case no large window is required and the bearings can be incorporated into the end pieces of the housing.

[0075] A continuous O-ring seal (not shown) is provided between the two parts of the wedge-shaped housing 20 and this avoids the need for a T-section seal which is difficult to achieve between the two clam halves and the head plate. In this embodiment, the end plate 22 may comprise a head plate.

[0076] Although illustrative embodiments of the present invention have been disclosed herein in detail with reference to the accompanying drawings, it is to be understood that the present invention is not limited to the specific embodiments and that various changes and modifications may be implemented therein by those skilled in the art without departing from the scope of the present invention as defined by the appended claims and their equivalents.

[0077] Reference numerals

[0078] 10 Clamshell stator

[0079] 15 Interstage Ports

[0080] 20 Outer shell

[0081] 22 End plate

[0082] 25 Port for receiving rotor

[0083] 28 Outer housing seal

[0084] 30 Rotor shaft

[0085] 32 Rotor

[0086] 40 Entrance

[0087] 42 Discharge device

[0088] 44 Inlet pumping chamber

[0089] 46 Drain pumping chamber

[0090] 62 Headboard

[0091] 64 O-ring

[0092] 65 Rotor shaft support

Claims

1. A stator for a multistage pump, the stator comprising: two half-shell members defining a void for receiving the two rotors and forming a plurality of pumping chambers; two end plates mounted at either end of the two half-shell parts, and at least one of the two end plates includes an aperture for receiving the shafts of the two rotors; as well as a housing which surrounds and encloses the two half-shell parts in a substantially airtight manner, wherein: The two end plates form part of the housing; and The housing defines one end and a side wall of an inlet pumping chamber of the multi-stage pump.

2. The stator according to claim 1, wherein: The housing defines one end and a side wall of a discharge pumping chamber of the multi-stage pump.

3. A stator according to any preceding claim, wherein: The housing is formed from a plurality of parts arranged such that a junction between adjacent parts is between two parts that are sealed together in a substantially airtight manner using a single sealing surface.

4. The stator according to claim 3, wherein: The housing is formed from two parts.

5. A stator according to any preceding claim, wherein: At least a portion of one portion of the housing is integral with one of the half-shell components and at least a portion of a second portion of the housing is integral with the other of the half-shell components, the housing portion having a different form than the half-shell components.

6. The stator according to claim 5, wherein: The housing is formed from cooperating wedge-shaped portions.

7. The stator according to any one of claims 1 to 4, wherein: The housing is attached to at least a portion of the two half-shell components by at least one of a sealing material and an adhesive material.

8. The stator according to any one of claims 1 to 4, wherein: The housing is mounted at a distance from the two half-shell parts so that there is a gap between the housing and the two half-shell parts.

9. The stator according to any one of claims 1 to 4 or 7 or 8, wherein: The housing includes a larger box portion and a cover portion that seals an aperture in the box portion that is large enough to receive the two half-shell components.

10. The stator according to any one of claims 1 to 4 or 7 or 8, wherein: The housing comprises two parts, each part comprising the end plate and one of a substantially cylindrical side wall extending from the end plate, the substantially cylindrical side walls of the two parts being sealed together to form the housing.

11. The stator according to any one of claims 1 to 4 or 7 or 8, wherein: The housing includes a central portion and two end portions, each end portion including the end plate and one of side walls extending from the end plate, the side wall being sealed to the central portion.

12. A stator according to any preceding claim, wherein: There are no seals arranged between the end plate and the half-shell parts.

13. A multi-stage vacuum pump comprising a stator according to any preceding claim and two rotors mounted within the stator.

14. The multi-stage vacuum pump according to claim 13, wherein: The vacuum pump includes one of a Roots-type pump or a claw pump.

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