EP3851680B1 - Molecular vacuum pump and method for influencing the suction performance of same - Google Patents

Description

The present invention relates to a molecular vacuum pump, a method for influencing the pumping speed of a molecular vacuum pump, a leak detector with a molecular vacuum pump and the use of a molecular vacuum pump for searching for a leak in a vacuum system.

In various vacuum applications, special requirements are placed on the vacuum performance of a molecular vacuum pump, especially with regard to pumping speed. A method known from the prior art and a molecular vacuum pump are in the DE4228313 A1 disclosed.

It is an object of the invention to influence the pumping speed of a molecular vacuum pump in a simple and targeted manner at a specific point in the flow path of the molecular vacuum pump.

This task is solved by a method according to claim 1. This serves to influence the pumping speed, in particular an internal pumping speed, of a molecular vacuum pump, which comprises at least one molecular pumping stage, by means of which a gaseous medium can be conveyed along a flow path from an inlet to an outlet of the molecular vacuum pump, the pumping stage having a pumping direction and transverse to the pumping direction has a passage cross section. The pumping speed is influenced at a first point in the flow path of the molecular vacuum pump, namely by providing a blocking element at a second point in the flow path of the molecular vacuum pump, different from the first point, through which the passage cross section is locally reduced.

An idea underlying the invention is a targeted weakening of the suction speed at the second point in order to specifically influence the suction speed at another point, namely the first point. The provision of the blocking element allows the suction speed at the second point to be specifically influenced. As such, a blocking element has a particularly simple structure and can be produced inexpensively, so that the targeted influence on the suction speed at the second point can be achieved using particularly simple means. It goes without saying that the suction speed at the second point is not completely arbitrary due to the blocking element at the first point, i.e. H. is not infinitely adjustable. Rather, the pumping speed at the second point is typically limited by various circumstances, in particular the other structure of the molecular vacuum pump. In principle, it can also be the case that the suction speed at the second point can only be reduced by the blocking element at the first point. Even though a generally high suction speed is often desired in many vacuum applications, reducing the suction speed at the second point may also be necessary or advantageous in special vacuum applications. Ultimately, the method according to the invention can also increase the backflow of the gaseous medium as a whole or for individual gas components.

By locally reducing the passage cross section, the blocking element causes in particular a local reduction in the conductance at the second point.

In particular, it proves to be advantageous if the blocking element is a static element and/or is arranged on a stator of the pump, since changing the design of the rotor would generally be significantly more complex, particularly due to dynamic forces on the rotor. The invention can therefore be implemented by modifying an existing pump without changing its rotor to have to. In principle, a blocking element can also be arranged on the rotor, for example.

The first place where the pumping speed should be influenced can, for example, be an inlet area of the molecular vacuum pump. Preferably, however, the first point can be different from an inlet region of a first or only inlet of the molecular vacuum pump in the pumping direction. In other words, the first point is in particular not at a so-called high vacuum inlet. However, the first point can preferably be arranged, for example, at an intermediate inlet. Alternatively, the first point can also be provided outside of all inlet areas, for example.

According to the invention, the first point can be located within a housing of the molecular vacuum pump and/or within an envelope of pump-active elements. A suction speed that is effective there is referred to as the internal suction speed. In connection with the previous paragraph, the first point can in particular be provided in an area which is arranged within the housing and is directly connected to an inlet - that is, without an intermediate pump-active element. You can also talk about the internal suction speed at the inlet, which should be influenced. This applies in particular to an intermediate entry. In the case of a turbomolecular pump stage or a Holweck pump stage, the first point can, according to the invention, be provided in an axial region of an inlet or intermediate inlet or an internal pumping speed in the axial region of the inlet can be influenced.

Particularly in the context of an intermediate inlet, the internal pumping speed at the intermediate inlet typically differs from the pumping speed of the intermediate inlet itself. This becomes clear, for example, using an example of a common split-flow pump. Here, an intermediate inlet can be designed, for example, as a recess in the housing of a turbomolecular pump stage. This recess has a conductance that influences the suction speed of the intermediate inlet itself. However, this conductance has no influence in the axial area of the intermediate inlet within the housing. This is where the internal suction speed prevails. The goal here can be, in particular, to influence the internal suction speed at the relevant inlet. However, influencing the internal suction speed at the inlet can fundamentally also influence the suction speed of the inlet itself.

The blocking element is provided within a pump stage. This means that the pump stage has a pump-active element both upstream and downstream of the blocking element. The blocking element is in particular not arranged at the end of the relevant pump stage. In principle, several first digits can also be provided, i.e. H. the suction speed can be influenced in several places. Likewise, several blocking elements can be provided at a respective second location, for example to influence the suction speed at a first location or at several first locations.

The second location is spaced from the first location. For the present disclosure, this means that at least one pump-active element is provided between the first and second locations.

The second point can preferably be arranged downstream of the first point. The blocking element influences the suction speed in a simple and advantageous manner upstream of the same or the first point.

According to the invention it is provided that the, in particular internal, suction speed is influenced at the first point in such a way that there is a difference and/or a ratio between one partial pumping speed, in particular internal partial pumping speed, for a first gas and a partial pumping speed, in particular internal partial pumping speed, for a second gas is increased. This makes advantageous use of the fact that the blocking element can influence the partial suction speeds for different gases in different ways at the first point. By specifically arranging and designing the blocking element, the partial suction speeds can be specifically influenced so that the difference or the ratio between two partial suction speeds for different gases is as large as possible. By increasing the difference or the ratio of the partial pumping speeds, the quantitative ratio of the first gas flowing back against the pumping direction to the second gas flowing back changes in particular. In this way, for example, a kind of selection can be implemented. The larger the difference, the stronger the selection.

More generally, this idea and thus the invention also relates to a method for increasing the difference and/or a ratio between a partial pumping speed for a first gas and a partial pumping speed for a second gas, comprising a method of the type described above.

The difference can be increased effectively in particular when the first and second gas have a different molar mass. The first gas can preferably have a molar mass of more than 10 g/mol, in particular more than 20 g/mol. The first gas can be, for example, nitrogen, hereinafter also referred to as N2. Nitrogen has a molar mass of approximately 28 g/mol. The first gas can also be air, for example. The second gas can preferably have a molar mass of less than 10 g/mol, in particular less than 5 g/mol. The second gas can be, for example, helium, hereinafter also referred to as He. Helium has a molar mass of approximately 4 g/mol. The second gas can also be, for example be hydrogen. Hydrogen has a molar mass of approximately 2 g/mol. The second gas can be, for example, a test gas for leak detection.

Furthermore, not only a difference in the amount sense can be influenced, but also a difference in the sign sense. The increase in the difference in the signed sense means that the partial pumping speed for a first gas is greater than the partial pumping speed for a second gas by the highest possible value. The goal is also to ensure that the difference does not take on a negative sign.

It goes without saying that partial suction speeds for three or more gases can also be advantageously influenced in their difference and/or in relation to one another by the blocking element according to the invention.

According to the invention it is provided that the first point is arranged within a housing of the molecular vacuum pump, in a region directly connected to an inlet and/or in an axial region of an inlet. The inlet can preferably be an intermediate inlet. With the help of the blocking element at the second point, the suction speed effective at the first point, in particular internal, can be easily influenced in a targeted manner.

Furthermore, it is provided according to the invention that the second point or the blocking element is arranged outside an inlet area, in particular outside of all inlet areas. Generally preferably, the second point or the blocking element is provided within a housing of the molecular vacuum pump. Further generally preferred, the second point or the blocking element can be provided within a pump stage. This takes advantage of the fact that the blocking element in its immediate vicinity can cause a quite drastic local reduction in the suction speed. If the second digit in one Inlet area is arranged, this can lead to the suction speed at the relevant inlet being greatly reduced, which is often not desirable. However, if the blocking element is arranged at a certain distance from the inlet, the suction speed at this inlet can be influenced without a drastic reduction. This proves to be particularly advantageous in connection with the targeted influence of a difference or a ratio between partial suction speeds. Often it is not just the difference or ratio of the partial pumping speeds that is of interest, but also the level of the partial pumping speed in itself.

According to the invention, the blocking element is designed such that a partial suction speed for a first gas and a partial suction speed for a second gas at the second point are at least essentially the same. This is achieved according to the invention in that the blocking element has a pump-active structure. Simulations have shown that the difference in the partial suction speed at the first point can be increased particularly significantly through this further development. A deviation of at most 2 liters per second (L/s), preferably at most 1 L/s, is to be understood as being essentially the same.

The object of the invention is also achieved by a molecular vacuum pump according to the independent claim directed thereto. This teaches a molecular vacuum pump with at least one molecular pump stage, by means of which a gaseous medium can be conveyed along a flow path from an inlet to an outlet of the molecular vacuum pump, the pump stage being one Pumping direction and transverse to the pumping direction has a passage cross section, with a, in particular static, blocking element being provided, through which the passage cross section is locally reduced.

In an advantageous embodiment it is provided that the molecular vacuum pump comprises an intermediate inlet which is arranged within the pump stage. In a likewise advantageous example, an intermediate inlet can also be arranged between two pump stages. A molecular vacuum pump with an intermediate inlet is also called a split-flow pump. In such a case, the advantages according to the invention can be exploited particularly effectively.

According to a further development, it is provided that the blocking element is arranged in the pumping direction after an inlet, in particular after an intermediate inlet, preferably in a pumping stage which is arranged downstream of a first pumping stage in the pumping direction.

In a further embodiment, the blocking element is arranged outside an inlet area. This means that at least one pump-active element is arranged in the pumping direction between the relevant inlet and the blocking element. The blocking element can therefore be spaced in particular from an inlet area.

The blocking element can preferably be arranged outside each inlet area or not in an inlet area and/or can be spaced apart from all inlets. In particular, the blocking element can also be arranged outside one or each outlet area.

A blocking element in an inlet area, in particular immediately in front of an inlet area, of a molecular vacuum pump can serve to guide the inflowing gaseous medium and prevent backflow against the pumping direction to reduce. If, on the other hand, the blocking element is arranged outside the inlet area, at the inlet in particular the, in particular internal, suction speed for different gases can be influenced differently and in particular a difference and / or a ratio of a partial suction speed for a first gas to a partial suction speed for a second gas increase. This also influences the probability with which a given gas molecule flows back against the pumping direction, but not directly through a conductive function of the blocking element, but rather by influencing the suction speed at a first point through the blocking element at a second point. The blocking element therefore has a kind of long-distance effect with regard to the local suction speed at other points in the flow path. If the partial suction speeds for different gases are influenced differently at one point within the housing, the proportions of the different gases in the return flow in particular change. This ultimately achieves a selection of the different gases. The gases in question cannot be completely separated from each other in this way. Nevertheless, for certain applications it can be advantageous to change the proportions of gases in the return flow - even if only slightly.

The blocking element is arranged within a pump stage, i.e. between two pump-active elements of the pump stage. Preferably, the blocking element can be arranged in the pumping direction between two inlets or between an inlet and an outlet.

According to the invention it is provided that the blocking element is closed over an angular range with respect to a rotation axis of a pump rotor, specifically over an angular range of more than 180°, in particular more than 270°. In the remaining angular range, the blocking element has a pump-active structure. By means of a pump-active structure in the blocking element, the partial suction speeds for different gases in the blocking element, ie at the second point, can be dimensioned particularly similarly, at best at least essentially the same. This can result in a particularly strong influence on the pumping speed, in particular at another, i.e. first, point, in particular an increase in the difference or the ratio between two partial pumping speeds for different gases.

The pump-active structure can in particular have a number, in particular an effective number, of pump-active features and/or passages between pump-active features, the number preferably being at least 1 and/or at most 10. This range has proven to be particularly advantageous with regard to the highest possible difference in partial suction speed at the first point. A maximum number of 4 has also proven to be particularly advantageous.

The molecular vacuum pump can preferably comprise at least one of or any combination of turbomolecular pumping stage, Holweck pumping stage and/or Siegbahn pumping stage. The pump stages can in particular be connected in series. The pump stages in particular have rotors or rotor sections that are arranged on a common rotor shaft, or are preferably driven by a common rotor shaft.

The blocking element is arranged within a turbomolecular pump stage, a Holweck pump stage or a Siegbahn pump stage.

It Several blocking elements can also be provided, for example in different or similar pump stages.

In a turbomolecular pump stage, a pump-active element is formed by a turbo rotor disk or a turbo stator disk. A pump-active feature is formed by a turbo rotor blade or a turbo stator blade.

In a Holweck pump stage, a pump-active element is formed by an axial section with respect to a rotation axis of a pump rotor, with Holweck webs being arranged distributed over the, in particular at least essentially the entire, circumference in this axial section. A pump-active feature is formed by a Holweck web section.

In a Siegbahn pumping stage, a pump-active element is formed by a radial section with respect to a rotation axis of a pump rotor, with Siegbahn webs distributed over the, in particular at least substantially entire, circumference in this radial section. A pump-active feature is formed by a victory track web section.

The blocking element can, for example, also be arranged in one of several pump stages, in particular in order to influence the suction speed at a point, in particular a point within the housing that is directly connected to an inlet, which is arranged in or at another pump stage. It can therefore be provided, for example, that the molecular vacuum pump has a Holweck pump stage, within which a blocking element is arranged, the suction speed being influenced at an intermediate inlet, which is arranged within a turbomolecular pump stage upstream of the Holweck pump stage or between two turbomolecular pump stages upstream of the Holweck pump stage.

An example not according to the invention provides that the blocking element is arranged between two pump stages, in particular between a Holweck pump stage and a turbomolecular pump stage. This can also serve to influence the pumping speed at an intermediate inlet which is arranged within a turbomolecular pump stage upstream of the Holweck pump stage or between two turbomolecular pump stages upstream of the Holweck pump stage.

In principle, the blocking element can also be provided, for example, between two inlets, in particular between two intermediate inlets. For example, the blocking element can be arranged in a pump stage, before and after which an inlet or intermediate inlet is provided. A blocking element between two inlets can, for example, ensure that the compression of the pump stage changes or is influenced between the inlets. This influences the pressure ratio between the relevant inlets.

According to a technically simple example, the blocking element can be made of sheet metal, in particular if the blocking element is arranged in or on a turbomolecular pump stage. The blocking element can, for example, include pump-active features, e.g. turbostator blades, which are produced by stamping and/or bending.

In or on a Holweck pump stage or Siegbahn pump stage, the blocking element can be designed, for example, as a transverse wall which blocks one or more Holweck grooves or Siegbahn grooves. For example, several or all Holweck or Siegbahn grooves of a pump stage can be closed at an axial or radial position by a web perpendicular to the pumping direction, with only one groove or only individual grooves being designed normally - ie open.

The blocking element can basically be designed, for example, as a panel.

The invention further relates to a leak detector comprising a molecular vacuum pump of the type described above and a detection device, in particular for a test gas. The advantages according to the invention can be exploited particularly effectively in a leak detector. The leak detector can preferably be designed as a countercurrent leak detector. Helium or hydrogen can preferably be used as the test gas - especially in the case of hydrogen, for example in the form of a gas mixture which contains the test gas or hydrogen. The detection device can be designed, for example, as a mass spectrometer.

The molecular vacuum pump of the leak detector comprises a first inlet and an intermediate inlet, the first inlet being connected to the detection device and the intermediate inlet being connected or connectable to a vacuum system to be examined for leaks.

The blocking element is provided downstream of the intermediate inlet, with at least one pump-active element being provided in the pumping direction between the intermediate inlet and the blocking element.

The blocking element is therefore arranged in particular outside the area of the intermediate inlet and/or spaced apart from it.

The invention further relates to the use of a molecular vacuum pump of the type described above for searching for a leak in a vacuum system. A passage cross section is the open area within a pumping stage measured in cross section at a selected location along the pumping direction or flow path. The passage cross section is therefore in particular due to the The sum of the openings in the cross section in question is formed, through which gas particles to be conveyed can pass. In the case of a rotor-operated molecular vacuum pump, the passage cross section refers in particular to a cross section at a selected point along the rotor axis, with the cutting plane in particular running perpendicular to the rotor axis.

The passage cross section of the pump stage is defined in particular by one or more stator elements, in the case of a turbomolecular pump stage in particular stator disks, namely in particular one or more stator elements which are arranged upstream or downstream of the blocking element in the pumping direction. The pump stage can basically have a variable passage cross section along its axial extent. The local reduction caused by the blocking element is crucial.

According to the invention, the passage cross section is only reduced by the blocking element, but not completely blocked. The blocking element can, for example, cover part of the passage cross section. It therefore remains possible to convey gas through the pump stage past the blocking element and, for example, to a next pump stage.

The passage cross section is therefore formed in particular by the open area of a cross section through a rotor of the pump in the area of the pump stage. In a turbomolecular pump or pump stage, a passage cross section of a turbostator disk is limited, for example, radially outwards by a radially outer boundary of the turbostator blades. Inwards, the passage cross section is limited by a radially inner boundary of the turbostator blades, namely by a so-called blade base. The passage cross section has open sections separated in the circumferential direction by the blades. The same applies to a turbo rotor or a turbo rotor disk. In the case of a Holweck pump stage, the passage cross-section is, for example, to the outside or limited on the inside by a base of several Holweck grooves. In the opposite direction, i.e. inwards or outwards, the passage cross section is limited in particular by a Holweck rotor. The passage cross section has open sections separated in the circumferential direction by Holweck webs, namely the Holweck grooves. In general, the passage cross section in a Holweck pump stage essentially corresponds to the sum of the cross sections of the Holweck grooves. The same applies to Siegbahn pump stages in the radial direction.

In particular, the passage cross section through the blocking element can be reduced by at least 25%, in particular at least 50%, more preferably at least 75%, in particular based on the cross-sectional area of the passage cross section of the pump stage before and/or after the blocking element.

For example, an intermediate inlet of a multistage molecular vacuum pump is also referred to as an “interstage port” and a molecular vacuum pump with such an intermediate inlet is also referred to as a “splitflow pump”.

In particular, the passage cross section through the blocking element can be locally asymmetrical, in particular with respect to a rotor axis of the pump stage. For example, the blocking element can be arranged such that on a side of a rotor shaft of the pump stage facing the intermediate inlet, the blocking element blocks a larger proportion of the passage cross section than on a side of the rotor facing away from the intermediate inlet, or vice versa. In general, the blocking element can be arranged on a side of the rotor shaft facing or away from the intermediate inlet. For example, the blocking element can only be arranged in a partial angular range with respect to the rotor axis, which in particular can be assigned or not assigned to the intermediate inlet. The blocking element can change the passage cross section, for example block an area that lies radially between the rotor axis and the intermediate inlet.

For example, it can be provided that the blocking element is designed to be impermeable at least in a peripheral section assigned or not assigned to the intermediate inlet, in particular essentially only in this peripheral section. A region radially opposite the intermediate inlet or a region radially facing the intermediate inlet can in particular be designed to be permeable and pump-active. In the area radially opposite or facing the intermediate inlet, the stator can be particularly permeable and generally designed like a “normal” stator.

The geometry of the blocking element can, for example, be changeable. Depending on the selected geometry, different performance in terms of suction speed can be set.

According to one embodiment, it is provided that the blocking element is designed as a wall and/or as a continuous surface element and/or extends transversely to the pumping direction. This represents a structurally simple way to achieve the advantages according to the invention. The blocking element can extend in particular perpendicular and/or transversely to the pumping direction and/or to the rotor axis. A surface element or a wall can, for example, be arranged parallel to a boundary of the intermediate inlet and/or obliquely or perpendicularly with respect to a rotor axis.

In some embodiments, the blocking element extends in the radial direction only over a part of the passage cross section of the pump stage, in particular in relation to the adjacent, in particular upstream and/or downstream, passage cross section before or after the local reduction. In particular, the blocking element can cover and/or a radially inner part do not cover a radially outer part. For example, a combination with a blocking element or a section of the same blocking element in a different circumferential area extending over the entire radial width is also possible.

According to one embodiment it is provided that the blocking element is designed as part of a turbo stator disk. In principle, the blocking element can, for example, be connected directly to a stator disk, in particular a partial stator disk, and/or be axially assigned to such. Axially assigned means that the blocking element is at least partially arranged in the same axial region as the stator disk or partial stator disk. In particular, the blocking element can replace a section of the turbo stator disk that faces or faces away from the intermediate inlet. Viewed in cross section and at the axial height of the blocking element, stator blades can be provided, for example, on one side of the rotor shaft, in particular facing or away from the intermediate inlet, while on another side of the rotor shaft facing the intermediate inlet, the blocking element or a closed area thereof and in particular none Stator blades are provided.

According to a structurally simple exemplary embodiment, the blocking element can be designed as a sheet metal. Turbostator disks are often also designed as sheet metal parts and the blocking element can generally be manufactured or designed in a similar way to a turbostator disk, but no separated blades are provided, particularly in a closed area of the blocking element.

In a further development it is provided that the blocking element defines a, in particular radially inner, blade base for one or more stator blades. In particular, one defined by the blocking element Blade base diameter must be larger than the blade base diameter of an upstream or downstream rotor and/or stator disk, in particular at least 20% larger.

Preferably, the blocking element is designed to be flat at least essentially and at least with a closed area of the blocking element. The blocking element can, for example, also be designed in the shape of a shell and/or funnel, in particular in the shape of a partial ring, partial shell and/or a partial funnel, the term “partial” referring in particular to an angular range around the rotor shaft.

In general, the pump can, for example, have a pump-active rotor section upstream of the intermediate inlet in relation to the pumping direction and a pump-active rotor section downstream in relation to the pumping direction, in which case both rotor sections can in particular be connected to the same rotor shaft and/or connected in series. In general, the molecular vacuum pump can, for example, have only one rotor shaft, whereby in particular all pump stages and pump stage sections can be driven by the rotor shaft and/or can be connected in series.

In general, the intermediate inlet can preferably open into an axial region, in particular in a pump housing, over which the pump stage or the pump stage section upstream of the intermediate inlet is connected in series with a pump stage or the pump stage section downstream of the intermediate inlet. This axial region can be, for example, an intermediate stage region or an axial region within a pump stage, for example an axial region of a turbo rotor disk. In general, gas can be conveyed in particular via the axial region into which the intermediate inlet opens and/or across the intermediate stage region.

It is understood that the methods described herein can also be developed in accordance with the embodiments and individual features described in relation to the devices and vice versa.

Fig. 1

eine perspektivische Ansicht einer Turbomolekularpumpe,

Fig. 2

eine Ansicht der Unterseite der Turbomolekularpumpe von Fig. 1,

Fig. 3

einen Querschnitt der Turbomolekularpumpe längs der in Fig. 2 gezeigten Schnittlinie A-A,

Fig. 4

eine Querschnittsansicht der Turbomolekularpumpe längs der in Fig. 2 gezeigten Schnittlinie B-B,

Fig. 5

eine Querschnittsansicht der Turbomolekularpumpe längs der in Fig. 2 gezeigten Schnittlinie C-C,

Fig. 6

eine Auftragung eines internen Saugvermögensverlaufs einer Molekularvakuumpumpe,

Fig. 7

eine Molekularvakuumpumpe,

Fig. 8

eine Auftragung eines internen Saugvermögensverlaufs einer Molekularvakuumpumpe mit einem Blockierelement,

Fig. 9

eine Molekularvakuumpumpe mit Blockierelement,

Fig. 10

ein Blockierelement,

Fig. 11

ein erfindungsgemäßes woitoroo Blockierelement,

Fig. 12

eine Auftragung eines internen Saugvermögensverlaufs einer Molekularvakuumpumpe mit einem Blockierelement,

Fig. 13

ein Lecksuchgerät.

The invention is described below by way of example using advantageous embodiments with reference to the attached figures. Show it schematically:

Fig. 1

a perspective view of a turbomolecular pump,

Fig. 2

a view of the bottom of the turbomolecular pump of Fig. 1 ,

Fig. 3

a cross section of the turbomolecular pump along the in Fig. 2 shown section line AA,

Fig. 4

a cross-sectional view of the turbomolecular pump along the in Fig. 2 shown cutting line BB,

Fig. 5

a cross-sectional view of the turbomolecular pump along the in Fig. 2 shown cutting line CC,

Fig. 6

a plot of an internal pumping speed curve of a molecular vacuum pump,

Fig. 7

a molecular vacuum pump,

Fig. 8

a plot of an internal pumping speed curve of a molecular vacuum pump with a blocking element,

Fig. 9

a molecular vacuum pump with blocking element,

Fig. 10

a blocking element,

Fig. 11

a woitoroo blocking element according to the invention,

Fig. 12

a plot of an internal pumping speed curve of a molecular vacuum pump with a blocking element,

Fig. 13

a leak detector.

In the Fig. 1 Turbomolecular pump 111 shown comprises a pump inlet 115 surrounded by an inlet flange 113, to which a recipient, not shown, can be connected in a manner known per se. The gas from the recipient can be sucked out of the recipient via the pump inlet 115 and conveyed through the pump to a pump outlet 117, to which a backing pump, such as a rotary vane pump, can be connected.

The inlet flange 113 forms the alignment of the vacuum pump according to Fig. 1 the upper end of the housing 119 of the vacuum pump 111. The housing 119 comprises a lower part 121, on which an electronics housing 123 is arranged laterally. Electrical and/or electronic components of the vacuum pump 111 are accommodated in the electronics housing 123, for example for operating an electric motor 125 arranged in the vacuum pump (see also Fig. 3 ). Several connections 127 for accessories are provided on the electronics housing 123. In addition, a data interface 129, for example according to the RS485 standard, and a power supply connection 131 are arranged on the electronics housing 123.

There are also turbomolecular pumps that do not have such an attached electronics housing, but are connected to external drive electronics.

A flood inlet 133, in particular in the form of a flood valve, is provided on the housing 119 of the turbomolecular pump 111, via which the vacuum pump 111 can be flooded. In the area of the lower part 121 there is also a sealing gas connection 135, which is also referred to as a flushing gas connection, via which flushing gas is supplied to protect the electric motor 125 (see e.g Fig. 3 ) can be admitted into the engine compartment 137, in which the electric motor 125 is accommodated in the vacuum pump 111, in front of the gas delivered by the pump. Two coolant connections 139 are also arranged in the lower part 121, one of the coolant connections being provided as an inlet and the other coolant connection being provided as an outlet for coolant, which can be directed into the vacuum pump for cooling purposes. Other existing turbomolecular vacuum pumps (not shown) operate exclusively with air cooling.

The lower side 141 of the vacuum pump can serve as a standing surface, so that the vacuum pump 111 can be operated standing on the underside 141. The vacuum pump 111 can also be attached to a recipient via the inlet flange 113 and can therefore be operated hanging, so to speak. In addition, the vacuum pump 111 can be designed so that it can be put into operation even if it is oriented in a different way than in Fig. 1 is shown. Embodiments of the vacuum pump can also be implemented in which the underside 141 can be arranged not facing downwards, but facing to the side or facing upwards. In principle, any angle is possible.

Other existing turbomolecular vacuum pumps (not shown), which are in particular larger than the pump shown here, cannot be operated standing.

At the bottom 141, the in Fig. 2 is shown, various screws 143 are arranged, by means of which components of the vacuum pump that are not specified here are fastened to one another. For example, a bearing cover 145 is attached to the underside 141.

Fastening holes 147 are also arranged on the underside 141, via which the pump 111 can be fastened to a support surface, for example. This is not possible with other existing turbomolecular vacuum pumps (not shown), which are in particular larger than the pump shown here.

In the Figures 2 to 5 a coolant line 148 is shown, in which the coolant introduced and discharged via the coolant connections 139 can circulate.

Like the sectional views of the Figures 3 to 5 show, the vacuum pump comprises several process gas pumping stages for conveying the process gas present at the pump inlet 115 to the pump outlet 117.

A rotor 149 is arranged in the housing 119 and has a rotor shaft 153 which can be rotated about a rotation axis 151.

The turbomolecular pump 111 comprises a plurality of turbomolecular pump stages connected in series with one another and having a plurality of radial rotor disks 155 attached to the rotor shaft 153 and stator disks 157 arranged between the rotor disks 155 and fixed in the housing 119 A rotor disk 155 and an adjacent stator disk 157 each form a turbomolecular pump stage. The stator disks 157 are held at a desired axial distance from one another by spacer rings 159.

The vacuum pump also includes Holweck pump stages that are arranged one inside the other in the radial direction and are effectively connected in series. There are other turbomolecular vacuum pumps (not shown) that do not have Holweck pump stages.

The rotor of the Holweck pump stages includes a rotor hub 161 arranged on the rotor shaft 153 and two cylindrical jacket-shaped Holweck rotor sleeves 163, 165 which are fastened to the rotor hub 161 and supported by it, which are oriented coaxially to the axis of rotation 151 and nested in one another in the radial direction. Furthermore, two cylindrical jacket-shaped Holweck stator sleeves 167, 169 are provided, which are also oriented coaxially to the axis of rotation 151 and are nested within one another when viewed in the radial direction.

The pump-active surfaces of the Holweck pump stages are formed by the lateral surfaces, i.e. by the radial inner and/or outer surfaces, of the Holweck rotor sleeves 163, 165 and the Holweck stator sleeves 167, 169. The radial inner surface of the outer Holweck stator sleeve 167 lies opposite the radial outer surface of the outer Holweck rotor sleeve 163, forming a radial Holweck gap 171 and with this forms the first Holweck pump stage following the turbomolecular pumps. The radial inner surface of the outer Holweck rotor sleeve 163 faces the radial outer surface of the inner Holweck stator sleeve 169 to form a radial Holweck gap 173 and forms a second Holweck pump stage with this. The radial inner surface of the inner Holweck stator sleeve 169 lies opposite the radial outer surface of the inner Holweck rotor sleeve 165, forming a radial Holweck gap 175 and with this forms the third Holweck pump stage.

At the lower end of the Holweck rotor sleeve 163, a radially extending channel can be provided, via which the radially outer Holweck gap 171 is connected to the middle Holweck gap 173. In addition, a radially extending channel can be provided at the upper end of the inner Holweck stator sleeve 169, via which the middle Holweck gap 173 is connected to the radially inner Holweck gap 175. This means that the nested Holweck pump stages are connected in series with one another. At the lower end of the radially inner Holweck rotor sleeve 165, a connecting channel 179 to the outlet 117 can also be provided.

The above-mentioned pump-active surfaces of the Holweck stator sleeves 167, 169 each have a plurality of Holweck grooves running spirally around the axis of rotation 151 in the axial direction, while the opposite lateral surfaces of the Holweck rotor sleeves 163, 165 are smooth and the gas is used to operate the Drive vacuum pump 111 into the Holweck grooves.

To rotatably support the rotor shaft 153, a rolling bearing 181 is provided in the area of the pump outlet 117 and a permanent magnet bearing 183 in the area of the pump inlet 115.

In the area of the rolling bearing 181, a conical injection nut 185 with an outer diameter increasing towards the rolling bearing 181 is provided on the rotor shaft 153. The injection nut 185 is in sliding contact with at least one wiper of an operating medium storage. In other existing turbomolecular vacuum pumps (not shown), an injection screw may be provided instead of an injection nut. Since different designs are possible, the term “spray tip” is also used in this context.

The operating medium storage comprises several absorbent disks 187 stacked on top of one another, which are soaked with an operating medium for the rolling bearing 181, for example with a lubricant.

During operation of the vacuum pump 111, the operating fluid is transferred by capillary action from the operating fluid storage via the wiper to the rotating injection nut 185 and, as a result of the centrifugal force, is conveyed along the injection nut 185 in the direction of the increasing outer diameter of the injection nut 185 to the rolling bearing 181, where it e.g. fulfills a lubricating function. The rolling bearing 181 and the operating fluid storage are enclosed in the vacuum pump by a trough-shaped insert 189 and the bearing cover 145.

The permanent magnet bearing 183 comprises a rotor-side bearing half 191 and a stator-side bearing half 193, each of which comprises a ring stack made up of a plurality of permanent magnetic rings 195, 197 stacked on top of one another in the axial direction. The ring magnets 195, 197 lie opposite one another to form a radial bearing gap 199, with the rotor-side ring magnets 195 being arranged radially on the outside and the stator-side ring magnets 197 being arranged radially on the inside. The magnetic field present in the bearing gap 199 causes magnetic repulsion forces between the ring magnets 195, 197, which cause the rotor shaft 153 to be supported radially. The rotor-side ring magnets 195 are carried by a carrier section 201 of the rotor shaft 153, which surrounds the ring magnets 195 on the radial outside. The stator-side ring magnets 197 are supported by a stator-side support section 203, which extends through the ring magnets 197 and is suspended on radial struts 205 of the housing 119. The rotor-side ring magnets 195 are fixed parallel to the rotation axis 151 by a cover element 207 coupled to the carrier section 201. The stator-side ring magnets 197 are parallel to the rotation axis 151 in one direction through a fastening ring 209 connected to the carrier section 203 and one connected to the carrier section 203 connected fastening ring 211 set. A disc spring 213 can also be provided between the fastening ring 211 and the ring magnets 197.

An emergency or safety bearing 215 is provided within the magnetic bearing, which runs empty without contact during normal operation of the vacuum pump 111 and only comes into engagement when there is an excessive radial deflection of the rotor 149 relative to the stator to form a radial stop for the rotor 149 to form so that a collision of the rotor-side structures with the stator-side structures is prevented. The backup bearing 215 is designed as an unlubricated rolling bearing and forms a radial gap with the rotor 149 and/or the stator, which causes the backup bearing 215 to be disengaged during normal pumping operation. The radial deflection at which the backup bearing 215 comes into engagement is large enough so that the backup bearing 215 does not come into engagement during normal operation of the vacuum pump, and at the same time small enough so that a collision of the rotor-side structures with the stator-side structures occurs under all circumstances is prevented.

The vacuum pump 111 includes the electric motor 125 for rotating the rotor 149. The armature of the electric motor 125 is formed by the rotor 149, the rotor shaft 153 of which extends through the motor stator 217. A permanent magnet arrangement can be arranged radially on the outside or embedded on the section of the rotor shaft 153 which extends through the motor stator 217. Between the motor stator 217 and the section of the rotor 149 that extends through the motor stator 217, a gap 219 is arranged, which comprises a radial motor gap through which the motor stator 217 and the permanent magnet arrangement can magnetically influence each other for transmitting the drive torque.

The motor stator 217 is fixed in the housing within the engine compartment 137 provided for the electric motor 125. A sealing gas, which is also referred to as purging gas and which can be, for example, air or nitrogen, can reach the engine compartment 137 via the sealing gas connection 135. The barrier gas can be used to protect the electric motor 125 from process gas, for example from corrosive components of the process gas. The engine compartment 137 can also be evacuated via the pump outlet 117, i.e. in the engine compartment 137 there is at least approximately the vacuum pressure caused by the backing vacuum pump connected to the pump outlet 117.

A so-called and known labyrinth seal 223 can also be provided between the rotor hub 161 and a wall 221 delimiting the engine compartment 137, in particular in order to achieve a better sealing of the engine compartment 217 compared to the Holweck pump stages located radially outside.

Some of the pumps and systems described below are presented in a highly schematic and simplified manner. For the purpose of practical implementation, they can advantageously be implemented with one or more features of the pump described above. Likewise, the pump described above can advantageously be equipped with a blocking element, in particular instead of one of the stator disks shown.

In Fig. 6 a plot of two partial pumping speeds for different gases within an exemplary molecular vacuum pump 250 is shown, which is shown in Fig. 7 is shown. The molecular vacuum pump 250 includes a turbo pump stage 252 and a Holweck pump stage 254.

The ordinate of the plot in Fig. 6 is assigned to the pumping speed S in L/s. The abscissa is assigned to a point i under consideration along the flow path of the molecular vacuum pump 250. The turbo pump stage 250 includes 16 Slices, each representing a "spot" in the sense of the application of the Fig. 6 represent. The Holweck pump stage 254 as a whole represents a point in the sense of the application of the Fig. 6 All points i are arranged within the housing of the molecular vacuum pump 250, not shown here. The plot shows the course of the internal partial pumping speeds for the different gases.

The numbering of the points in the flow path is carried out in the opposite direction to the pumping direction. The turbo rotor disk at point 17 forms the high vacuum side end of the molecular vacuum pump 250, whereas the Holweck pump stage 254 at point 1 forms the pressure side end of the molecular vacuum pump 250. The pumping direction is therefore in Figs. 6 and 7 from right to left. Turbo stator disks have even numbers, whereas turbo rotor disks have odd numbers, the latter not being listed separately for the sake of clarity. In Fig. 7 However, to make it easier to understand, positions 1 and 17 are marked.

In general, the pumping speed S at the high vacuum side end of the molecular pump 250, right in Fig. 6 , quite large and takes to the pressure end of the molecular vacuum pump 250, in Fig. 6 to the left, down.

In the Fig. 6 The pumping speed curves shown relate to the partial pumping speeds for helium and nitrogen. Accordingly, the pumping speed curves are designated S _N2 or S _He . These pumping speed curves - like the pumping speed curves described below - were determined by simulation.

The molecular vacuum pump 250 includes a first inlet 256 in the pumping direction, which opens at point 17 or at the high-vacuum side turbo rotor disk. The molecular vacuum pump 250 also includes one Intermediate inlet 258, which opens at point 11 or at the corresponding turbo rotor disk.

Inlets 256 and 258 are both in Fig. 6 as well as in Fig. 7 indicated. Furthermore, in Fig. 6 a difference 260 between the partial pumping speeds for helium and nitrogen at the intermediate connection 258 or at point 11 is indicated. The difference 260 therefore corresponds to ΔS ₁₁ = S _N2;11 - S _He;11 .

The 8 and 9 show to the Figs. 6 and 7 similar representations, why regarding the 8 and 9 only special features are discussed. The molecular vacuum pump 250 under consideration is basically like that of Fig. 7 built up. At point 6, however, no ordinary turbo stator disk is provided, but rather a static blocking element 262. The blocking element 262 is both in Fig. 8 as well as in Fig. 9 indicated.

The blocking element 262 causes a local reduction in the passage cross section of the molecular vacuum pump 250. This is achieved, for example, by the blocking element 262 being designed in some areas as a closed disk and in some areas as an at least partially open disk, as shown in FIG Fig. 9 is indicated by a solid line on the one hand of the rotor shaft 264 or a dashed line on the other hand of the rotor shaft 264.

How out Fig. 8 As can be seen, the partial suction speeds S _N2 and S _He are greatly reduced at point 6 and at blocking element 262, respectively. This corresponds to the expectations of those skilled in the art, since the blocking element 262 locally reduces the passage cross section of the turbo pump stage 252. It has also been shown that the pumping speeds S _N2 and S _He are also influenced at other points along the flow path, in particular at points that are spaced from the blocking element 262. This emerges from a comparison of the Fig. 6 and 8th . It has also been shown that the partial pumping speeds S _N2 and S _He is not influenced in the same way, but differently. It was recognized that in general a blocking element 262 can be used to specifically influence a suction speed at a location different from the location of the blocking element 262 and that in particular the different influence on partial suction speeds for different gases can be exploited in order to achieve a difference and/or or to specifically influence a ratio between the partial suction speeds.

In particular, the partial suction speeds S _N2;11 and S _He;11 were influenced by the blocking element 262 in such a way that the difference 260 between these two partial suction speeds compared to Fig. 6 or to the molecular vacuum pump 250 without blocking element Fig. 7 was enlarged. At the intermediate inlet 258, the partial suction speed for nitrogen was ultimately increased relative to the partial suction speed for helium.

In Fig. 10 an exemplary blocking element 262 is shown. The viewer's line of sight is parallel to the rotor shaft. The blocking element 262 is designed as a disk which is closed over an angular range with respect to the rotor shaft. The closed angle range 264 extends here over approximately 270°. In the remaining angular range 266, the blocking element 262 is simply open. The area 266 is therefore a permeable area. The blocking element 262 shown here forms a particularly simple embodiment. The pumping speed curves according to Fig. 8 are based in particular on such a blocking element 262.

In its middle, the blocking element 262 has an in Fig. 10 free central area 268, through which the rotor shaft extends in the assembled state. The central region 268 therefore does not form an open passage cross section. However, this is only formed by the angular range 266. Nevertheless, an open central area can also be larger than the rotor shaft, for example be so that a radial area between the blocking element and the rotor shaft is open or permeable. This concerns the inner circumference of the blocking element. It goes without saying that this also applies to its outer circumference, ie an open radial area can also be provided on the outer circumference.

In Fig. 11 an embodiment of a blocking element 262 according to the invention is shown in perspective. The blocking element 262 of Fig. 11 includes a closed angular range 264, which here is greater than 300°. In an area 270, the blocking element 262 is designed to be permeable, but in contrast to the area 266, it points in Fig. 10 a pump-active structure. The pump-active structure is formed here by turbo stator blades 272.

Specifically, the pump-active structure or region 270 has turbostator blades 272 with two passages 274 in between. The turbo stator blade 272.2 is designed, so to speak, as a “normal” turbo stator blade, in particular it forms a complete turbo stator blade. The turbo stator blades 272.1 and 272.3, on the other hand, are only designed as partial or “half” turbo stator blades. Thus, the pump-active structure of the blocking element 262 effectively has two turbo stator blades, which corresponds to the number of passages 274 between the turbo stator blades 272.

The pump-active structure of the blocking element 262 causes a relative equalization of the partial suction speeds for different gases in the area of the blocking element 262.

Fig. 12 shows a plot of the partial pumping speeds for nitrogen and helium in a pump according to Fig. 9 , wherein the blocking element 262 according to Fig. 11 is designed and is also provided at point 6. A comparison of the plots of the Fig. 8 and 12 at point 6 shows that with the blocking element 262 according to Fig. 11 the partial pumping speeds S _N2 and S _He at the point of Blocking element 262, here at point 6, are more similar than the blocking element 262 according to Fig. 10 or without a pump-active structure, in particular at least essentially the same.

In addition, a comparison of the plots shows Fig. 8 and 12 at point 11 or at the intermediate inlet 258, that the difference 260 between the partial suction speed in Fig. 12 is larger than this in Fig. 8 the case is. The pump-active structure here ensures a further increase in the difference 260 of the partial pumping speed or a further increase in the partial pumping speed S _N2;11 relative to the partial pumping speed S _H2;11 .

In Fig. 13 a leak detector 280 is shown. The leak detector 280 includes a molecular vacuum pump 282, a detection device 284, which is designed as a mass spectrometer, and a connection 286 for a vacuum system, not shown here, which is to be checked for leaks.

The molecular vacuum pump 282 is designed as a split-flow pump. It includes a first inlet 288, an intermediate inlet 290, a further intermediate inlet 292 and an outlet 294.

The molecular vacuum pump 282 includes a turbo pump stage 296 and a Holweck pump stage 298. A pumping direction and a flow path run from the first inlet 288 to the outlet 294. The intermediate inlet 290 opens into the turbo pump stage 296. The intermediate inlet 292 opens at the entrance of the Holweck pump stage 268. The outlet 294 opens at End of Holweck pump stage 298.

The leak detector 280 further comprises a backing vacuum pump 300. The connection 286 is connected in particular to the intermediate inlets 290 and 292 via a line system and the backing vacuum pump 300 is connected in particular to the outlet 294. The line system is also designed and can be flexibly controlled by valves 302 in such a way that both the connection 286 and the backing vacuum pump 300 can be connected to or separated from the intermediate inlets 290 and 292 as well as the outlet 294 in essentially any way.

The leak detector 280 is operated, for example, with helium as a test gas. Alternatively, for example, hydrogen or a gas mixture containing hydrogen can be used as a test gas. The present descriptions of the figures largely refer only to helium, but apply accordingly to hydrogen.

When searching for a leak, helium is distributed in the area of the vacuum system to be examined for leaks, not shown here, and the vacuum system is evacuated via connection 286. If the vacuum system has a leak, helium - in addition to the ambient air - gets into the vacuum system and to the connection 286. This is in particular connected to the intermediate inlet 290, so that the helium, together with the gas components of the ambient air, reaches the intermediate inlet 290 and into the molecular vacuum pump 282 .

The detection device 284 is used to detect the helium. A certain part of the helium will flow from the intermediate inlet 290 counter to the pumping direction and reach the detection device 284 via the first inlet 288. For this reason, a leak detector of the type shown here is also referred to as a countercurrent leak detector.

In principle, certain amounts of air components will also flow counter to the pumping direction and reach the detection device 284. These can affect the detection accuracy for helium. Since air consists largely of nitrogen, this is given priority here. To To improve the detection accuracy of the detection device 284 with regard to helium, it would be advantageous if the largest possible proportion of nitrogen is pumped out in the pumping direction to the outlet 294, while the largest possible proportion of helium reaches the detection device 284 counter to the pumping direction.

The molecular vacuum pump 282 is equipped with a blocking element 262. This is arranged at a location downstream of the intermediate inlet 290 and at a distance from it. Specifically, several pump-active elements are provided in the pumping direction between the blocking element 262 and the intermediate inlet 290.

The blocking element 262 causes the partial suction speed for nitrogen to be increased relative to the partial suction speed for helium at the location of the intermediate inlet 290 with respect to the flow path, in particular that the difference between these partial suction speeds is increased. This is done in a similar way as with regard to the Fig. 8 and 12 for the intermediate inlet 258 or point 11 is described.

By changing the partial pumping speeds for nitrogen and helium relative to one another, the ratio of backflowing helium to backflowing nitrogen also changes. In particular, a partial suction speed for nitrogen at the intermediate inlet 290, which is large relative to the partial suction speed for helium, causes a large part of the nitrogen to be transported away in the pumping direction and only a small part of the nitrogen to flow counter to the pumping direction. Conversely, this causes a small part of the helium to be transported away in the pumping direction and a large part of the helium to flow in the opposite direction to the pumping direction. The quantitative ratio of backflowing helium to backflowing nitrogen is thus improved and the detection accuracy of the leak detector 280 is thereby improved.

Reference symbol list

111

Turbomolecular pump

113

inlet flange

115

Pump inlet

117

Pump outlet

119

Housing

121

Bottom part

123

Electronics housing

125

Electric motor

127

Accessory connection

129

Data interface

131

Power supply connection

133

Flood inlet

135

Sealing gas connection

137

Engine compartment

139

Coolant connection

141

bottom

143

screw

145

Bearing cap

147

mounting hole

148

Coolant line

149

rotor

151

Axis of rotation

153

Rotor shaft

155

Rotor disc

157

stator disk

159

Spacer ring

161

Rotor hub

163

Holweck rotor sleeve

165

Holweck rotor sleeve

167

Holweck stator sleeve

169

Holweck stator sleeve

171

Holweck gap

173

Holweck gap

175

Holweck gap

179

connection channel

181

roller bearing

183

Permanent magnet bearings

185

Injection nut

187

disc

189

Mission

191

rotor side bearing half

193

stator side bearing half

195

Ring magnet

197

Ring magnet

199

Bearing gap

201

Support section

203

Support section

205

radial strut

207

Lid element

209

Support ring

211

Fastening ring

213

Disc spring

215

Emergency or detention camp

217

Motor stator

219

space

221

wall

223

Labyrinth seal

250

Molecular vacuum pump

252

Turbo pump stage

254

Holweck pump stage

256

first entrance

258

Intermediate entry

260

difference

262

Blocking element

264

closed area

266

permeable area

268

Central area

270

permeable area

272

Turbo stator blade

274

passage

280

Leak detector

282

Molecular vacuum pump

284

Detection device

286

Connection

288

first entrance

290

Intermediate entry

292

Intermediate entry

294

outlet

296

Turbo pump stage

298

Holweck pump stage

300

Backing pump

302

Valve

Claims (10)

1. A method of influencing the suction capacity, in particular an internal suction capacity, of a molecular vacuum pump (250, 280) which comprises at least one molecular pump stage (252, 254, 296, 298) by means of which a gaseous medium can be conveyed along a flow path from an inlet (256, 258, 288, 290) to an outlet of the molecular vacuum pump (250, 280),

   wherein the pump stage (252, 254, 296, 298) has a pumping direction and a passage cross-section transverse to the pumping direction,

   wherein the influencing of the suction capacity takes place at a first position in the flow path of the molecular vacuum pump (250, 280), namely by providing a blocking element (262) at a second position, which is different from the first position, in the flow path of the molecular vacuum pump (250, 280), by which blocking element (262) the passage cross-section is locally reduced,

   wherein the blocking element (262) is configured such that a partial suction capacity for a first gas and a partial suction capacity for a second gas are at least substantially equal at the second position,

   wherein the second position is spaced apart from the first position,

   wherein the first position is arranged within a housing of the molecular vacuum pump (250), in a region directly connected to an inlet (258, 256, 288, 290) and/or in an axial region of an inlet (258, 256, 288, 290), in particular an intermediate inlet, and wherein the second position is arranged outside an inlet region, and wherein the suction capacity, in particular an internal suction capacity, is influenced at the first position such that a difference and/or a ratio between a partial suction capacity for a first gas and a partial suction capacity for a second gas is increased there.
2. A method in accordance with claim 1,
   wherein the second position is arranged downstream of the first position.
3. A method in accordance with claim 1,

   wherein the first gas has a molar mass of more than 10 g/mol, in particular of more than 20 g/mol, and/or

   wherein the second gas has a molar mass of less than 10 g/mol, in particular less than 5 g/mol, and/or

   wherein the first gas is nitrogen and/or air and/or

   wherein the second gas is helium and/or hydrogen.
4. A molecular vacuum pump (282), in particular a turbomolecular pump, comprising

   at least one molecular pump stage (252, 254, 296, 298) by means of which a gaseous medium can be conveyed along a flow path from an inlet (256, 258, 288, 290) to an outlet (294) of the molecular vacuum pump (250, 282), wherein the pump stage (252, 254, 296, 298) has a pumping direction and a passage cross-section transverse to the pumping direction,

   wherein a blocking element (262), in particular a static blocking element, is provided by which the passage cross-section is locally reduced, wherein the blocking element (262) is arranged within a pump stage (252, 254, 296, 298), characterized in that

   the blocking element (262) is closed over an angular region (264) of more than 180° with respect to an axis of rotation of a pump rotor, in particular over an angular region of more than 270°,

   wherein the blocking element (262) has a pump-active structure (270) in the remainder of the angular region.
5. A molecular vacuum pump (250, 282) in accordance with claim 4,
   wherein the molecular vacuum pump (250, 282) comprises an intermediate inlet (258, 290) which is arranged within the pump stage (252, 296) or between two pump stages (252, 296).
6. A molecular vacuum pump (250, 282) in accordance with claim 4 or 5,
   wherein the blocking element (262) is arranged downstream of an inlet (256, 258, 288, 290), in particular downstream of an intermediate inlet, in the pumping direction.
7. A molecular vacuum pump (250, 282) in accordance with at least one of the claims 4 to 6,
   wherein the blocking element (262) is arranged outside an inlet region.
8. A molecular vacuum pump (282) in accordance with at least one of the claims 4 to 7,
   wherein the pump-active structure has a number, in particular an effective number, of pump-active features (272), wherein the number is at least 1 and/or at most 10, in particular at most 4.
9. A leak detector comprising:

   a molecular vacuum pump (282) in accordance with any one of the claims 4 to 8; and

   a detection device (284) for detecting a test gas,

   wherein the molecular vacuum pump (282) comprises a first inlet (288) and

   an intermediate inlet (290),

   wherein the first inlet (288) is connected to the detection device (284), in particular a mass spectrometer,

   wherein the intermediate inlet (290) is connected or connectable to a vacuum system to be inspected for leaks,

   wherein the blocking element (262) is provided downstream of the intermediate inlet (290), and

   wherein at least one pump-active element is provided between the intermediate inlet (290) and the blocking element (262) in the pumping direction.
10. Use of a molecular vacuum pump in accordance with any one of the claims 4 to 8 for finding a leak in a vacuum system.

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