DEVICE AND METHOD FOR LEAK DETECTION

Description

[0001] The invention relates to a device for leak detection using the countercurrent vacuum method, comprising a vacuum pump unit that can be connected to a test object to be evacuated and which includes a turbo vacuum pump with a turbo pump section formed by one or more turbo pump stages, and a detector, in particular a mass spectrometer, for detecting a test gas, in particular helium, wherein the turbo vacuum pump is connected to the detector via at least one axial and / or radial suction inlet and has a test gas inlet downstream of the suction inlet, and wherein at least a part of the turbo pump section is located between the suction inlet and the test gas inlet in the pumping direction of the turbo vacuum pump.

[0002] Furthermore, the invention relates to a method for leak detection using the vacuum method in the countercurrent principle by means of a leak detection device comprising a vacuum pump unit and a detector, wherein the vacuum pump unit can be connected to a test object to be evacuated and comprises a turbo vacuum pump with a turbo pump section formed by one or more turbo pump stages, in particular by means of a leak detection device as disclosed herein.

[0003] For the sake of simplicity, the word component "Turbo..." is used within the context of this disclosure as a shortened form of "turbomolecular...", i.e., when, for example, a turbo vacuum pump or a turbo pump stage is mentioned, then a turbomolecular pump or a turbomolecular pump stage is to be understood.

[0004] The concept of leak detection using the countercurrent vacuum method is fundamentally established in vacuum technology. The test object is either the component itself, also referred to as the "test specimen," which requires that this component can be evacuated to a certain vacuum pressure, or it is a vacuum chamber into which the component to be tested is placed. In the latter case, it is not the component itself, but the vacuum chamber that is evacuated. In both cases, the detector detects the test gas entering the vacuum; more precisely, the test gas flow is measured and displayed, for example, as a so-called leak rate.

[0005] Various types of leak detectors, particularly helium leak detectors, are generally known to those skilled in the art. The countercurrent principle discussed here, and the countercurrent leak detectors used for it, are also part of the specialized knowledge in the field of vacuum technology. Reference is made in particular to the relevant technical literature, specifically the "Wutz Handbook of Vacuum Technology (ed. Karl Jousten)," 11th edition, Springer Vieweg, and in particular to chapters 14.4 "Leak Detectors," 19 "Leak Detection Techniques," and 19.4 "Leak Detection Methods with Helium Leak Detectors."

[0006] EP1503199 discloses a leak detection method and a leak detection setup in which, to increase the clock frequency, one side of a molecular pump is used to supply the test gas to the gas detector in a countercurrent flow, while the other side is used solely for pumping out the gas. The fundamental aim is to achieve the highest possible sensitivity of the leak detection device; that is, figuratively speaking, as much test gas as possible should be able to flow to the detector per unit of time. Therefore, a requirement for a leak detection device of the type discussed here is the largest possible backflow of test gas through the part of the turbopump section located upstream of the test gas inlet.In normal operation, i.e. during leak detection (also referred to here as the "test mode" of the leak detection device), a relatively low compression and a relatively low pumping speed of the relevant part of the turbopump section is therefore generally advantageous with respect to the test gas, as long as it is ensured that the turbo vacuum pump can maintain the required low pressure in the detector in test mode.

[0007] At the same time, it should be noted that in practice, so-called "test gas contamination" of the detector can occur, especially with relatively large leaks in the test object. The detector must then first be evacuated, meaning the test gas must be pumped out of the detector to make it operational again for further leak detection. For this pumping process (also referred to here as the "evacuation mode" of the leak detection device), a high compression relative to the test gas and a resulting high pumping speed of the turbopump section are desirable.

[0008] Against this background, conflicting requirements exist in practice for a leak detection device and, in particular, for the turbopump section of the turbo vacuum pump. A turbopump section optimized for high pumping speed and high compression, which is advantageous in the case of test gas contamination, only allows for a comparatively low test gas backflow and thus contradicts the requirement for the highest possible test gas sensitivity of the detector during testing mode, i.e., during normal operation.

[0009] The object of the invention is therefore to create a way to enable the highest possible test gas sensitivity during normal operation and to be able to evacuate the detector as quickly as possible in the event of test gas contamination.

[0010] The solution to this problem is achieved in each case by the characteristics of the independent claims.

[0011] The leak detection device according to the invention is characterized in that at least one bypass for the test gas is provided, which leads from a bypass outlet located at the level of the test gas inlet or upstream of the test gas inlet from the turbopump section directly into the detector or to a bypass inlet located upstream of the bypass outlet into the turbopump section and which thereby bypasses at least a part of the turbopump section.

[0012] Preferably, an adjustment device is provided for changing the conductivity of the bypass relative to the test gas, wherein the adjustment device can be controlled by means of a control device of the device in order to change the conductivity between a relatively higher value and a relatively lower value depending on the operating conditions of the device.

[0013] The inventive method for leak detection is characterized in that at least one bypass is provided for a test gas originating from the test object, entering the turbo vacuum pump and flowing towards the detector in the opposite direction of pumping, which bypasses at least part of the turbo pump section and leads either directly into the detector or back into the turbo pump section.

[0014] Preferably, the conductance of the bypass relative to the test gas is changed during operation of the leak detection device from a relatively higher value for a test mode in which the test gas is detected by means of the detector to a relatively lower value for an evacuation mode in which the detector is evacuated.

[0015] The bypass allows the test gas to bypass at least part of the turbopump section. This means that at least this part of the turbopump section can be optimized for the highest possible compression and pumping speed without compromising the detector's sensitivity to the test gas during normal operation. In the event of test gas contamination, the relatively high compression and the resulting high pumping speed are advantageous because the test gas can be pumped out of the detector relatively quickly.

[0016] For this operation, also referred to herein as evacuation mode, it is possible, but not mandatory, that the conductance of the bypass is reduced, i.e., brought down to the relatively lower value.

[0017] It was found that it is possible to implement a bypass for the test gas whose conductivity relative to the test gas does not need to be reduced for evacuation mode. The conductivity of the bypass can remain unchanged without a detrimental "short-circuit effect" occurring in evacuation mode, i.e., without test gas pumped out of the detector returning to the detector to an adverse extent via the bypass. Such a passive bypass, i.e., a bypass whose conductivity relative to the test gas is not changeable or is not altered, can, for example, comprise a capillary or a selection device such as a selection membrane. A gas line in the form of such a capillary has a higher conductivity for light gases, especially helium, than for heavy gases, especially nitrogen or air.Such a selection membrane is passable for the test gas, especially helium, but not for an extraneous gas that is heavier than the test gas, especially nitrogen.

[0018] The bypass concept according to the invention thus meets the conflicting requirements for a leak detection device explained at the outset. It simultaneously achieves high test gas sensitivity of the detector during normal operation and rapid restoration of the detector's operational readiness in the event of test gas contamination.

[0019] Whether, during normal operation, the test gas flows directly into the detector via the bypass or first back into the turbopump section depends in particular on the specific design of the turbovacuum pump and / or its arrangement relative to the detector. This will be discussed in more detail elsewhere, also in connection with the exemplary embodiments shown in the drawing. If the turbovacuum pump has only an axial suction inlet for the detector, for example, a radial bypass outlet can be located between two turbopump stages, and the bypass can lead directly into the detector.If a vacuum pump is designed and arranged such that it has either several radial suction inlets or one axial suction inlet and at least one radial suction inlet for the detector, then the bypass can lead the test gas back into the turbopump section after bypassing part of the turbopump section, from where the test gas then enters the detector.

[0020] In In both cases, the turbo vacuum pump can be configured as a so-called split-flow vacuum pump. Radial suction inlets of the split-flow vacuum pump can be connected to outlets of a valve unit of the vacuum pump unit, as disclosed elsewhere, regardless of whether the split-flow vacuum pump is connected to the detector with one or more radial suction inlets or with only one axial suction inlet.

[0021] The terms "downstream" and "upstream", which are used here in particular in connection with the location of the test gas inlet, the bypass outlet and the bypass inlet as well as with the location of turbopump stages, refer, unless otherwise specified, within the scope of the present disclosure to the pumping direction of the turbo vacuum pump of the vacuum pump unit and thus to the axis of rotation of a rotor of the turbo vacuum pump.

[0022] The term "directly into the detector" refers to the fact that the bypass is not routed back into the turbopump section. This does not preclude the possibility that, in some possible embodiments, the bypass may pass through one or more further components before entering the detector, or lead into a component upstream of the detector, e.g., a chamber in the housing of the leak detection device, from where the test gas then enters the detector.

[0023] Further possible embodiments of the invention are also specified in the dependent claims, the description and the drawing.

[0024] At least two bypasses for the test gas can be provided. These bypasses can exit the turbopump section at different points and / or lead directly into the detector at different points, or initially back into the turbopump section. The sensitivity of the detector can be further increased by adding one or more additional bypasses.

[0025] The multiple bypasses can be designed in such a way that parts of the turbopump section with different compression levels and / or different suction speeds are bypassed.

[0026] Furthermore, if an adjustment device is provided, it may be stipulated that the conductance values ​​of the bypasses can be changed independently of each other.

[0027] The turbopump section preferably comprises several turbopump stages arranged sequentially in the pumping direction. Overall, the turbopump section includes a plurality of alternately arranged rotor and stator disks, which are arranged at predetermined axial distances, where "axial" refers to the axis of rotation of a rotor of the turbovacuum pump connected to the rotor disks and thus to its pumping direction. Individual turbopump stages are distinguished from one another by the fact that the axial distance between two turbopump stages is greater than the axial distance between the rotor disks or stator disks within a respective turbopump stage.

[0028] Regarding the location of the test gas inlet, it may be provided that the test gas inlet is located at the level of a turbopump stage or downstream of a turbopump stage, in particular between two turbopump stages. Alternatively, it may be provided that the test gas inlet has an axial dimension such that it not only covers the space between two turbopump stages, but also a portion of one of the two turbopump stages defining the space, or a portion of each of the two turbopump stages defining the space.

[0029] Regarding the location of the bypass outlet, it can be provided that the bypass outlet is situated at the level of a turbopump stage or downstream of a turbopump stage, particularly between two turbopump stages. It is therefore not mandatory that the bypass outlet be located at the level of an axial gap between two successive turbopump stages. The bypass outlet can also be located at the level of one of the turbopump stages. Alternatively, it can be provided that the bypass outlet has an axial dimension such that it not only covers a gap between two turbopump stages, but also a portion of one of the two turbopump stages defining the gap, or a portion of each of the two turbopump stages defining the gap.

[0030] According to some embodiments, the test gas inlet and the bypass outlet may be located axially at least substantially at the same height, particularly between two turbopump stages, so that no part of the turbopump section lies between the axial height of the test gas inlet and the axial height of the bypass outlet. The test gas thus enters the bypass without having previously flowed through any part of the turbopump section. The bypass may, in particular, comprise a capillary and / or a selection device, especially a selection membrane, as described elsewhere herein. In particular, the bypass may be passive in that no adjustment device is provided for changing the conductance of the bypass relative to the test gas, which can be achieved, for example, with a capillary or a selection device as described herein.

[0031] Regarding the location of the bypass inlet, i.e., if the bypass does not lead directly into the detector, it can be located at the level of a turbopump stage or between two turbopump stages. Alternatively, the bypass inlet can have an axial dimension such that it not only covers the space between two turbopump stages, but also a portion of one of the two turbopump stages defining the space, or a portion of each of the two turbopump stages defining the space.

[0032] Generally, the portion of the turbopump section located between the bypass outlet and the bypass inlet can be designed to achieve higher compression and / or a higher pumping speed than a portion of the turbopump section located upstream of the bypass inlet. This can be achieved by using a greater number of turbopump stages or a greater number of rotor and stator disks that work together to pump effectively. The portion of the turbopump section located between the bypass outlet and the bypass inlet is the part that is bypassed and therefore does not need to be exposed to the test gas during normal operation. At least a portion of this section of the turbopump section can be optimized for the highest possible compression and / or the highest possible pumping speed in order to evacuate the detector as quickly as possible in the event of test gas contamination during evacuation mode.

[0033] According to some embodiments, the turbo vacuum pump can be connected to the detector exclusively via an axial suction inlet, with the bypass leading directly into the detector from a bypass outlet located at the level of a turbo pump stage or between two turbo pump stages. The entire portion of the turbo pump section upstream of the bypass outlet is thus bypassed.

[0034] In In alternative embodiments, the turbo vacuum pump can be connected to the detector via several radial suction inlets spaced apart in the pumping direction, or via an axial suction inlet and one or more radial suction inlets spaced apart in the pumping direction, wherein, in particular, the bypass inlet is located at the level of a turbo pump stage or between two turbo pump stages. In this case, a portion of the turbo pump section located upstream of the bypass outlet is bypassed; that is, the test gas returns to the turbo pump section before reaching the detector.

[0035] Alternatively or additionally, in the case of a turbo vacuum pump connected to the detector via one or more radial suction inlets, the bypass can also be configured so that it does not lead back into the turbo pump section, but directly into the detector or, above the most upstream turbo pump stage, into a housing to which the detector is connected. It is also possible to have two or more bypasses, with one or more bypasses leading back into the turbo pump section and one or more other bypasses leading directly into the detector. The bypass outlets can, but need not, be at the same axial height, and the bypass outlets can, but need not, have the same circumferential position relative to the axis of rotation of a vacuum pump rotor.

[0036] Furthermore, it may be provided that a part of the turbo section located between the bypass outlet and a radial suction inlet closest to the bypass outlet is designed to achieve a higher compression and / or a higher pumping speed than any further upstream part of the turbopump section that is located either between the radial suction inlet closest to the bypass outlet and the bypass inlet or upstream of the bypass inlet.

[0037] For example, the turbo vacuum pump can have three turbopump stages upstream of the test gas inlet, with a suction inlet, a first turbopump stage, the bypass inlet, a second turbopump stage, another suction inlet, a third turbopump stage, and the test gas inlet arranged axially in succession in the direction of pumping. For example, the third and second turbopump stages can be bypassed. At least the third turbopump stage, which is located immediately upstream of the test gas inlet, can be designed to achieve higher compression and / or a higher pumping speed than the first and second turbopump stages.

[0038] This embodiment, which is also explained below using an exemplary embodiment, represents only one example of a possible design for a vacuum pump unit according to the invention. The specific design can be chosen depending on the respective requirements.

[0039] The bypass itself and its adjustment device, if present, can be designed in various ways. Numerous possibilities exist for changing the conductivity of the bypass relative to the respective test gas, if such a change in conductivity is provided for in a particular embodiment of the invention.

[0040] Generally, when providing an adjustment device, it is possible, but not mandatory, to reduce the conductivity of the bypass to zero for an evacuation mode in which the detector is to be evacuated in the event of test gas contamination. The conductivity can therefore either be reduced to zero or be greater than zero during an evacuation mode.

[0041] In some embodiments, the bypass may include at least one gas line and an adjustment device comprising at least one bypass valve controllable by the control unit. The bypass valve may, for example, be a solenoid valve. The flow cross-section of the bypass valve can be changed by means of the control unit, e.g., continuously or in stages. Alternatively, the bypass valve may be a simple switching valve that can only be switched between two positions, in particular a fully open and a fully closed position.

[0042] A rolling diaphragm, for example, can be used as an actuator for a valve of any design. Such a rolling diaphragm can also be used as an actuator for an orifice or a slide valve to change the flow cross-section of a bypass gas line.

[0043] The bypass valve can be located in the gas line, in the turbo vacuum pump, particularly on or in a pump housing, or in a valve unit associated with the turbo vacuum pump. For example, the bypass valve can be located directly at the bypass outlet from the turbo pump section. The valve unit mentioned in connection with one of these variants is a component of a leak detection device that is fundamentally known to those skilled in the art with regard to its structure and function. This valve unit, also referred to as a valve block, can be connected between the inlet for the test object to be evacuated and the test gas inlet of the turbo vacuum pump and can also be connected to a backing pump for the turbo vacuum pump. The sensitivity of the leak detection device can be adjusted using this valve unit, as is known to those skilled in the art, by tapping off a different compression of the turbo vacuum pump depending on the configuration of the individual valves in the valve unit.

[0044] In alternative embodiments, the bypass can comprise a gas line, particularly without a valve. The gas line can, in particular, be a capillary. Such a gas line has a higher conductivity for lighter gases than for heavier gases. Specifically, a gas line with a higher conductivity for helium than for nitrogen or air can be used for the bypass. According to possible further developments of the invention, in order to change the conductivity of the gas line relative to the test gas, a heating device controllable by the control unit can be provided for the gas line, the heating power of which can be varied to change the conductivity of the gas line. This allows exploitation of the fact that the conductivity of corresponding gas lines, especially capillaries, exhibits a gas-specific temperature dependency.

[0045] According to further alternative embodiments, the bypass may include a gas line, particularly without a valve, and a selection device, in particular a so-called selection membrane, which is permeable to the test gas but not to an extraneous gas that is heavier than the test gas, especially nitrogen. If such a selection device is provided, for example at the bypass outlet from the turbopump section, then the conductivity of the gas line for the test gas is relatively high. During the test mode, i.e., in normal operation, the test gas can then flow through the bypass, but not heavier gases.

[0046] The selection device can be arranged in the gas line, in the turbo vacuum pump, in particular on or in a pump housing, or in a valve unit associated with the turbo vacuum pump.

[0047] In such embodiments of the method according to the invention, in which a change in the conductivity of the bypass takes place, it is particularly provided that after evacuating the detector, the conductivity of the bypass is changed back to a relatively higher value in order to be able to operate the leak detection device again in test mode.

[0048] It is therefore fundamentally possible to operate the leak detection device permanently even in the event of intermittent test gas contamination by adjusting the conductivity of the bypass accordingly.

[0049] A tracer gas contamination in the detector can be detected by measuring the pressure within the detector. The control unit can then automatically switch from test mode to evacuation mode if the measured gas pressure inside the detector exceeds a predefined value.

[0050] In some embodiments, it may be provided that the conductance of the bypass is changed by changing the flow cross-section of a bypass valve.

[0051] In other alternative configurations, the conductivity of the bypass can be changed by heating and cooling a gas line for the test gas, in particular a capillary.

[0052] According to an unclaimed aspect, the leak detection device has a test gas channel that leads directly into the detector. "Directly into the detector" here means that no part of a pump section of a vacuum pump is subjected to test gas flow against the direction of pumping. In particular, there is no backflow of test gas.

[0053] through a turbopump section. Evacuation of the detector by means of a vacuum pump of any kind, in particular the turbo vacuum pump as disclosed herein, on the one hand, and supply of the test gas to the detector, on the other hand, then take place, so to speak, via separate flow paths. For example, the test gas can be directed from a valve unit as described herein directly to the detector. Suitable means can ensure that no foreign gases, such as nitrogen or air, enter the detector, or that only a small proportion of foreign gas, acceptable for the respective detector, enters the detector via the test gas channel. The suitable means can, for example, include a capillary and / or a selection device, such as a selection membrane, as disclosed elsewhere herein.A vacuum pump for evacuating the detector, in particular the turbo vacuum pump as disclosed herein, can then be designed without a test gas inlet or be provided with a closable test gas inlet.

[0054] The invention is described below by way of example with reference to the drawing. The drawing shows: Fig. 1 schematically shows a leak detection device according to the invention with a connected test object according to a first embodiment of the invention, in which the turbo vacuum pump is connected to the detector exclusively via an axial suction inlet, and Fig. 2 a view accordingly. Fig. 1 an alternative embodiment of the invention in which the turbo vacuum pump is connected to the detector via an axial and a radial suction inlet.

[0055] The in the Fig. 1 and 2The illustrated leak detection devices each comprise a vacuum pump unit 11 with a turbomolecular vacuum pump 15, a valve block 14, and a backing pump 39. Only the pump housing 16 and the rotating pumping components, including the rotor 41, are shown schematically for each vacuum pump 15. The differences between the two vacuum pumps 15 and their arrangement within the device are discussed in more detail below.

[0056] The turbo vacuum pump according to Fig. 1 The device is a split-flow vacuum pump and comprises an axial suction inlet 23 for connection to a detector 19, to which three turbopump stages 17a, 17b and 17c are connected in one pumping direction P. A Holweck pump stage 43 follows the last turbopump stage 17c.

[0057] In the exemplary embodiment of the Fig. 2 The turbo vacuum pump 15 is also a split-flow vacuum pump, which has an axial suction inlet 23 for connection to a detector 19 and a radial suction inlet 23 downstream of it. Between the two suction inlets 23 are a first turbo pump stage 18a and a second turbo pump stage 18b. Downstream of the radial suction inlet 23, the vacuum pump 15 has two further turbo pump stages 18c and 18d, to which a Holweck pump stage 43 is connected.

[0058] The turbo vacuum pumps 15 are each connected to the detector 19, which is also part of the leak detection device and is in the form of a mass spectrometer. In the exemplary embodiment of the Fig. 1 The detector 19 is connected to the axial suction inlet 23 via an opening 19a. In the exemplary embodiment of the Fig. 2 The detector 19 is arranged laterally with respect to the vacuum pump 15. The pump housing 16 is an outer housing into which the pump 15, together with a base housing, is inserted and with which the detector 19 is connected via openings 19a, each corresponding to one of the suction inlets 23. The vacuum pump 15 inserted into the outer housing 16 can, for example, be a so-called cartridge vacuum pump.

[0059] The leak detection devices according to Fig. 1 and Fig. 2 Each also includes a control unit 35 that controls the operation of the leak detection device.

[0060] During normal operation (test mode), the test object 13 is connected to the vacuum pump unit 11. As explained at the beginning, the test object 13 can be a component to be tested for vacuum tightness (test specimen) or a vacuum chamber in which the component to be tested is located.

[0061] For the test mode, the detector 19 and the test object 13 were evacuated to a sufficiently low vacuum pressure using the vacuum pump unit 11. If the test object has a leak, the pressure enters the test object. Fig. 1 and 2 The test gas 21, in most cases helium, illustrated by arrows, flows via the valve unit 14 to a test gas inlet 25 and thus into the turbopump section of the turbo vacuum pump 15, which is divided by the individual turbopump stages 17a to 17c ( Fig. 1 ) or 18a to 18d ( Fig. 2 ) is formed.

[0062] As mentioned elsewhere, the sensitivity of the leak detection device can be adjusted using the valve unit 14. The individual valves of the valve unit 14 are connected to ports of the turbo vacuum pump 15 spaced apart in the pumping direction P, so that, depending on the valve switching state of the valve unit 14, which is determined by the expected size of a leak in the object 13 under test, a corresponding compression of the turbo vacuum pump 15 is measured. For example, if a relatively large leak is expected, only the lowest of the three valves of the valve unit 14 is opened.

[0063] The leak detection devices each operate according to the so-called countercurrent principle, i.e., the test gas 21 enters the detector 19 against the pumping direction P in order to be detected there. According to the invention, the test gas 21 does not need to flow through the entire part of the turbopump section located upstream of the test gas inlet 25, since two bypasses 27a, 27b ( Fig. 1 ) or a bypass 28 ( Fig. 2 ) are provided, or is provided, with which, or with which, a part of the turbopump section located upstream of the test gas inlet 25 can be bypassed. The differences in this regard between the two embodiments according to the Fig. 1 and 2 This will be discussed in more detail below.

[0064] In the exemplary embodiment of the Fig. 1 Two bypasses 27a, 27b are provided for the test gas 21 flowing back through the turbopump section, whereby alternatively only a single bypass 27 may be provided or more than two bypasses 27 may be provided.

[0065] Both bypasses 27a, 27b each comprise a gas line 37 that leads directly from a bypass outlet 29 in the turbopump section to the detector 19. The bypass outlet 29 of the in Fig. 1 The bypass 27a shown on the left is located axially between the two most upstream turbopump stages 17a and 17b. The bypass outlet 29 of the in Fig. 1 The bypass 27b shown on the right lies axially at the level of the turbopump section 17a that is closest to the axial suction inlet 23.

[0066] Each of the two gas lines 37 is assigned an adjusting device 33 in the form of a bypass valve 33, which can, for example, be a solenoid valve that can be controlled by the control device 35. For example, the control device 35 can switch the valves 33 between an open state and a fully closed state.

[0067] During normal operation for detecting test gas 21 using the detector 19, the valves 33 are each open, meaning that the conductance of the gas lines 37 relative to the test gas 21 is always at the relatively higher value. The test gas 21 can then flow – as illustrated by the arrows – from the test gas inlet 25 in the counterflow direction, i.e., opposite to the pumping direction. P, flow through the turbopump section and reach the bypass outlets 29, from where the test gas 21 is then guided directly into the detector 19 via the gas lines 37. With the valves 33 open, the gas lines 37 each have a relatively high conductivity for the test gas 21, so that through the in Fig. 1 The bypass 27a shown on the left completely bypasses the first turbopump stage 17a, which is closest to the suction inlet 23, and bypasses the bypass 27a shown on the left. Fig. 1 The turbopump stage 17a is partially bypassed via bypass 27b shown on the right. This results in a significantly higher test gas flow in the detector 19 than without bypasses 27a and 27b, thus substantially increasing the sensitivity of the detector 19.

[0068] For example, if a relatively large leak in the test object 13 causes the gas pressure of the test gas 21 in the detector 19 to become too high, which can be determined by a corresponding pressure measurement in the detector 19, the bypass valves 33 are closed by means of the control device 35. This reduces the conductivity of the gas lines 37 relative to the test gas 21, allowing the turbo vacuum pump 15 to evacuate the detector 19 relatively quickly without the pumped-out test gas 21 returning to the detector 19.

[0069] The turbo vacuum pump 15 can therefore be designed with regard to pumping speed and compression such that rapid evacuation of the detector 19 is possible in the event of test gas contamination or in other situations, without these properties of the turbo vacuum pump 15 affecting the test gas sensitivity of the detector 19, since during normal operation part of the turbo pump section is bypassed due to the bypasses 27a, 27b.

[0070] In the exemplary embodiment of the Fig. 2 The bypass 28 also includes a gas line 37 in which a bypass valve 33, for example in the form of a solenoid valve, is arranged. The bypass outlet 29 is located axially at the level of the space between two turbopump stages 18c, 18d into which the test gas inlet 25 opens. The pressure level at the test gas inlet 25 can be comparatively high in certain situations, so it may be advantageous if, during normal operation, at least essentially only test gas 21 can flow through the bypass 28. The bypass 28 can then, for example, include a capillary and / or a selection device, in particular a selection membrane, as described elsewhere, to allow test gas 21 to pass through but not heavier foreign gases.

[0071] The test gas 21 can bypass the first two turbopump stages 18c and 18b, located upstream of the test gas inlet 25, via the bypass 28 and enters the turbopump section axially via the bypass inlet 31 between the first turbopump stage 18a and the second turbopump stage 18b. From there, the test gas 21 enters the detector 19, where it is detected. Alternatively, the bypass inlet 31 can also be positioned upstream of the first turbopump stage 18a. Alternatively or additionally, the first two turbopump stages 18a and 18b can also be combined into a single turbopump stage. In this respect, the Fig. 2 The illustrated design of the vacuum pump 15 and the positioning of the bypass 28 are merely examples.

[0072] The bypass 28 ensures, in particular, that the turbopump stage 18c, located immediately upstream of the test gas inlet 25 and downstream of the radial suction inlet 23 of the vacuum pump 15, can be designed with a larger number of rotor and stator disks to achieve higher compression and pumping speed than the two further upstream turbopump stages 18a and 18b. A relatively high compression and pumping speed of the turbopump stage 18c does not impair the test gas sensitivity of the detector 19, since this turbopump stage 18c is bypassed by means of the bypass 28. However, in evacuation mode, for example in the event of test gas contamination of the detector 19, it ensures that the detector can be evacuated quickly.

[0073] For an evacuation mode, the valve 33 of the bypass 28 is closed by means of the control device 35, so that in this operating mode a backflow of test gas 21 through the gas line 37 of the bypass 28 is prevented.

[0074] The embodiments described above each include an adjustment device for the bypass 28, here in the form of a valve 33. As mentioned in the introduction, in other possible embodiments of the invention no adjustment device is required for the bypass to change the conductance relative to the test gas. Bezugszeichenliste

[0075] 11 Vacuum pump unit 13 Test object 14 Valve unit 15 Turbo vacuum pump 16 Pump housing 17, 18 Turbo pump stages 19 Detector 19a Opening 21 Test gas 23 Suction inlet 25 Test gas inlet 27, 28 Bypass 29 Bypass outlet 31 Bypass inlet 33 Adjustment device, bypass valve 35 Control device 37 Gas line 39 Pre-pump 41 Rotor 43 Holweck pump stage Pump direction

Claims

1. An apparatus for leak detection according to the vacuum method using the counterflow principle, said apparatus comprising a vacuum pump unit (11) which can be connected to a test object (13) to be evacuated and which comprises a turbovacuum pump (15) comprising a turbopump section which is formed by one or more turbopump stages (17; 18), and a detector (19), in particular a mass spectrometer, for detecting a test gas (21), in particular helium, wherein the turbovacuum pump (15) is connected to the detector (19) via at least one axial and / or radial suction inlet (23) and has a test gas inlet (25) downstream of the suction inlet (23), and wherein at least a part of the turbopump section is located between the suction inlet (23) and the test gas inlet (25) in the pumping direction (P) of the turbovacuum pump (15), characterized in that at least one bypass (27, 28) is provided for the test gas (21) and leads from a bypass outlet (29), which is disposed at the level of the test gas inlet (25) or upstream of the test gas inlet (25), out of the turbopump section directly into the detector (19) or to a bypass inlet (31), which is disposed upstream of the bypass outlet (29), into the turbopump section and bypasses at least a part (17a; 18b, 18c) of the turbopump section in so doing.

2. An apparatus according to claim 1, further comprising a setting device (33) for changing the conductance of the bypass (27, 28) that is related to the test gas (21), wherein the setting device (33) can be controlled by means of a control device (35) of the apparatus to change the conductance between a relatively higher value and a relatively lower value in dependence on the operating conditions of the apparatus.

3. An apparatus according to claim 1 or 2, wherein at least two bypasses (27a, 27b) are provided for the test gas (21), and wherein the bypasses (27a, 27b) exit from the turbopump section at different positions and / or lead into the detector (19) or into the turbopump section at different positions, in particular wherein the bypasses (27a, 27b) bypass parts of the turbopump section that are configured to achieve differently high compressions and / or pumping speeds, and / or wherein the conductances of the bypasses (27a, 27b) can be varied independently of one another.

4. An apparatus according to any one of the preceding claims, wherein the turbopump section comprises a plurality of turbopump stages arranged following one another in the pumping direction (P) and the test gas inlet (25) is disposed downstream of a turbopump stage, in particular between two turbopump stages, and / or wherein the turbopump section comprises a plurality of turbopump stages arranged following one another in the pumping direction (P) and the bypass outlet (29) is disposed at the level of a turbopump stage or downstream of a turbopump stage, in particular between two turbopump stages.

5. An apparatus according to any one of the preceding claims, wherein the test gas inlet (25) and the bypass outlet (29) are disposed axially at least substantially at the same level, in particular between two turbopump stages (18c, 18d), so that no part of the turbopump section is located between the axial height of the test gas inlet (25) and the axial height of the bypass outlet (29), and / or wherein the turbopump section comprises a plurality of turbopump stages arranged following one another in the pumping direction (P) and the bypass inlet (31) is disposed at the level of a turbopump stage or between two turbopump stages.

6. An apparatus according to any one of the preceding claims, wherein the part (18b, 18c) of the turbopump section that is disposed between the bypass outlet (29) and the bypass inlet (31) is adapted to achieve a higher compression and / or a higher pumping speed than a part (18a) of the turbopump section that is disposed upstream of the bypass inlet (31).

7. An apparatus according to any one of the preceding claims, wherein the turbovacuum pump is connected to the detector (19) only via an axial suction inlet (23), and wherein the bypass (27) leads from a bypass outlet (29) directly into the detector (19), in particular wherein the bypass outlet (29) is disposed at the level of a turbopump stage (17a) or between two turbopump stages (17a, 17b) or axially covers an intermediate space between two turbopump stages and a part of at least one of the turbopump stages bounding the intermediate space.

8. An apparatus according to any one of the claims 1 to 6, wherein the turbovacuum pump (15) is connected to the detector (19) via a plurality of radial suction inlets (23) spaced apart in the pumping direction (P) or via an axial suction inlet (23) and one or more radial suction inlets (23) spaced apart in the pumping direction (P), wherein the bypass inlet (31) is disposed at the level of a turbopump stage or between two turbopump stages (18a, 18b) or axially covers an intermediate space between two turbopump stages and a part of at least one of the turbopump stages bounding the intermediate space.

9. An apparatus according to claim 8, wherein a part (18c) of the turbopump section located between the bypass outlet (29) and a radial suction inlet (23) disposed the closest upstream of the bypass outlet (29) is adapted to achieve a higher compression and / or a higher pumping speed than each part (18a, 18b) of the turbopump section that is disposed further upstream and that is disposed between the radial suction inlet (23) disposed the closest upstream of the bypass outlet (29) and the bypass inlet (31) or upstream of the bypass inlet (31).

10. An apparatus according to any one of the claims 2 to 9, wherein the bypass (27, 28) comprises at least one gas line (37) and the setting device has at least one bypass valve (33), in particular a solenoid valve, which can be controlled by means of the control device (35) and whose flow cross-section can be changed, in particular wherein the flow cross-section can be reduced to a value of zero for the evacuation mode, in particular wherein the bypass valve (33) is arranged in the gas line (37), in the turbovacuum pump (15), in particular at or in a pump housing (16), or in a valve unit (14) associated with the turbovacuum pump (15).

11. An apparatus according to any one of the claims 2 to 10, wherein the bypass (27, 28) comprises a gas line (37), in particular a capillary, without a valve, in particular wherein a setting device is provided that has a heating device for the gas line (37), which heating device can be controlled by means of the control device (35), wherein the heating power of the heating device can be changed to change the conductance of the gas line (37).

12. An apparatus according to any one of the claims 2 to 11, wherein the bypass (27, 28) comprises a gas line (37), in particular without a valve, and a selection device, in particular a selection membrane, is provided that can be passed through by the test gas, but not by a carrier gas, in particular nitrogen, which is heavier than the test gas, in particular wherein the selection device is arranged in the gas line (37), in the turbovacuum pump (15), in particular at or in a pump housing (16), or in a valve unit (14) associated with the turbovacuum pump (15).

13. A method for leak detection according to the vacuum method using the counterflow principle by means of a leak detection apparatus which comprises a vacuum pump unit (11) and a detector (19), wherein the vacuum pump unit (11) can be connected to a test object (13) to be evacuated and comprises a turbovacuum pump (15) comprising a turbopump section which is formed by one or more turbopump stages (17; 18), in particular by means of a leak detection apparatus according to any one of the preceding claims, characterized in that at least one bypass (27, 28) is provided for a test gas (21), in particular helium, which originates from the test object (13), which enters the turbovacuum pump (15) and which flows against the pumping direction (P) to the detector (19), and leads either directly into the detector (19) or back into the turbopump section while bypassing at least a part (17a; 18b, 18c) of the turbopump section.

14. A method according to claim 13, in which the conductance of the bypass (27, 28) related to the test gas (21) is changed during the operation of the leak detection apparatus from a relatively higher value for a test mode, in which the test gas (21) is detected by means of the detector (19), to a relatively lower value for an evacuation mode in which the detector (19) is evacuated, and / or wherein, after the evacuation of the detector (19), the conductance of the bypass (27, 28) is changed back to a relatively higher value again in order to operate the leak detection apparatus in the test mode again, and / or wherein a switch is made from the test mode to the evacuation mode when the gas pressure within the detector (19) exceeds a predefined value.

15. A method according to claim 13 or 14, wherein the conductance of the bypass (27, 28) is changed by changing the flow cross-section of a bypass valve (33), in particular wherein the bypass valve (33) is completely closed for the evacuation mode, and / or wherein the conductance of the bypass (27, 28) is changed by heating and cooling a gas line (37) for the test gas (21), in particular a capillary.