JP2015509165A - pump - Google Patents

Abstract

The present invention relates to a multi-stage vacuum pump (10) having a plurality of pumping (suction / discharge) stages (12, 14, 16, 18). The vacuum pump includes a stator that forms a corresponding pumping chamber (32, 34, 36, 38) of each pumping stage, and a plurality of rotors (44a, 44b; 46a, 46b; 48a, 48b; 50a, 50b). And at least one shaft (40, 42), each rotatably supported in a corresponding pumping chamber. The stator extends over the axial extent of the plurality of stator stages, thereby enclosing the at least one shaft and forming an internal contour of the plurality of stator stages, and corresponding pumping And a plurality of lateral walls (22, 24, 26, 28, 30) provided on each axial side of the stator stage to form a chamber. At least one of the lateral walls is an interstage (26, 28, 30) located between the stator stages so that the stator envelope can be arranged radially inward of the stator portion. It is comprised so that the step part may be surrounded.

Description

  The present invention relates to a multistage vacuum pump and a stator of such a pump.

  The vacuum pump may be formed by a positive displacement pump, such as a Roots pump or a claw pump, having one or more pumping (suction and discharge) stages connected in series. Multi-stage pumps are desirable because they require less manufacturing and assembly time compared to multiple pumps connected in series.

  Multi-stage roots or claw pumps are typically manufactured and assembled in one of two common forms, i.e., as a stator stack or clamshell.

  A pump 110 with a stator stack structure is shown in FIG. The pump 110 has a plurality of pumping stages 112, 114, 116, 118. Each pumping stage has a rotor structure (not shown) and a stator structure 120, 122, 124, 126 for pumping fluid from the inlet to the outlet of each stage. The outlet of one pumping stage is in fluid communication with the inlet of an adjacent downstream stage so that the compression achieved by this pump is the cumulative result of each stage. Interstage structures 128, 130, 132 are positioned between adjacent pumping stages. These interstage structures separate the pumping chambers of adjacent pumping stages from one another and carry fluid from the upstream pumping stage outlet to the downstream pumping stage inlet. Two head plates 134, 136 are located at each end of the pumping stack. The head plate separates the pumping chambers of the most upstream pumping stage and the most downstream pumping stage, respectively, from other components of the pump, such as gears and motors, and fluids of the first pumping stage. Carry into the inlet or out from the outlet of the first pumping stage. Thus, the pump is made up of a plurality of separate layers that are stacked together to form the pump. Lamination can suitably be accomplished by fastening one or more anchor rods with fasteners, such as bolts, through holes provided in each of the layers. In the present specification, the stator structure is referred to as a stator slice, and the interstage structure is simply referred to as an interstage part.

  A cross section of the pump 110 is shown in FIG. A rotor structure is shown in FIG. 11, which has a plurality of rotor stages 138, 140, 142, 144, each rotor stage in this example being a pair of cooperating rotors A, B. Consists of. Only the rotor of the first rotor stage 138 is indicated by the symbols A and B in order not to overfill the reference numerals in the drawing. The rotor A is rotatably supported by the shaft 146, and the rotor B is rotatably supported by the shaft 148. As the rotor stage rotates, fluid is pumped from the stage inlet to the stage outlet, so that fluid is pumped through these stages from the pump inlet (IN) to the pump outlet (OUT). It has become.

  During assembly, the individual components of the pump are stacked together in order. The first head plate 134 and the shafts 146 and 148 are assembled. Stator stage 120 is applied to head plate 134 and is typically positioned in place with a dwell or mating pin. One or both of the head plate and the stator stage may have an annular groove that receives an O-ring for sealing the interface between the head plate and the stator stage. The rotor 112 may be fitted on a shaft, and the rotor 112 may have a keyed structure for placing the rotors in the correct position. Next, the interstage 128 is again attached to the stator stage 120, typically by the use of a dwell, which includes an O-ring for sealing between the interfaces. The remainder of the pump stack may be assembled in a similar manner and the stack clamped to resist axial movement between components. In some configurations, each interstage is integral with an adjacent stator stage, and this integral component is similarly assembled as described above. Also, as will be apparent, the pumps may be assembled in a different order, for example, the head plate may be attached last.

  In an alternative configuration, the stator component may have two of the above-described stator components, eg, portions 122, 130 that may be integral, provided that such integral component has no more than one interstage. The condition is that the part is formed.

  The axial clearance or clearance between the rotor and the interstage or head plate must be accurately controlled. This is because otherwise the pumped fluid may leak from the low vacuum region of the pumping chamber through the axial clearance into the high vacuum region. Even if the component is precisely machined, it is inevitable that the form of the component will vary, thereby allowing a potentially increased axial clearance between the rotor and the interstage or head plate. It is necessary to give errors to the pump design. Pump stacks present the problem of cumulative tolerances introduced by each of the many interfaces between components. In the illustrated pump, there are eight such interfaces. Therefore, the relative placement of the rotor and the interstage or head plate cannot be accurately controlled, thereby causing pumped fluid leakage or contact between the rotor and the interstage or head plate. Will be understood.

  As a result of component size variations, excessive clearances or improper clearances that can result in seizures may occur. Increasing the nominal clearance to eliminate the risk of seizure increases the risk of excess clearance and reduced vacuum performance due to this. As a result, additional pumping stages may be required, associated with increased complexity and cost.

  In addition, since each interface requires a seal, many interfaces require many seals, each of which is a potential source of leakage. The seal may not be able to be assembled correctly, the O-ring will deteriorate over time due to chemical erosion, and any imperfect sealing surface that abuts the O-ring will all cause the seal to deteriorate It becomes.

  The requirements for O-rings increase the cost of the pump and add additional machining for the O-ring groove. Dwells and dwell holes also cause increased manufacturing costs.

  A modified stator stack structure is disclosed in EP 0480629. This patent document discloses a stack of stator portions 16 end to end joined together. The interstage portions 17 are disposed on the radially inner side of the corresponding stator portions. The outer peripheral part of the interstage part and the axial interface between the stator parts are sealed by O-rings. This structure suffers from many of the disadvantages of the stator structure described in detail above. The interface between the stator portions requires sealing and mutual fastening to prevent pumped fluid from escaping from the pump. Also, the accumulation of axial tolerances is inevitable, which limits the ability to design an accurate pump.

  Another pump structure has a so-called clamshell as shown in FIG. The pump 150 has two stator portions or shells 152, 154. The stator portion 154 is shown in detail in perspective in the drawing, and the stator portion 152 has a corresponding configuration. The stator portion 154 includes head plates 164 and 166 and interstage portions 168, 170, 172, 174, and 176, and these headplate portions and interstage portions together with the portion 152, the stator stages 155 and 156. , 157, 158, 159, 160 are formed. The head plate and interstage have recesses 178 that receive two shafts that support the rotor when assembled.

  During assembly, the rotor and shaft (not shown) are joined as indicated by the arrows in FIG. 12, and they are placed in place with a dwell and then sealed and clamped so that the pump is Form. The interface 174 between the first stator portion and the second stator portion is typically sealed with a gasket or sealant that is inherently less resistant to leakage than the O-ring described above.

European Patent No. 0480629

  The radial spacing or tolerance between the rotor and stator stage is tightly controlled so that the rotor can effectively sweep the inner surface of the pumping chamber and resist fluid leakage beyond the rotor as it rotates. Need to be done. For clamshell stators, the radial tolerance is large because the stator profile cannot be machined as easily or accurately as the stator stack bores. In addition, axial tolerances are necessary if there is a potential misalignment between the two stator halves.

  The present invention provides an improved vacuum pump.

  The present invention is a multi-stage vacuum pump comprising a stator that forms a plurality of pumping chambers and at least one shaft that rotatably supports a plurality of rotors in the corresponding pumping chambers. Is provided between the integral stator envelope surrounding a plurality of axially adjacent pumping chambers provided around the shaft and between the pumping chambers radially inward and axially adjacent to the stator envelope. And providing a multistage vacuum pump having at least one interstage lateral wall.

  The present invention also provides a stator for a multi-stage pump.

  In order that the present invention may be better understood, several embodiments of the invention will now be described which are given by way of example only with reference to the drawings.

It is a schematic sectional drawing of a multistage vacuum pump. FIG. 2 is a radial cross-sectional view taken along the line II-II in FIG. 1. FIG. 2 is a simplified view of the stator portion shown in FIG. 1. FIG. 4 is a diagram (a, b, c) showing a modified stator part during assembly together with a rotor and a lateral wall. FIG. 6 shows another improved stator portion and lateral wall. It is a figure (a, b, c, d) which shows the method of the fastening of the horizontal direction wall to a stator part. FIG. 5 shows another way of fastening the lateral wall to the stator part. It is a figure which shows the interstage horizontal wall in detail. It is sectional drawing of a remodeling type pump. It is an enlarged view of a fixed structure. It is a figure which shows the vacuum pump which has a stator stack structure. It is sectional drawing of the vacuum pump shown by FIG. It is a perspective view of a clamshell type vacuum pump.

  Referring to FIG. 1, a multi-stage vacuum pump 10 is shown having a plurality of pumping stages 12, 14, 16, 18. In this example, four pumping stages are provided, but it is possible to provide two, three or more pumping stages depending on the requirements. The pump has a stator that includes components 20, 22, 24, 26, 28, 30 that form respective pumping chambers 32, 34, 36, 38 of the pumping stage. FIG. 1 shows a Roots or Claw pump provided with two shafts 40, 42, which have a plurality of meshing rotor pairs 44a, 44b, 46a, 46b, 48a, 48b, 50a and 50b are rotatably supported in the corresponding pumping chambers 32, 34, 36 and 38, respectively. Other types of pumping mechanisms such as a rotary airfoil pump with a single shaft that supports a single rotor within each pumping chamber are within the scope of the present invention.

  As shown in FIG. 1, the stator has an integral stator portion or envelope 20 that surrounds the axial shaft and forms a step profile 52 of a plurality of stator stages. This configuration should be distinguished from known stator stack configurations where the stator portion surrounds the shaft but defines the inner profile of only one stator stage. Similarly, the configuration of the present invention is a known clamshell configuration in which the stator portion extends only partially around the shaft and the stator portion has a profile that forms part of a plurality of pumping chamber stator stages. Should be distinguished.

  Reference is also made to FIG. 2, which is a radial cross-sectional view of the pump of FIG. 1 taken along the line II-II through the pumping stage 16. It will be appreciated that the pumping stages 12, 14, 18 have substantially the same cross section. The stator portion 20 constitutes an inner contour shape 52 of each of the four stator stages. In use, the stator stage step profile 52 is swept by the rotors 44-50 during rotation. A slight clearance between the radial end of the rotor and the internal contour 52 is maintained to allow expansion during use. The outer contour shape 54 of the stator portion 20 may be of any suitable shape, for example a block. Preferably, however, the outer profile is relatively thin so that heat can be removed from the pumping chamber, in which case the outer profile 54 may be approximately the same as the inner profile.

  Referring again to FIG. 1, a plurality of lateral walls 22, 24, 26, 28, 30 are disposed on each axial side of the stator stage to form pumping chambers 32, 34, 36, 38. The lateral walls 22, 24 are so-called head plates arranged at the axial ends of the stator part. One of the head plates may be formed integrally with the stator portion 20 if necessary. The axial walls 26, 28, 30 are so-called interstage parts because they are arranged between two adjacent stator stages. The stator portion 20 is configured to surround the lateral walls 26, 28, 30 so that the lateral walls 26, 28, 30 can be disposed radially inward of the stator portion. The fixing means 56 fixes the interstage part at a fixed position. The present invention relates to a multistage pump having two or more stages, and in a pump having only two stages, only one interstage is required to be arranged radially inward of the stator portion 20 .

  Unlike the clamshell configuration described above, where each stator portion extends about an axis or extends only about 180 ° about the axis, the stator portions surround one or more axes of the pump and extend over 360 °. Yes. In addition, the stator portion comprises a plurality of stator stages, which together with one or more interstages form a plurality of pumping chambers. This configuration differs from the above-described stator stack configuration in which the stator portion surrounds the pump axes and extends through 360 °, but each stator stage comprises only one stator stage.

  Accordingly, the stator portion or enclosure has an internal cavity that extends longitudinally or axially, the internal cavity extending partially or completely through the enclosure. FIG. 3 shows the cavity 64 of the stator portion 20 with the other parts of the pump omitted for clarity. The head plate placement location 60 and the interstage placement location 62 are shown in dashed lines. Molded portions or feature portions 58 are shown, and the interstage portions can be fixed at these molded portions or feature portions, which will be described in detail below. As shown in FIG. 3, the cross section of each of the stator stages is generally uniform, and the cross section from one stage to the next is also uniform. Accordingly, the interstage is generally of substantially the same size and shape.

  In the modified configuration example shown in FIG. 4, the cross section of each stage may be uniform, but is different from one stage to the next. The stator stages are larger in volume or bulk toward the right side of the figure, and these stator stages are typically pump transport stages upstream of the pump. FIG. 4 schematically shows the three manufacturing stages of the pump. In FIG. 4a, the stator portion 20 is shown with two interstages 26, 28 in an unassembled state. In the partially assembled state of FIG. 4b, one or more first rotors 44 are inserted into the internal cavity 64 and in place on one or more shafts (not shown). Has been placed. The first interstage 26 is then inserted into the cavity and locked in place. The one or more second rotors 46 are then placed in place on the shaft and the second interstage 28 is inserted into the cavity 64 and locked in place. In the fully assembled state of FIG. 4 c, one or more third rotors 48 are locked in place on one or more shafts and the head plates 22, 24 are at the axial ends of the stator portion 20. It is fixed at a fixed position.

In yet another variation, the axial spacings A ¹ , A ² , A ³ , A ⁴ , and A ⁵ (FIG. 5) between adjacent lateral walls are equal to one stator stage and the next depending on pumping requirements. The stator stage may be different. In one example, the interstage portion may be located at a predetermined molded portion of the stator portion as described above. In this regard, the securing means is configured to locate and secure at least one, preferably all, of the interstage portions at any selected location along the axial extent of the stator portion. The interstage portions are tightly fitted inside the stator 20, and the interstage portions may have a radially outer peripheral portion including a sealing material that is in close contact with the inner surface of the stator 20.

  In another example, as shown in FIG. 5, the location of the interstage in the stator portion is not predetermined and may be selected in the field by operative assembly of the pump. When selecting the location of the interstage part during assembly, it is possible to eliminate some of the clearance for manufacturing variations of the rotor and stator components from the clearance, thus improving machine performance without increasing manufacturing costs. Can be improved. In this regard, one or more interstages may be arranged to float between adjacent rotors. The floating interstage is not fixed to the stator and can move freely in the axial direction. Angular movement of the interstage is prevented by the complementary shape of the interstage and the inner surface of the stator. Axial motion is limited by the axial end of the rotor located adjacent to the floating interstage. Preferably, the interstage and the axial end of the rotor are coated with a lubricant to reduce the rotational resistance of the rotor and reduce frictional heat. This configuration allows further reduction of the required total axial clearance. This is because the floating interstage is not fixed to the stator envelope but is positioned in place by the adjacent rotor, and most of the space for thermal expansion can be removed from the pump clearance. Because.

  FIG. 6 shows the configuration of the fixing means 56 shown in FIG. 1 in detail. FIG. 6A is a diagram in which an enlarged portion of the portion VI shown in FIG. 1 is viewed in the tangential direction, and FIG. 6B is a diagram in which the same portion is viewed in the axial direction. 6c and 6d show the fastener 58 before installation.

  The fastener 58 has a fixing portion 66 that can insert the interstage portion 26 into the stator portion 20 in the first state, and can fix the interstage portion in a fixed position in the second state. ing. The head portion 68 is operable to move the fixed portion between the first state and the second state. The fixed part has a partially arcuate flange, preferably having a tapered thickness. The stator portion 20 is formed in an inner contour shape 52 and has an undercut groove 70 that receives the fixed portion in the second state. The interstage part 26 has a cavity 72 for receiving a fastener. The cavity opens radially outward so that the arcuate flange can protrude from the interstage when the flange is in the second state and the operator can insert the tool into the head portion for work. It opens in the axial direction so that it can be done. The head portion is shaped to receive a complementary shaped tool that rotates the fixed portion between the states described above.

  Preferably, at least three fasteners 58 are provided around the perimeter to secure the interstage to the stator portion.

  In use, the interstage 26 is inserted into the stator portion while the fixed portion 66 is in the first state. A lip 78 extending radially inward from the inner contour 72 of the starter portion may be provided to position the interstage. When in place, a tool is used to rotate the fastener 58 or the flange of each fastener 58 so that the fastener protrudes into the undercut groove 72 of the stator portion 20. The thinnest part of the flange enters the groove first and continues to rotate, so that the thicker part of the flange is positioned on the axial faces 74, 76 of the groove to accurately position the interstep and lock it in place. Engage.

  In another fixed configuration example shown in FIG. 7, a closed bore 80 is formed at an oblique angle with the inner contour shape 52 of the stator portion 20. A through-bore 82 is formed in the interstage portion so as to extend obliquely from the axial end face to the periphery of the interstage portion in the radial direction. The fastener is inserted into the aligned bores 80, 82 to fix the interstage portion in place. One or both of the bores 80, 82 may be threaded to receive the threaded fastener 58. Fastening of the fastener into the threaded bore may be performed to expand the interstage to a slight extent and apply it to the inner wall of the stator, thereby improving the sealing.

  In yet another configuration example, the interstage portions may be interference fitted to secure the interstage portions in place within the stator envelope. In this case, the stator envelope does not need to be provided with a fixed molding portion, and the stator envelope may have a smooth inner surface. As a modification, the inner surface may be provided with an annular lip for positioning the interstage portion in place prior to fixing. During assembly, the interstage is made of a material that causes thermal expansion, such as a metal or metal alloy. Prior to insertion into the stator envelope, the interstage is cooled by any suitable means so that the interstage shrinks. Preferably, the interstage is shrunk so that its outer contour shape just fits within the stator envelope, and therefore such interstage is inserted along the envelope until it abuts the annular lip. Next, the interstage portion is allowed to warm under ambient temperature conditions, and as a result, the interstage portion undergoes thermal expansion and is tightly fitted in place. In a variation, the stator envelope may be heated to cause thermal expansion so that the interstage portion can be inserted and then cooled to produce an interference fit.

  An exemplary interstage transverse wall 26 for a claw pump is shown in FIG. The outer profile 84 of the interstage is shaped to match the inner profile 52 of the stator portion so that the interstage passes axially through the internal cavity 64 of the stator portion during assembly. Be able to. The interstage 26 has two bores 86, 88 that receive shafts 40, 42 (shown in FIG. 1). One of the bores 88 is configured to be an outlet from the upstream pumping chamber to the inlet of the downstream pumping chamber. The profile 84 in this example is such that the rotor generally rotates within the corresponding pumping chamber portion, and the left and right lobes of the illustrated interstage are each formed complementary to the corresponding pumping chamber portion. Suitable for example roots or claw pumping configurations. In another configuration example, the interstage is formed in two parts for attachment to the rotor and drive shaft, particularly when the rotor and interstage subassembly are assembled prior to insertion into the stator envelope. Also good.

  A modification of the embodiment of FIG. 1 is shown in FIGS. 9A and 9B. The same features in the two embodiments are given the same reference numerals, and the above viewpoint is omitted from the description of FIG.

  In FIG. 9, the method of fastening the interstage portion to the integral stator portion is different from the configuration example of FIG. Specifically, the integral stator component 90 has a plurality of through bores 94 aligned with the interstage portions 91, 92, 93. Fasteners 95 are configured to partially pass through each of the through bores and engage the interstage closure bore 96. The through bore 94 has a counterbore shoulder 97 for positioning the fastener in the radial direction. FIG. 9A shows six such fastening structures, and FIG. 9B is an enlarged view of one such structure, indicated by circle IXB in FIG. 9A.

  The pump shown in FIG. 9A may be assembled by first assembling the rotor and interstage subassemblies. Next, the subassembly may be inserted into the stator component 90. When in place, the subassembly is fastened in place by fastening each of the interstage portions 91, 92, 93 to the stator component 90 with fasteners 95. After fastening, the through bore 94 is preferably closed with a closure member 98 and sealed with a sealant. In this way, the rotor can be fixed relative to the shafts 40, 42 prior to insertion into the stator envelope 90, so that the angular alignment of multiple rotors can be accurately controlled. In another modification, the rotor may be manufactured integrally with the shaft. However, in this way, each of the interstages must be made of at least two components that can be assembled together between the rotors. Although it can be said that the modified configuration example is more likely to leak than the configuration example of FIG. 1, the modified configuration example has an advantage that the degree of rotor alignment is improved. Depending on the specific pumping requirements, accurate rotor alignment may be desirable even though leakage may increase.

  In the modified example of the configuration example of FIG. 9, the fixing means may be substantially the same as the fixing means described with reference to FIG. A fastener with an arcuate flange may be placed in the stator envelope, such fastener being accessible through a bore provided in the envelope for rotating the fastener with a tool, so that The fastener engages the interstage and locks it in place.

  According to the described embodiment, in a variant, the rotor and the interstage may be assembled in the stator. When the interstage part is positioned in the stator 20, the interstage part may be locked in place. This configuration means that the requirements for sealing are relaxed. This is because the pumped fluid is always maintained in the stator envelope. This arrangement not only requires the stator parts to be fastened together, typically by bolts, but also a known design in which a seal must be provided to prevent fluid from escaping from the pump between the stator parts. It can be said that it is in contrast. In the configuration of the present invention, such seals and fasteners are unnecessary, and thus the stator body can be made thin. This is because the stator body need not accept a seal or fastener. A thin stator is suitable for dissipating heat from the pumping chamber. Another cooling means, such as a jacket, may be placed near the heat increasing source. Because the heat can be easily dissipated, the thermal properties of the interstage are not so important, and as a result, the interstage material can be selected primarily to obtain other characteristics, such as erosion resistance. it can.

  The relaxation of the functional and mechanical requirements of the interstage means that the choice of constituent materials for the interstage is increased and unusual materials can be taken into account. The low amount of material also means that expensive materials such as nickel reinforced iron, stainless steel, PTFE, composites or ceramics can be considered.

  Since fewer parts are connected to each other in the axial order, there is less required axial tolerance at the interface, so the pump can be configured more accurately as a whole.

  The internal longitudinal cavity of the stator 20 can be made by machining relatively easily and accurately.

  Modifications to the above-described embodiments are possible while still falling within the scope of the invention as set forth in the claims. For example, the stator 20 is an integral component that constitutes each of the stator stages. However, certain advantages of the present invention are still obtained by employing, for example, two stator components, with each stator portion having an inner contour that constitutes two or more stator stages. Thus, again, there will be less axial interface between the stator components.

Claims (15)

  A multi-stage vacuum pump comprising a stator forming a plurality of pumping chambers and at least one shaft for rotatably supporting a plurality of rotors in corresponding pumping chambers, An integral stator envelope surrounding a plurality of axially adjacent pumping chambers provided around the shaft; and provided between the axially adjacent pumping chambers radially inward of the stator envelope. A multistage vacuum pump having at least one interstage lateral wall.   The multi-stage vacuum pump of claim 1, wherein an internal bore is formed extending axially through the stator envelope, the bore defining a profile of the respective pumping chamber.   A multi-stage vacuum pump according to claim 1 or 2, wherein the radial cross section of the internal bore at each pumping chamber is generally uniform in the axial direction.   The multistage vacuum pump according to claim 1 or 2, wherein the radial cross section of at least one pumping chamber is different from the radial cross section of at least one other pumping chamber.   The at least one end of the stator envelope is open to allow insertion of the at least one interstage lateral wall along the inner bore so as to be disposed between two pumping chambers. The multistage vacuum pump as described in any one of -4.   The multi-stage vacuum pump according to any one of claims 1 to 5, wherein the inner bore has a forming part for arranging an interstage wall between two pumping chambers.   The shaped portion has a stepped surface that extends radially inwardly into the inner bore and abuts when the lateral walls are accurately positioned between the pumping chambers. Multistage vacuum pump.   The multistage vacuum pump of claim 6, wherein the forming portion has at least one closure bore that receives a fastener for securing the lateral wall in place.   The multistage vacuum pump according to any one of claims 1 to 8, wherein the at least one interstage wall has a bore through which a fastener can be inserted in order to fix the interstage part to the stator envelope.   The multistage vacuum pump according to any one of claims 1 to 9, wherein the interstage portion is configured to be selectively fixable at two or more arrangement locations in the stator envelope.   11. One or more fasteners that fasten one or more of the interstage walls to the inner contour shape of the stator envelope. Multistage vacuum pump.   In the first state, the fastener can pass through the inner bore of the stator envelope in the first state, and in the second state, the fastener places the step part in place. The multistage vacuum pump of claim 11, wherein the multistage vacuum pump is configured to be fastened to a stator envelope.   13. At least one of the axially directed surface of the interstage wall or the axially directed surface of an adjacent rotor is coated with a lubricant. Multistage vacuum pump.   The interstage wall is not fixed at a predetermined location in the stator envelope, and the interstage wall is in a floating state between rotors. The multistage vacuum pump according to 1.   The stator comprised for the said multistage vacuum pump as described in any one of Claims 1-14.

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