JP2010540824A - Vacuum pump with two helical rotors - Google Patents

Abstract

A vacuum pump comprising an envelope (1), a mechanical drive element (19), and a pumping part (22). The pumping part (22) comprises two concave and convex helical rotors (A and B), each having a helical twist about the longitudinal axis. The rotors (A, B) are short and are extended and held downstream. The inlet passage (4) communicates with the inside of the envelope (1) by an inlet orifice (9). The outlet orifice (5) communicates with the inside of the envelope (1) by the outlet orifice (11). The inlet and outlet are axial with respect to the axis of the helical rotor (II, II-II).

Description

  The present invention relates to a pump device capable of generating and maintaining an appropriate vacuum in an apparatus.

  In an industrial semiconductor manufacturing process, the creation and maintenance of a vacuum in a device is common because several steps of manufacturing must be performed in a vacuum.

  During such manufacturing steps, the apparatus is connected to a pump device that reduces the internal pressure of the apparatus until a suitable vacuum is reached.

  In practice, known pump devices are generally in series in at least one first pump located at the discharge of the vacuum line and the flow path of the gas pumped between the first pump and the device. At least one second pump connected.

First known pump device is used in applications where it is necessary that the pressure in the apparatus is within a pressure range ranging from about ^10-2 mbar to about 10 mbar. In this case, a second pump that is a roots pump is generally used. This Roots pump is connected to the inlet of the first pump. This solution is generally used to rapidly pump large capacity devices or high process flows.

  Conventional roots pumps have two parallel rotors with bean-shaped cross sections that define interlocking lobes. The suction hole and the discharge hole are radially and perpendicular to the rotation axis of the rotor.

  However, the pump device constructed thereby is bulky, heavy and causes vibration and noise. To mitigate these drawbacks, companies move the pumping unit away from the device by the action of a conduit that can easily reach several meters in length. In order to maintain the desired pumping capacity, these conduits must be of high conductance. They are therefore broad and bulky and their internal volume is added to the volume of the device. As a result, the pumping system is less responsive because a large volume must be pumped to achieve the internal gas pressure within the device. Furthermore, it may be necessary to keep the gas at a high temperature in the vacuum line (especially a chemical process in which the gas is kept in a vaporized form by high temperatures up to 150 ° C.). Thereby, these pumping units require expensive heating devices to keep these large tubes hot.

  These drawbacks make it difficult to use these known pump devices in a clean room. The space in a clean room is very expensive and losing the very large space occupied by bulky devices and conduits is a major problem.

  A second pump of smaller size, such as a Roots pump, can be arranged, or a miniaturized conventional screw pump arrangement can be attempted directly at the suction portion of the vacuum line, ie the outlet of the device applied to the pump. This arrangement makes it possible to reduce the size of the conduit connecting the first pump and the second pump. This also significantly reduces the cost of heating the tube. However, radial inlet and outlet Roots pumps always generate vibration and noise. In addition, they are located at the outlet of the pumped device, which causes “backwash” contamination by feeding particles and powder back into the device.

  Furthermore, the Roots pump generally has the disadvantage that the shaft of the rotor is used in a horizontal position and the installation area becomes very large.

For applications requiring pressures below 10 ⁻² mbar, a molecular or turbomolecular second pump can be used. However, this type of pump cannot be used for applications where the gas needs to be heated in the pump device and / or for higher pressure applications.

  Companies are continually wanting to reduce the size and cost of equipment in their manufacturing room, especially in the semiconductor industry, where space in clean rooms is very expensive. The chemical industry is developing as well, and the pump device must always be more effective in terms of pump flow. These new size and flow criteria make it necessary to find new, less bulky and cheaper pump devices with clean and high pump flow rates.

EP-1,475,535

  The problem presented by the present invention can be used as a second pump, is small enough in size, has low enough noise output, and is not sufficiently contaminated to be placed in close proximity to the device without interfering with operation. Designing a vacuum pump with a high pump flow rate.

  The vacuum pump of the present invention must also be able to pump powders and other particles generated in the apparatus.

  According to another aspect, the present invention provides a more responsive pumping system for effectively creating and maintaining a vacuum in the apparatus.

  In addition to these objectives, to achieve other objectives, the present invention defines a cylindrical chamber with two envelopes that overlap in the transverse direction, the cylindrical peripheral surface and the end transverse surface. Each having a longitudinal axis defining a longitudinal direction and a transverse surface of an end defining a transverse direction, the inlet passage and the outlet passage traversing the envelope in two respective positions, these positions being generally Oppositely, the two rotors are each arranged to be rotatable in respective cylindrical chambers, the rotor having complementary lobe-shaped rotor bodies and rotor shafts that mesh, each lobe of each rotor having a respective cylindrical shape The rotor body has a radially spanned surface that cooperates in a sealed manner with the cylindrical peripheral surface of the chamber, and the rotor bodies each cross the end of the respective chamber. First and second transverse span surfaces cooperating in a sealed manner with the facing surface, each rotor body having a longitudinal axis between the first transverse span surface and the second transverse span surface. The inlet passage communicates with the inside of the envelope using an inlet orifice provided in the transverse surface of the first end and the outlet passage is essentially the second end. Communicating with the inside of the envelope using outlet orifices provided in the transverse surface of the section, each rotor overhanging by a rotor guide means located downstream of the rotor body in the flow direction of the pumped fluid The pump presents a vacuum pump equipped with rotor guide means upstream of the rotor body.

  According to the present invention, each of the two bodies of the rotor has a roots transverse profile and is a quarter turn between the first transverse span surface of the rotor and the second transverse span surface of the rotor. Designed with a helical twist, the inlet orifice is located along a first side of a plane defined by the rotor axis, and the outlet orifice is according to a second side of the plane defined by the rotor axis Be placed.

This quarter turn spiral twist provides the best compromise between rotor diameters. A pump flow rate of about 4000 m ³ / h can be achieved.

  Command and power means can also be provided to control the rotational speed of the rotor. The pump flow rate and upstream pressure can be easily adjusted according to the apparatus and processing steps.

  The single stage vacuum pump formed thereby has the advantage of a root pump or screw pump with a high pump flow rate. Its particular design gives the single-stage vacuum pump the advantage of having a large flow rate in a small volume with less vibration and noise generated and faster rotation options.

  By its design, pumped particles enter the pump axially by the inlet passage and cannot flow back into the device because the part moving upstream of the rotor bounces back, causing backflow in adjacent devices. It is also possible to avoid particle contamination. The design also avoids back-flow contamination due to the absence of bearings and lubrication products in the low pressure region downstream of the rotor.

  Therefore, this vacuum pump can be placed in the immediate vicinity of the device in which the vacuum is generated and maintained, and the function of the second pump can be accurately met.

  In addition, the absence of an element that mechanically guides the rotor downstream leaves a free flow area for selecting the shape and position of the pump's suction orifice, thereby ensuring the best pump flow in particular. .

  To ensure that the overhanging rotor has sufficient mechanical behavior and allows the rotor to rotate at high speeds without the risk of contacting the pump body, the overall height and diameter of the rotor body A relatively short rotor body with a ratio of less than 1 can be advantageously selected.

  Good results can be achieved by the ratio between the overall height and diameter of the rotor body being about 0.6.

  According to a first embodiment, the pump of the present invention comprises two rotor bodies, each having a load having a cross-section, the profile of the cross-section showing a profile that is conventional in a Roots pump .

This profile ensures the best compromise between the external form factor of the pump of the present invention and the flow rate of about 4000 m ³ / h intended to be obtained.

  For example, each rotor body can include two lobes.

  According to the second embodiment, each rotor body comprises at least three lobes. One advantage is better dynamic balance to reduce noise and vibration. Another advantage is that the compression ratio is better.

  On the other hand, one drawback is that the pump flow rate is reduced for the same form factor and the mechanical complexity is greater.

  According to an advantageous embodiment, the vacuum pump of the invention is kept in a position where the axis of the rotor is oriented along an orientation angle of less than 90 ° relative to the vertical direction. Means can be provided to ensure

  It should be noted that in known pump devices with a second roots pump having a radial inlet and outlet, particles present in the delivered gas tend to remain in the ineffective region. The particular design of the vacuum pump of the present invention, coupled with the non-horizontal orientation of the vacuum pump rotor shaft, prevents particle retention.

  Advantageously, the orientation angle can be selected to be less than 45 ° with respect to the vertical. Such an angle makes it possible to further reduce the installation area of the vacuum pump of the present invention and promote particle exclusion.

  Indeed, the specific design of the vacuum pump of the present invention allows it to be used along the vertical axis. Form factor is also minimal.

  Preferably, the vacuum pump of the present invention can comprise means for holding the inlet orifice at a higher position than the outlet orifice.

  This particular location of the inlet orifice relative to the outlet orifice further reduces the possibility of some degree of particle retention in the vacuum pump. The action of gravity actually increases the action of the gas flow that ejects the particles towards the outlet of the pump.

  According to one advantageous embodiment, the vacuum pump of the present invention is constructed from a material selected to withstand temperatures up to about 150 ° C.

  Thus, the choice of material allows the vacuum pump of the present invention to be used at the temperature normally required to vaporize a particular gas in the vacuum line. Such a temperature can also be achieved by careful selection of the material that forms the insulating part between the pumping and mechanical parts of the pump.

  According to one embodiment of the invention, the vacuum pump comprises a motor mounted on one of the drive shafts between the guide means.

  According to another embodiment, the vacuum pump comprises two synchronized motors, each mounted on a drive shaft between the guide means.

  According to another aspect, the present invention comprises a first pump having a first inlet and a first outlet and a second inlet connected to the outlet of the device by an inlet conduit, A second pump having a second outlet connected to the first inlet by a conduit of the second pump, the second pump being a single stage pump of the type defined above, The first pump, which is located in the immediate vicinity of the device, also presents a pumping system for creating and maintaining a vacuum in the device located remotely from the device.

  Preferably, the second inlet is arranged towards the outlet of the device, and the inlet conduit connects the second inlet directly to the outlet of the device. Thus, the inlet conduit can be very short or absent.

  Very advantageously, the single-stage vacuum pump designed according to the invention has the advantage that it can be placed in the immediate vicinity of the device. Thus, there are fewer conduits than prior art pump devices. Fewer conduits result in less space lost in the clean room, less pumping volume, and therefore higher responsiveness in the pump system.

  According to one advantageous embodiment, the pump system of the present invention comprises command and power means for controlling the speed of the second pump.

  The command and power means controls the second pump so as to adjust the speed of the second pump within a range of speeds that allows optimal control of the suction pressure by the discharge pressure.

  According to a first variant, the pump system further comprises a valve arranged at the discharge of the second pump, and command and power means for controlling the opening of the valve.

  According to a second variant, the pump system comprises a valve located at the discharge of the second pump, and the command and power means adjust the pressure in the device so that the speed of the second pump and / or Or it acts on the opening of the valve.

  Other objects, features and advantages of the present invention will become apparent from the following description of specific embodiments made with reference to the accompanying drawings.

FIG. 6 is a longitudinal cross-sectional view in the plane of the rotational axis of the pump according to one embodiment of the invention. 2 is a front view of the pump of FIG. 1 in a partial longitudinal section along the plane of the axis of rotation. FIG. It is a cross-sectional top view by CC plane of FIG. It is a top view of the pump of FIG. FIG. 3 is a perspective view of a set of transverse profile roots rotors according to one embodiment of the present invention. FIG. 6 is a front view of the set of rotors of FIG. 5. 1 is a schematic diagram of a pump system according to one embodiment of the present invention.

  Consider FIG. 1 illustrating a vacuum pump according to one embodiment of the present invention. This pump comprises a pump body in which two main parts are identified. The first main part comprises the mechanical drive element 19 of the pump according to the invention. The second main part comprises an envelope 1 that tightly seals the elements that make up the pumping part 22 of the pump.

  The first main portion includes a first drive shaft 21a and a second drive shaft 21b which are parallel to each other. The two drive shafts 21a and 21b are held by bearings 29a, 29b, 29c, and 29d. The rotor 30 of the motor is attached to the second drive shaft 21b between the bearings 29c and 29d, and rotates in the stator 31 of the motor fixed in the pump bodies 29c and 29d between the bearings. The electric conductor 20 supplies power for driving the second rotating drive shaft 21b to the stator 31 of the motor.

  The first drive shaft 21a defines a first axis II, and the second drive shaft 21b defines a second axis II-II.

  The drive gear 32 is fixed on the second drive shaft 21 b and meshes with the driven gear 33. The driven gear 33 is fixed to the first drive shaft 21a.

  The second main part comprises an envelope 1 which defines two parallel cylindrical chambers 2a and 2b, centered on axes II and II-II, which overlap in the transverse direction. These parallel cylindrical chambers 2a and 2b are defined by cylindrical peripheral surfaces 3a and 3b and end transverse surfaces 10 and 12.

  The inlet passage 4 is connected to a device in which a vacuum must be formed so as to allow fluid to enter the pump of the present invention.

  The inlet passage 4 basically communicates with the inside of the envelope 1 by an inlet orifice 9 provided in the transverse surface 10 at the first end.

  Two parallel rotors A and B are respectively arranged to be rotatable in respective cylindrical chambers 2a or 2b about respective axes II or II-II. Each rotor has a rotor body and a downstream coaxial shaft. The rotor bodies 6a and 6b are axially limited by the first coplanar transverse span surfaces 7a and 7b and by the second coplanar transverse span surfaces 8a and 8b. Each of the rotors A and B is attached so as to protrude at the end of the first drive shaft 21a or the second drive shaft 21b of the first main portion by a coaxial shaft 62a or 62b on the downstream side. Yes. Accordingly, the rotor is extended and held by the guide means (bearings 29a to 29d) arranged on the downstream side of the rotor body in the direction in which the pumped fluid flows. There is no guide means in the low gas pressure region upstream of the rotor bodies 6a and 6b.

  The guide means 29a-29d can be, for example, a smooth bearing, a magnetic bearing, or a gas bearing.

  An insulating wall 100 separates the first major part from the second major part. In this way, in order to prevent the pumped gas from depositing on the pumping element while maintaining a low temperature in the first main part equipped with the holding and driving means of the rotor, It is possible to heat the second main part containing the pumped gas.

  For example, a motor comprising a rotor 30 and a stator 31 can be mounted directly on the drive shaft 21a or 21b or between the two guide means 29a and 29b or 29c and 29d. This makes it possible to increase the compactness of the pump associated with the motor mounted on the end of the shaft after the gear.

  However, if the space between multiple pairs of guide means 29a and 29b or 29c and 29d is not sufficient, the solution just described allows the use of larger and more powerful motors if necessary. become.

  It can therefore be assumed that the vacuum pump according to the invention is operated by two synchronized motors, each mounted on a respective one of the drive shafts 21a or 21b between the guide means. This makes it possible to have more power within a given form factor.

  Consider FIG. 2 in which the same basic elements are numbered using the same reference numbers as in FIG.

  The outlet passage 5 traverses the envelope 1 and is arranged such that the inlet passage 4 and the outlet passage 5 traverse the envelope 1 in two generally opposite positions.

  The outlet passage 5 communicates with the inside of the envelope 1 basically by an outlet orifice 11 provided in the transverse surface 12 at the second end.

  In the pump of the present invention, it is easily observed that the fluid inlet and outlet pass axially.

  However, in this figure, it is observed that the inlet orifice 9 and outlet orifice 11 are moved relative to each other while remaining axially oriented. The inlet orifice 9 is blocked by the transverse plane and the outlet orifice 11 is in front of the transverse plane.

  FIG. 3 is a cross section taken along the plane CC of FIG. The same basic elements are indicated by the same reference numbers as in FIGS.

  This figure shows two rotors A and B. The rotor A comprises a rotor body 6a having two opposing lobes 60a and 61a. Rotor B includes a rotor body 6b having two opposing lobes 60b and 61b. The rotor bodies 6a and 6b are each arranged to be rotatable within the respective cylindrical chambers 2a and 2b. Each lobe 60a, 61a, 60b, 61b of each rotor body 6a and 6b has a cylindrical peripheral surface 3a and 3b of the respective cylindrical chamber 2a and 2b between a portion of the rotation path of the corresponding rotor A and B. With respective radial extent surfaces 25a or 26a and 25b or 26b, which cooperate in a sealed manner.

  The cross sections of the rotor bodies 6a and 6b have the same contour as that of the conventional roots profile.

  FIG. 4 is a top view of the pump of the present invention. The same basic elements are indicated by the same reference numbers as in FIGS. 5 and 6 show a plurality of pairs of rotor bodies 6a and 6b in perspective and top views, respectively.

  In these figures, each rotor body 6a and 6b has a respective longitudinal axis II or II-II between a first transverse scope surface 7a or 7b and a second transverse scope surface 8a or 8b. With a helical twist around the rotor, and the helical twist of the rotor is in the opposite direction.

  This helical twist of the roots rotor profile makes it possible to have wall suction and discharge orifices perpendicular to the axis and thus to have axial pumping.

  FIG. 4 also shows the movement in the entrance and exit passages.

  In the embodiment shown in FIGS. 1-7, each of the two rotor bodies is designed with a quarter turn helical twist between the first and second transverse scope surfaces. The inlet orifice 9 is arranged along the first side of the plane defined by the axes II and II-II of the rotor bodies 6a and 6b, and the outlet orifice is the axis II and of the rotor bodies 6a and 6b. Arranged along the second side of the plane defined by II-II.

  The rotor bodies 6a and 6b shown in these figures are relatively short and their axial height H is less than or equal to their overall diameter D.

  The H / D ratio is less than 1, preferably about 0.6.

  In the embodiment shown, the motor formed by the rotor 30 and the stator 31 is arranged on the second drive shaft between the bearings 29c and 29d, increasing the compactness of the pump.

  Next, the operation of the pump of the present invention will be described.

  The stator 31 is supplied with power via the conductor 20. This rotates the second drive shaft 21b, which drives the rotation of the first drive shaft 21a via gears 32 and 33. Then, the rotors A and B mechanically connected to the drive shafts 21a and 21b are completely rotated in opposite directions and driven.

  The pumped fluid continuously enters the pump of the present invention through the inlet orifice 9 and fills the volume between the rotor bodies 6a and 6b.

  The rotor bodies 6a and 6b always move the volume filled with fluid towards the outlet orifice 11 by their own rotation. During a portion of that movement, the fluid filled volume is separated from both the inlet orifice 9 and the outlet orifice 11. The volume filled with the fluid is then connected to the outlet orifice and the fluid is discharged. The pumping continues with the subsequent volume.

  The table below demonstrates some characteristics of the single stage vacuum pump of the present invention over conventional single stage Roots pumps. This table compares the performance of the pump (I) of the present invention relative to a conventional Roots pump (R) having the same rated flow in terms of speed, size, volume, weight, and power.

  With respect to the desired flow rate, it is confirmed that the pump of the present invention is less bulky, has a higher rotational speed, and consumes less power.

  The pump design of the present invention (high rotational speed, vertical position, lobe mounting principle, optimized lobe profile, material selection) reduces pump volume by 4 minutes compared to conventional roots pumps with the same flow rate The weight can be reduced to one third, and the power consumption can be reduced to about one half.

Furthermore, the pump of the present invention can operate effectively over a wide range of flow rates at low energy, for example by changing its rotational speed, from 1000 m ³ / h to over 4000 m ³ / h.

  In the embodiments shown in FIGS. 1, 2, 3, and 4, the rotor bodies 6a and 6b exhibit a quarter turn helical twist. However, without leaving the scope of the present invention, helical twists with different angle values can be selected and the rotor can be extended accordingly.

  The half-rotation twist forms a second intermediate fluid passage chamber and allows the second pump stage to be constructed. Thus, the resulting pump has two stages.

  FIG. 7 shows the pump system of the present invention. This system consists of device 13, where a suitable vacuum is desired.

  The outlet 13a of the device 13 is connected by an inlet conduit 16 to the second inlet 15a of the second pump 15b. The second pump 15 is of the type described above having two helical-twist rotors A and B (FIG. 1).

  The second pump 15 includes a discharge port 15 b connected to the suction port 14 a of the first pump 14 by an intermediate conduit 17. The outlet 14b of the first pump 14 allows the system of the present invention to discharge at atmospheric pressure.

  Advantageously, the second inlet 15a is arranged across from the outlet 13a of the device, and the inlet conduit 16 connects the second inlet 15a directly to the outlet of the device 13a. Accordingly, the suction conduit 16 is as short as possible and may not exist if the second pump 15 is connected directly to the device 13. Thus, an increase in the volume for pumping is avoided, as is the conductance loss due to the conduit. Thereby, the size of the second pump 15 is further reduced.

  On the other hand, the first pump 14 is connected to the second pump 15 by a relatively long intermediate conduit 17 and is moved away from the apparatus, such as outside the manufacturing chamber, limiting the form factor of the pump system in the manufacturing chamber. And avoid interfering with the device 13 by vibrations, noise, or other harmful phenomena.

Due to the action of the second pump operating from 10 ⁻³ mbar to 10 mbar, the gas transferred to the exhaust is at a pressure 10 to 100 times greater at the direct outlet of the processing chamber, thereby causing the processing gas to be The diameter of the conduit transferred to one pump is reduced, so that the cost of the connection can be reduced.

  Another result is that the particle trap is of a smaller size and can be placed downstream of the second pump instead of the chamber outlet, thereby preventing back flow of particles in the processing chamber. .

  Removing the intermediate conduit between the device 13 and the second pump 15 reduces the cost of the connection and saves power consumption.

  Maintenance and cleaning are also facilitated.

  The rotational speeds of the pump rotors A and B can be controlled by a command and power means 18 for supplying electric power to the motor (30 to 31, FIG. 1) of the second pump 15 of the present invention. Depending on the position of the second pump 15 in the immediate vicinity of the device 13, changes in the speed or pressure of the second pump 15 in its discharge immediately give the device a reaction.

  Thereby, it is possible to plan that the processing process carried out in the device 13 is controlled by the second pump 15.

  For example, the command and power means 18 can affect the speed of the second pump 15 to adjust the pressure in the device 13.

  One drawback is the inertia of the pump.

  As an alternative or supplement, a valve 40 arranged at the discharge of the second pump 15 is provided. The command and power means 18 controls the opening of the valve 40 that changes the discharge pressure. By changing the discharge pressure, the compression rate of the pump changes, and therefore the suction pressure, which is itself the pressure in the device 13, changes. Thereby, the command and power means 18 can control the opening of the valve 40 to adjust the pressure in the device 13, for example.

  The two systems may be a combined pump rotation speed and discharge valve. In that case, the command and power means 18 controls the second pump 15 to adjust its speed within the range of speeds that allow optimal control of the suction pressure by the discharge pressure, and the command and power means 18 The opening of the discharge valve 40 is controlled so that the suction pressure is controlled by the pressure. Document EP-1,475,535 teaches how to control and operate the second pump.

  In all situations, it is possible to exclude the regulating valve between the second pump and the device and exclude the turbulence and particle production valve in the device 13.

Claims (11)

A vacuum pump,
Two parallel cylindrical chambers are defined, the cylindrical chambers overlapping in a transverse direction and defined by a cylindrical peripheral surface and an end transverse surface, each axis defining a longitudinal direction, and a transverse direction An envelope having a transverse surface at the end of defining,
An inlet passage and an outlet passage intersecting the envelope at two respective positions,
The inlet passage communicates with the inside of the envelope using an inlet orifice provided in a transverse surface of the first end;
The outlet passage communicates with the inside of the envelope using an outlet orifice essentially provided in the transverse surface of the second end;
Entrance passage and exit passage,
Two rotors, each arranged to be rotatable within a respective cylindrical chamber, the rotors having complementary lobe-shaped rotor bodies and rotor shafts that mesh with each other,
Each lobe of each rotor has a radially spanned surface cooperating in a sealed manner with the cylindrical peripheral surface of the respective cylindrical chamber, the rotor body being each at the end of the respective chamber. Having first and second transverse span surfaces cooperating in a sealed manner with the transverse surface;
Each rotor body has a helical twist about a longitudinal axis between the first transverse span surface and the second transverse span surface;
Each rotor is extended and held by a rotor guide means arranged on the downstream side of the rotor body in the flow direction of the pumped fluid, and the pump is equipped with rotor guide means on the upstream side of the rotor body. Two rotors,
Each of the two bodies of the rotor has a roots transverse profile and is a quarter turn spiral between the first transverse span surface of the rotor and the second transverse span surface of the rotor. Designed with a twist, the inlet orifice is disposed along a first side of a plane defined by the axis of the rotor, and the outlet orifice is a second side of the plane defined by the axis of the rotor Arranged according to the vacuum pump.   2. A vacuum pump according to claim 1, wherein the ratio between the overall height and diameter of the rotor body is less than one.   The vacuum pump according to claim 1, wherein each rotor body includes two lobes.   The vacuum pump according to any one of claims 1 to 3, wherein each rotor body includes at least three lobes.   5. A vacuum pump according to any one of claims 1 to 4, wherein each rotor shaft comprises a coaxial shaft of a respective downstream fixed rotor at the end of a respective drive shaft. Vacuum pump.   6. A vacuum pump according to any one of claims 1 to 5, comprising a motor mounted on one of the drive shafts between guide means.   6. A vacuum pump according to any one of the preceding claims, comprising two synchronized motors each mounted on a respective drive shaft between the guide means. A pump system for creating and maintaining a vacuum in the apparatus,
A first pump having a first inlet and a first outlet; and a second inlet connected to the outlet of the device by an inlet conduit and connected to the first inlet by an intermediate conduit A second pump having a second outlet formed,
The second pump is a single stage pump of the type defined in one of the claims 1 to 7,
The second pump is disposed in the immediate vicinity of the device;
The pump system wherein the first pump is held away from the device.   10. A pump system according to claim 9, wherein the second inlet is disposed across the device outlet, and the inlet conduit connects the second inlet directly to the outlet of the device. system.   11. A pump system according to any one of claims 9 to 10, wherein the second pump is adapted to adjust its speed within a range of speeds allowing optimal control of the suction pressure by means of the discharge pressure. A pump system comprising a command and power means for controlling the motor.   12. The pump system according to any one of claims 9 to 11, comprising a valve arranged at a discharge part of the second pump, wherein the command and power means adjust the pressure in the apparatus. A pump system acting on the second pump speed and / or valve opening.

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