EP3112688B2 - Split flow vacuum pump and vacuum system with a split flow vacuum pump - Google Patents

Description

The invention relates to a vacuum pump of the split-flow pump type.

So-called split-flow vacuum pumps are used in practice to evacuate several chambers, for example of a mass spectrometer system, at the same time. The split flow vacuum pumps make it possible to dispense with a pump system consisting of several individual pumps and to evacuate several chambers with a single pump.
Split flow vacuum pumps have the advantage that they only require a small amount of space for the vacuum system. The split-flow vacuum pumps are not only used in analysis devices, but also, for example, in leak detectors whose analysis principle is also based on mass spectrometry.

State of the art ( DE 43 31 589 A1 ) A turbomolecular pump is known which has a plurality of suction connections, each of which is connected to one of the vacuum chambers of a device, for example a mass spectrometer. The suction ports supply gas to various axially spaced locations of the rotor. Several so-called rotor-stator packages are arranged along the rotor axis, each of which compresses gas. A high vacuum side stator pack creates a pressure ratio between its inlet and outlet. The inlet is connected to a first vacuum chamber. The outlet is connected to the inlet of the next rotor-stator package. In addition, this area between two rotor-stator packages is connected to a second vacuum chamber. Due to the pressure ratio created by the first rotor-stator package and the poor conductance between the vacuum chambers, the pressure in the two vacuum chambers is different. With a corresponding number of rotor-stator packages, several vacuum chambers can be evacuated to different pressures, with each suction port being assigned a rotor-stator package. It turns out that rotors that are very long compared to their diameter are difficult to handle, since the rotors are operated at speeds in the range of a few 10,000 revolutions per minute.

Another variant for evacuating an arrangement with several vacuum pumps is to provide each vacuum pump with its own flange. A vacuum pump suitable for the pressure range is then connected to this. This route is unpopular due to the high cost of the large number of vacuum pumps. There is also a need for compact devices. However, these cannot be realized with a large number of vacuum pumps.

In a large number of applications, several vacuum chambers are arranged in series and connected to one another by bores with a low conductivity. From one end of the series to the other, the gas pressure inside the vacuum chamber decreases. The holes are designed in such a way that a particle beam can pass through them and thus through the row of vacuum chambers. The lowest pressure vacuum chamber often contains an analysis device, such as a mass spectrometer.

Split flow vacuum pumps are known from practice which have three or four radial inlets and which have at least four pump stages. Pump stages are usually turbomolecular pump stages. These are often combined with other pump stages, for example Holweck pump stages or Gaede pump stages.

In the applications, it is necessary to provide more and more taps for split-flow vacuum pumps with high pumping speeds. This means that the number of rotor disk packs has to be increased, which in turn leads to manufacturing difficulties if, for example, the rotor disks are only stacked on the rotor from one side.

By forming variants with regard to the inner diameter of the rotor disks (shaft joint diameter), several disk packs with several axial stops on the shaft can be implemented. However, this means that there must be many different disks in the assembly of the pumps. This large number of different discs are also expensive to manufacture.

On the state of the art ( DE 10 2009 035 332 A1 and EP 2 789 889 A1 ) belong to vacuum pumps that have multiple turbomolecular pumping stages. Inlets are provided between the turbomolecular pumping stages to evacuate different chambers of a chamber system. In these prior art vacuum pumps, the inlets are located between or before each pumping stage. These vacuum pumps, which are part of the prior art, can be further improved in terms of their pump performance and their possible uses.

Furthermore belong to the state of the art ( EP 2 378 129 A2 and EP 1 807 627 B1 ) Vacuum pumps in which inlets are also provided before and between pump stages, which are designed as Hohlweck pump stages or turbomolecular pump stages. These pumps can also be further improved with regard to their possible uses.

The technical problem on which the invention is based is to provide a split flow vacuum pump in which the number of inlets is increased without increasing the number of pump stages provided.

This technical problem is solved by a split-flow vacuum pump having the features according to claim 1.

The split-flow vacuum pump according to the invention with at least three radial inlets and with at least four pump stages, with at least two pump stages being designed as turbomolecular pump stages, is characterized in that the at least three inlets are designed as main inlets, which are arranged in the axial direction between the turbomolecular pumping stages, with at least one additional radial secondary inlet being provided, which is arranged in the area of at least one turbomolecular pumping stage and that the at least one secondary inlet is located between two Stator disks or between two rotor disks or between a stator disk and a rotor disk is arranged at least one turbomolecular pumping stage.

The design of the vacuum pump according to the invention makes it possible to provide at least one secondary inlet in addition to the main inlets. The main inlets are located between the pumping stages as known in the art. What is new about the invention is that at least one additional inlet is provided, which is arranged in the area of at least one turbomolecular pump stage. This means that what is known as a tap, that is to say the inlet, is not arranged between the turbomolecular pumping stages, but that the tapping leads radially into a disk pack of the at least one turbomolecular pumping stage.

As a result, significantly more taps are achieved, ie inlets with a single pump over a certain axial length. The invention makes it possible to evacuate as many chambers as possible in a multi-chamber system over a short axial length.

The rotor can be designed in one piece or in several pieces.

According to an advantageous embodiment of the invention, the at least one auxiliary inlet has a central axis and the central axis is arranged between a first and a last disk of the at least one turbomolecular pumping stage.

This means that the secondary inlet leads between the disks of the disk pack of the at least one turbomolecular pump stage. This creates additional inlets in addition to the prior art inlets located between the pumping stages, so that a larger number of vacuum chambers can be evacuated.

According to the invention it is provided that the at least one secondary inlet is arranged between two stator disks or between two rotor disks or between a stator disk and a rotor disk of at least one turbomolecular pump stage. According to a further advantageous embodiment of the invention, it is provided that the secondary inlet is arranged between the disks of a stator core, while a main inlet is arranged between the stator cores.

If several secondary inlets are provided, these can also be arranged radially offset from one another at the same axial height of the rotor. In this case, the secondary inlets are arranged in a disk pack between two rotor disks and distributed radially around the circumference. However, they can also lie on one level.

According to the invention, the at least one auxiliary inlet is arranged between two adjacent stator disks or between adjacent rotor disks or between a stator disk and an adjacent rotor disk of at least one turbomolecular pumping stage. This means that the secondary inlets are chosen to be relatively small in terms of their diameter and are arranged between the discs.

It is advantageously provided that a pumping speed of the at least one secondary inlet is lower than the pumping speed of a main inlet.

The secondary inlets serve to increase the number of taps in a multi-chamber system to be evacuated.

There is a relatively large amount of space between the individual pump stages, ie between the individual disk packs or other pump stages, for example Gaede or Holweck pump stages, so that the main inlets can have a relatively large cross section. The secondary inlets lead between disks of the turbomolecular pump stages and for this reason only have a relatively small cross-section.

According to a further advantageous embodiment of the invention, it is provided that with n disks n−1 secondary inlets are provided.

This means that the number of sub-intakes is less than the number of discs. If a disk pack of the turbomolecular pump stage is formed from two disks, a secondary inlet can be provided between these two disks.

However, it is also possible to provide several radial side inlets in the area of a turbomolecular pump stage. Equally, it is also possible to provide one or more secondary inlets in each of these turbomolecular pumping stages when there are several turbomolecular pumping stages. Various turbomolecular pumping stages can be designed with and without side inlets.

It is advantageously provided that in addition to the at least one turbomolecular pump stage, at least one Holweck pump stage and/or a Siegbahn pump stage and/or a Gaede pump stage and/or a side channel pump stage and/or a screw pump stage is provided.

Split flow pumps usually consist of one or more turbomolecular pump stages and at least one other pump stage.

By combining different pump stages, the pressure conditions in the chambers to be evacuated can be adjusted accordingly.

For example, it is possible to provide a main inlet between the pump stages, for example between two turbomolecular pump stages, and to additionally arrange a Holweck pump stage, for example. According to the invention, at least one further secondary inlet is additionally arranged in the area of the at least two turbomolecular pump stages.

According to a further advantageous embodiment of the invention, it is provided that a turbomolecular pumping stage is formed from one or more rotor disks and from one or more stator disks.

A pump stage usually consists of at least one stator disk and at least one rotor disk. A plurality of stator disks and a plurality of rotor disks, which mesh alternately, are often provided. According to the invention, it is advantageously provided that with n panes, n−1 secondary inlets are provided. For example, if there is a stator disc and a rotor disc forming a turbomolecular pumping stage, the inlet is located between these discs.

A further advantageous embodiment of the invention provides that a stator disk and an adjacent rotor disk of a turbomolecular pumping stage define an axial length L, and that a distance between two turbomolecular pumping stages is at least as large as this length L.

This stipulates that at least one stator disk and one rotor disk form at least one turbomolecular pumping stage. If the distance between adjacent stator disks and/or adjacent rotor disks is so great that the length L is exceeded, a new turbomolecular pumping stage begins according to the invention. An inlet in this area between the turbomolecular pumping stages is considered the main inlet. An inlet in the area of the turbomolecular pumping stage itself is considered a side inlet.

The embodiment according to the invention with regard to the inlets can in principle also be used in a turbomolecular pump.

A pump stage advantageously consists of at least one rotor disk and at least one stator disk. In this case, the auxiliary inlet is located between the rotor disk and the stator disk.

According to a further advantageous embodiment of the invention, a vacuum system is provided with at least one vacuum pump and at least one recipient, in which a detachable connection is provided between the vacuum pump and the recipient, with at least one elastomer seal for sealing the connection towards the atmosphere side and at least one elastomer seal towards the vacuum side a gap seal is provided, which is characterized in that at least one suction channel and/or at least one suction opening is/are provided between the elastomer seal and the gap seal.

This embodiment has the advantage that an elastomer seal is used at the sealing points on the atmosphere side. This is advantageously designed as an O-ring. At least one gap seal is used as the second sealing element between the elastomer seal and the ultra-high vacuum connection, for example. The surfaces of the recipient (chamber) and a surface of the pump housing are pressed against each other.

Fig. 1

einen Längsschnitt durch eine Anordnung mit einer nicht zur Erfindung gehörenden Vakuumpumpe;

Fig. 2

eine schematische Darstellung eines Rotors mit Scheibenpaketen mit Haupt- und Nebeneinlässen einer nicht zur Erfindung gehörenden Vakuumpumpe;

Fig. 3

eine Splitflow-Vakuumpumpe im Längsschnitt;

Fig. 4

eine Prinzipskizze eines Rotors mit auf dem Rotor angeordneten Rotorscheiben;

Fig. 5

eine Prinzipskizze eines Rotors einer Splitflow-Vakuumpumpe gemäß dem Stand der Technik;

Fig. 6

ein geändertes Ausführungsbeispiel;

Fig. 7

eine Vakuumpumpe in perspektivischer Ansicht mit Vakuumanschluss.

Fig. 8

ein geändertes Ausführungsbeispiel eines Rotors mit zwei Nebeneinlässen;

Fig. 9

ein geändertes Ausführungsbeispiel einer Pumpe mit zwei Nebeneinlässen;

Fig. 10

ein geändertes Ausführungsbeispiel mit Rotorscheiben mit Bund.

Further features and advantages of the invention result from the associated drawing, in which several exemplary embodiments of a vacuum pump according to the invention are shown only by way of example. Show in the drawing:

1

a longitudinal section through an arrangement with a vacuum pump not belonging to the invention;

2

a schematic representation of a rotor with disk packs with main and secondary inlets of a vacuum pump not belonging to the invention;

3

a longitudinal section of a split-flow vacuum pump;

4

a schematic diagram of a rotor with rotor disks arranged on the rotor;

figure 5

a schematic diagram of a rotor of a split flow vacuum pump according to the prior art;

6

a modified embodiment;

7

a perspective view of a vacuum pump with a vacuum connection.

8

a modified embodiment of a rotor with two side inlets;

9

a modified embodiment of a pump with two auxiliary inlets;

10

a modified embodiment with rotor disks with collar.

1 shows a vacuum pump 1, which is designed as a so-called split-flow vacuum pump. The vacuum pump 1 is connected to a multi-chamber vacuum system 2 . The multi-vacuum system 2 has four chambers 3, 4, 5, 6, which are to be evacuated by the vacuum pump 1. The gas pressure in the chambers 3, 4, 5, 6 increases in this order. The chambers 3, 4, 5, 6 are separated from one another by partitions 7, 8, 9, with bores 9, 10, 11 establishing a connection. These holes 9, 10, 11 are, for example arranged and dimensioned in such a way that a particle beam can pass through all chambers 3, 4, 5, 6. In particular, the first partition wall 7 separates the first chamber 3 and the second chamber 4 from each other, while the second partition wall 8 separates the second chamber 4 from the third chamber 5 and the third partition wall 9 separates the third chamber 5 from the fourth chamber 6. The dashed arrows in the 1 illustrate the gas flow.

The vacuum pump 1 has a shaft 13 which carries rotor disks 14-19. The rotor disks 14 to 19 are in engagement with the stator disks 20. The rotor disks 14, 15, 16 form a first disk pack 21 and the rotor disks 17 to 19 form a second disk pack 22. The disk pack 22 forms with the stators 20 a high-vacuum side rotor-stator pack. The disk pack 21 forms, together with the stator disks 20, a rotor-stator pack on the intermediate vacuum side. As is known in the prior art, the blades in both sets are fastened to support rings on both the stator and rotor side or are formed in one piece with the latter. A first gas inlet 23 is located in front of the rotor-stator core on the high-vacuum side, and a second gas inlet 24 is located in front of the rotor-stator core on the pre-vacuum side.

A first main inlet 23 leads from the multi-chamber vacuum system into the vacuum pump 1. From the second chamber 4, a second main inlet 24 leads into the vacuum pump 1. From the vacuum chamber 5, another main inlet 25 leads into the vacuum pump 1 and from the vacuum chamber 6, another main inlet leads 26 into the vacuum pump 1.

The main inlets 23,24,25,26 are located between the turbomolecular pumping stages 21,22.

A first secondary inlet 27 is arranged in the area of the turbomolecular pump stage 22 and leads from the vacuum chamber 5 into the vacuum pump 1 . In addition, another secondary inlet 28 leads from the vacuum chamber 6 in the area of the turbomolecular pump stage 21 into the vacuum pump 1.

Thus, the number of inlets through the sub-inlets 27, 28 is increased. The secondary inlets 27, 28 are arranged in the region of the turbomolecular pump stages 21, 22.

The rotor shaft 13 has areas with different diameters.

A first area 29 is an area with the largest diameter. On both sides of the shaft 13 are two areas 30, 31 with smaller diameters. This in turn is followed by areas 32, 33 with an even smaller diameter of the shaft 13. No rotor disks are arranged in the region 29 of the largest diameter of the shaft 13 . The rotor disk 16 is arranged in the area 30 and is locally clearly defined by a stop 34 formed by the stepped shoulder between the area 29 and the area 30 .

The same applies to the rotor disk 15, which is fixed by a stop 35 between the areas 30, 32.

This also applies to the rotor disk 17, which is fixed on the shaft 13 by a stop 36, and the rotor disk 18, which is fixed on the shaft 13 by a stop 37. Between the rotor disks 14, 15 and the rotor disks 18, 19 a spacer sleeve 38 is arranged in each case. The rotor discs 14 to 19 are placed exactly on the shaft 13 by the stops 34 to 37 so that narrow gaps can be formed between the rotor discs 14 to 19 and the stator discs 20 .

A further advantage of the invention lies in the fact that the rotor disks 14 to 19 are placed exactly on the shaft, as a result of which very small gaps can be formed. This increases the pumping capacity of the vacuum pump 1. The use of many identical parts means that the pump is inexpensive to manufacture. In the present exemplary embodiment, two sets of rotor disks, each with the same inner diameter, are arranged on both sides of the region 29 of the shaft 13 with the largest diameter.

Another advantageous embodiment of the invention is an embodiment in which 29 grooves 39, 40 are arranged in the region of the largest diameter, which reduce the mass of the shaft. Since the split flow vacuum pumps have a very long overall length, the modal behavior of the rotor and in particular the rotor shaft is critical. For this reason, according to the invention, the mass and thus also the weight of the shaft are reduced while the rigidity remains the same.

The vacuum pump 1 has a housing 41 . The housing 41 has a constriction 42 in order to reduce thermal transitions between the high-vacuum side and the pre-vacuum side in the housing 41 . This constriction reduces the thermal conductivity. It is possible to additionally provide a reinforcement, not shown, in the area of the constriction 42 . The housing can also be divided in the area of the constriction 42 and a thermal seal can be arranged between the two parts of the housing.

The shaft 13 is mounted on one side by means of a magnetic bearing 43 . Counter bearings 43b are arranged in a holder 43a, which is only shown schematically. On the other hand, the bearing is not shown. The bearing on the side that is not shown can be, for example, an oil-lubricated ball bearing.

In 1 only turbomolecular pump stages 21, 22 are shown.

There is also the possibility of providing a Holweck pump stage and/or a Siegbahn pump stage and/or a Gaede pump stage and/or a side channel pump stage and/or a threaded pump stage in addition to the turbomolecular pump stages.

The rotor disk 15 and the stator disk 20 have an axial length L when viewed in the axial direction on. The distance between the turbomolecular pumping stages 21, 22 is greater than the length L.

2 shows the shaft 13 with rotor disk packs 44, 45, 46, which form turbomolecular pump stages 44, 45, 46 with stator disc packs (not shown). The gas flow is represented by an arrow 47 .

Arrows 48 represent the gas flow fed from two main inlets 24,25 to the turbomolecular pumping stages 45,46. The arrows 49 indicate the gas flow which is supplied to the pumping system from two side inlets 27, 28 in the region of the turbomolecular pumping stages 44, 45.

The secondary inlets 27, 28 are arranged in the region of the turbomolecular pumping stages 44, 45, while the main inlets 24, 25 have their supply between the turbomolecular pumping stages 44, 45 and 46.

3 shows vacuum pump 1, which once again makes it clear that it has turbomolecular pump stages 44, 45, 46, 49. The turbomolecular pumping stages 44, 45, 46, 49 consist of rotor disks and stator disks which are arranged in an intermeshing manner. In addition, main inlets 23, 24, 25, 26 are provided, which are arranged in front of the pumping stage 44 or between the pumping stages 44, 45, 46, 49.

The shaft 13 is supported by a magnetic bearing 43 and a ball bearing 50 . The ball bearing 50 is an oil-lubricated ball bearing. The shaft 13 is driven by a motor 51.

A secondary inlet 27 is provided in the area of the turbomolecular pump stage 44 . A secondary inlet 28 is provided in the area of the turbomolecular pumping stage 45 and a secondary inlet 52 is provided in the area of the turbomolecular pumping stage 46 .

This embodiment increases the number of inlets from the four main inlets 23, 24, 25, 26 to a total of seven inlets, namely plus the three secondary inlets 27, 28, 52.

4 shows a partial section through the shaft 13. The shaft 13 has the 1 shown areas 29 with the largest diameter, the adjoining areas 30, 31 with a smaller diameter and the in turn adjoining areas 32, 33 with a further reduced diameter. In the areas 30, 31, the rotor disks 16, 17 are arranged. In the areas 32, 33, the rotor disks 15, 18, 19 are arranged. The rotor disks 15, 18, 19 have the same inner diameter. The rotor disks 16, 17 also have the same inner diameter. This makes it possible to construct an inexpensive pump using a large number of identical parts.

The difference in diameter between the areas 29, 30 forms the stop 34. Between the areas 29, 31 the stop 36 is provided. The stop 35 is arranged between the areas 30, 32 and the stop 37 is provided between the areas 31, 33.

The assembly direction of the discs 15, 16 is indicated by the arrow A. The assembly direction of the rotor disks 17, 18, 19 is indicated by the arrow B. A central axis of the shaft 13 is marked with M. FIG. The shaft 13 and the rotor disks 15, 16, 17, 18, 19 are rotationally symmetrical about the central axis M.

figure 5 shows a shaft 13 with two turbomolecular pump stages 21, 22, which are arranged in a housing 41 of a split-flow pump. The housing 41 has an inlet 24 .

This prior art embodiment shows that a customer housing 60 has an inlet 61 that is radially offset from the inlet 24 . The axial length of the pump and the customer chamber 60 do not match.

According to 6 a solution is shown how the highest possible conductance can still be achieved. For this purpose, the housing 41 has a web 62 in the area of the inlet 24 . The design of the web, to which the stator disks (not shown) can be attached, results in a larger cross section in the area of the inlet 24 and thus a higher conductance.

7 1 shows a vacuum pump 1 with vacuum connections 72, 73, 75. The vacuum connection 72 has an elastomer seal 76 and a gap seal 77. Between the elastomer seal 76 and the gap seal 77 there is a suction channel 78 in which intermediate suction devices 79 are arranged. A suction opening 80 is arranged in the vacuum connection 75 . The intermediate suctions 79 lead into a through-bore 81, which leads to the intermediate stage 73. A connecting channel 82 is provided for a sealing arrangement of the vacuum connection 75 , so that the vacuum connection 75 is also evacuated via the suction opening 80 via the through-hole 82 .

8 12 shows a rotor 126, which is shown only schematically, with rotor disks 14, 15, 16, 17. Between the rotor disks 16, 17, two secondary inlets 27, 28 are arranged. The secondary inlets 27, 28 are radially spaced from each other and both lead between the rotor discs 16, 17.

9 shows a housing 60 of a vacuum pump with the vacuum connections 72, 73. Two secondary inlets 27, 28 are provided, which are arranged in one plane.

10 shows the rotor shaft 126 on which the rotor disks 14, 15 are arranged. Between the rotor disks 14, 15, a stator disk 20 is arranged schematically. The rotor disks 14, 15 each have a collar 127. The collar 127 replaces the spacer sleeve 38, which is 1 is shown.

reference numbers

1

vacuum pump

2

Multi-chamber vacuum pump system

3

chamber

4

chamber

5

chamber

6

chamber

7

partitions

8th

partitions

9

partitions

10

drilling

11

drilling

12

drilling

13

Wave

14

rotor discs

15

rotor discs

16

rotor discs

17

rotor discs

18

rotor discs

19

rotor discs

20

stator discs

21

Turbomolecular pump stage with disc pack

22

Turbomolecular pump stage with disc pack

23

main entrance

24

main entrance

25

main entrance

26

main entrance

27

side entrance

28

side entrance

29

Area of the shaft 13 with the largest diameter

30

Area of the shaft 13 with a smaller diameter

31

Area of the shaft 13 with a smaller diameter

32

Area of the shaft 13 with the smallest diameter

33

Area of the shaft 13 with the smallest diameter

34

attack

35

attack

36

attack

37

attack

38

sleeve

39

groove

40

groove

41

Housing

42

constriction

43

magnetic bearing

43a

bracket

43b

counter bearing

44

Turbomolecular pump stage with rotor disk packs

45

Turbomolecular pump stage with rotor disk packs

46

Turbomolecular pump stage with rotor disk packs

47

arrow gas flow

48

arrow gas flow

49

turbomolecular pumping stage

50

ball-bearing

51

engine

52

side entrance

53

groove

54

groove

55

drilling

56

intersection

57

groove

58

groove

59

sleeve

60

Housing

61

inlet

62

web

72

vacuum connections

73

vacuum connections

75

vacuum connections

76

elastomer seal

77

gap seal

78

suction channel

79

intermediate suction

80

suction port

81

through hole

82

connection

126

rotor

127

Federation

A

Arrow

B

Arrow

L

axial length

M

central axis

Claims (8)

1. A split flow vacuum pump (1) with at least three radial inlets (24, 25, 26) and with at least four pump stages (21,22,44,45,46), wherein at least two pump stages are formed as turbomolecular pump stages (44, 45, 46),

   - characterised in that the at least three inlets (24,25,26) are formed as main inlets, which are arranged in axial direction between the turbomolecular pump stages (44, 45, 46),

   - wherein there is provided in addition at least one radial auxiliary inlet (27, 28, 52), which is arranged in the region of at least one turbomolecular pump stage (44, 45, 46)

   - and in that the at least one auxiliary inlet (27, 28,52) is arranged between two stator discs (20) or

   - between two rotor discs (14 to 19) or

   - between a stator disc (20) and a rotor disc (14 to 19) of at least one turbomolecular pump stage (1).
2. A split flow vacuum pump according to claim 1, characterised in that the at least one auxiliary inlet (27, 28, 52) has a central axis and in that the central axis is arranged between a first and a last disc (14 to 19; 20) of the at least one turbomolecular pump stage (21, 22, 44, 45, 46).
3. A split flow vacuum pump according to claim 1 or 2, characterised in that at least two auxiliary inputs (124, 125) are arranged radially of offset to each other.
4. A split flow vacuum pump according to claim 1, characterised in that the at least one auxiliary inlet (52) is arranged between two adjacent stator discs (20) and/or between two adjacent rotor discs (14 to 19) and/or between a stator disc (20) and an adjacent rotor disc (14 to 19) of at least one turbomolecular pump stage (1).
5. A split flow vacuum pump according to any one of the preceding claims , characterised in that a suction capacity of the at least one auxiliary inlet (27, 28, 52) is smaller than the suction capacity of a main inlet (23, 24, 25, 26).
6. A split flow vacuum pump according to any one of the preceding claims, characterised in that with n discs (14 to 19, 20) there are provide n-1 auxiliary inlets (27, 28, 52).
7. A split flow vacuum pump according to any one of the preceding claims, characterised in that a stator disc (20) and an adjacent rotor disc (14 to 19) of a turbomolecular pump stage (21, 22, 44, 45, 46) determines an axial length (L), and in that a spacing between two turbomolecular pump stages (21, 22, 44, 45, 46) is at least as large as the length (L).
8. A vacuum system with at least one split flow vacuum pump according to any one of the preceding claims , and at least one container in which between the vacuum pump and the container there is provided a releasable connection, wherein there are provided for sealing the connection with respect to the atmospheric side at least one elastomeric seal (76) and in the direction of the vacuum side at least one gap seal (77), characterised in that between the elastomeric seal (76) and the gap seal (77) at least one suction channel and/or at least one suction opening (80) is/are provided.

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