Device and method for leak detection

Abstract

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 for detecting a test gas, 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, 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, and wherein at least one bypass for the test gas is provided.which leads from a bypass outlet from the turbopump section located at the level of the test gas inlet or upstream of the test gas inlet directly into the detector or to a bypass inlet into the turbopump section located upstream of the bypass outlet and which thereby bypasses at least part of the turbopump section.

Description

[0001] The invention relates to a device for leak detection according to the vacuum method in the countercurrent principle, with a vacuum pump unit which can be connected to a test object to be evacuated and which comprises a turbo vacuum pump with a turbo pump section which is formed by one or more turbo pump stages, and with 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 in the pumping direction of the turbo vacuum pump, at least part of the turbo pump section is located between the suction inlet and the test gas inlet.

[0002] Furthermore, the invention relates to a method for leak detection according to 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 in the present disclosure as a shortened form of “turbomolecular...”, ie when, for example, a turbovacuum pump or a turbopump stage is mentioned, this is to be understood as a turbomolecular pump or a turbomolecular pump stage.

[0004] The concept of leak detection using the countercurrent vacuum method is well-known in vacuum technology. The test object is either the component itself to be tested, also known as the "test specimen," which requires that this component can be evacuated to a certain vacuum pressure, or the test object is a vacuum chamber into which the component to be tested is placed. In the latter case, it is not the component itself that is evacuated, but the vacuum chamber. 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 leak detectors, especially helium leak detectors, are generally known to those skilled in the art. The countercurrent principle in question here and the countercurrent leak detectors used for this purpose are also part of the specialist knowledge in the field of vacuum technology. Reference is made in particular to the relevant specialist literature in the "Wutz Handbook of Vacuum Technology (ed. Karl Jousten)" 11th edition, Springer Vieweg, and therein in particular to chapters 14.4. "Leak Detectors," 19. "Leak Detection Techniques," and 19.4. "Leak Detection Methods with Helium Leak Detectors."

[0006] DE 103 02 987 A1 discloses 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 that includes a turbo vacuum pump with a turbo pump section formed by a turbo pump stage, and a mass spectrometer for detecting test gas. The turbo vacuum pump is connected to the mass spectrometer via an axial suction inlet and has a test gas inlet downstream of the suction inlet. At least 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.

[0007] WO 95 / 04922 A1 also discloses a device for leak detection using the countercurrent vacuum method, with a high-vacuum pump that can be connected to a test object to be evacuated, and a mass spectrometer for detecting helium. The high-vacuum pump is connected to the mass spectrometer via an axial suction inlet. A bypass equipped with a membrane that preferentially permits helium is provided to bypass the entire high-vacuum pump.

[0008] EP 3 085 963 A1 discloses a high vacuum pump connected to a mass spectrometer via several radial suction inlets, wherein a flow path extending outside the pump housing and deflecting the pump flow is present between a molecular pump stage and a turbomolecular pump stage.

[0009] In principle, the leak detection device should be as sensitive as possible, i.e., figuratively speaking, as much test gas as possible should be able to flow to the detector (per unit of time). One requirement for a leak detection device of the type in question here is therefore the greatest possible test gas backflow through the part of the turbo pump section located upstream of the test gas inlet. In normal operation, i.e. during leak detection (here also referred to 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 turbo pump section in relation to the test gas are therefore generally advantageous, as long as it is ensured that the turbo vacuum pump can maintain the required low pressure in the detector in test mode.

[0010] At the same time, however, it should be noted that in practice, so-called "test gas contamination" of the detector can occur, especially in the case of relatively large leaks in the test object. The detector must then first be evacuated, i.e., the test gas must be pumped out of the detector in order to make it ready 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 the resulting high pumping speed of the turbo pump section are desirable.

[0011] Against this background, conflicting requirements exist in practice for a leak detection device, and in particular for the turbo pump section of the turbo vacuum pump. A turbo pump section optimized for high pumping speed and high compression, which is advantageous in the event of tracer gas contamination, allows only a comparatively low tracer gas backflow and thus conflicts with the requirement for the highest possible tracer gas sensitivity of the detector during test mode, i.e., during normal operation.

[0012] The object of the invention is therefore to create a possibility 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.

[0013] This problem is solved by the features of the independent claims.

[0014] The leak detection device according to the invention is characterized in that at least one bypass for the test gas is provided, which bypass leads from a bypass outlet located at the level of the test gas inlet or upstream of the test gas inlet from the turbo pump section directly into the detector or to a bypass inlet located upstream of the bypass outlet into the turbo pump section and which thereby bypasses at least part of the turbo pump section.

[0015] Preferably, an adjusting device is provided for changing the conductance of the bypass related to the test gas, wherein the adjusting device can be controlled by means of a control device of the device in order to change the conductance between a relatively higher value and a relatively lower value depending on the operating conditions of the device.

[0016] The method for leak detection according to the invention 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 to the detector against the pumping direction, which bypasses at least part of the turbo pump section and leads either directly into the detector or back into the turbo pump section.

[0017] Preferably, the conductance of the bypass related 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.

[0018] The bypass allows the test gas to bypass at least part of the turbo pump section. At least this part of the turbo pump section can therefore be optimized for the highest possible compression and pumping speed without impairing 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 have an advantageous effect in that the test gas can be pumped out of the detector relatively quickly.

[0019] 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 to the relatively lower value.

[0020] It has been found that it is possible to create a bypass for the test gas whose conductivity, related to the test gas, does not need to be reduced for the evacuation mode. The conductivity of the bypass can remain unchanged without there being a disadvantageous "short-circuit effect" in evacuation mode, i.e. without test gas pumped out of the detector passing back into the detector via the bypass to an adverse extent. Such a passive bypass, i.e. a bypass whose conductivity, related to the test gas, cannot be changed or is not changed, 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, particularly helium, than for heavy gases, particularly nitrogen or air.Such a selection membrane is passable for the test gas, in particular helium, but not for an external gas that is heavier than the test gas, in particular nitrogen.

[0021] The inventive bypass concept thus meets the conflicting requirements for a leak detection device explained above. 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.

[0022] Whether the test gas flows directly into the detector via the bypass during normal operation or first returns to the turbo pump section depends primarily on the specific design of the turbo vacuum pump and / or the arrangement of the turbo vacuum pump relative to the detector. This will be discussed in more detail elsewhere in connection with the exemplary embodiments shown in the drawings. If the turbo vacuum pump for the detector only has an axial suction inlet, a radial bypass outlet can be located between two turbo pump stages, for example, and the bypass can lead directly into the detector.If a vacuum pump is designed and arranged in such a way that it has either a plurality of radial suction inlets or an axial suction inlet and at least one radial suction inlet for the detector, then the bypass can lead the test gas, after bypassing part of the turbo pump section, back into the turbo pump section, from where the test gas then reaches the detector.

[0023] In both cases, the turbo vacuum pump can be designed 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 via one or more radial suction inlets or only via an axial suction inlet.

[0024] The terms "downstream" and "upstream", which are used here in particular in connection with the position of the test gas inlet, the bypass outlet and the bypass inlet as well as with the position of turbo pump stages, refer in the context of the present disclosure, unless otherwise stated, 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.

[0025] The term "directly into the detector" refers to the fact that the bypass is not routed back into the turbo pump section. This does not preclude the possibility that, in some possible embodiments, the bypass may pass through one or more additional devices before entering the detector, or may lead into a device upstream of the detector, e.g., a chamber in a leak detection device housing, from which the test gas then enters the detector.

[0026] Further possible embodiments of the invention are also specified in the dependent claims, the description and the drawings.

[0027] At least two bypasses can be provided for the test gas. The bypasses can exit the turbo pump section at different points and / or lead directly into the detector at different points or first back into the turbo pump section. The sensitivity of the detector can be further increased by one or more additional bypasses.

[0028] The multiple bypasses may be designed to bypass parts of the turbo pumping section with different levels of compression and / or different levels of suction speed.

[0029] Furthermore, if an adjustment device is provided, the conductance values ​​of the bypasses can be changed independently of one another.

[0030] The turbopump section preferably comprises several turbopump stages arranged successively in the pumping direction. Overall, the turbopump section comprises a plurality of alternating rotor and stator disks arranged at predetermined axial spacings, 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 defined by the fact that the axial spacing between two turbopump stages is greater than the axial spacing between the rotor disks or stator disks within a respective turbopump stage.

[0031] Regarding the location of the test gas inlet, it can be provided that the test gas inlet is located at the level of a turbo pump stage or downstream of a turbo pump stage, in particular between two turbo pump stages. Alternatively, it can be provided that the test gas inlet has an axial dimension such that the test gas inlet not only covers a gap between two turbo pump stages, but also covers a portion of one of the two turbo pump stages delimiting the gap, or a portion of each of both turbo pump stages delimiting the gap.

[0032] Regarding the location of the bypass outlet, it can be provided that the bypass outlet is located at the level of a turbo pump stage or downstream of a turbo pump stage, in particular between two turbo pump stages. It is therefore not mandatory for the bypass outlet to be located at the level of an axial gap between two consecutive turbo pump stages. The bypass outlet can also be located at the level of one of the turbo pump stages. Alternatively, it can be provided that the bypass outlet has an axial dimension such that the bypass outlet not only covers a gap between two turbo pump stages, but also covers part of one of the two turbo pump stages delimiting the gap, or part of each of both turbo pump stages delimiting the gap.

[0033] According to some embodiments, it can be provided that the test gas inlet and the bypass outlet are located axially at least substantially at the same height, in particular between two turbo pump stages, so that no part of the turbo pump section is located between the axial height of the test gas inlet and the axial height of the bypass outlet. The test gas enters the bypass without previously having flowed through part of the turbo pump section. The bypass can in particular comprise a capillary and / or a selection device, in particular a selection membrane, as described elsewhere herein. In particular, the bypass can be passive in that no adjustment device is provided for changing the conductance of the bypass related to the test gas, which can be realized, for example, with a capillary or a selection device, as described herein.

[0034] Regarding the location of the bypass inlet, i.e., in the case where the bypass does not lead directly into the detector, the bypass inlet can be located at the level of a turbo pump stage or between two turbo pump stages. Alternatively, the bypass inlet can have an axial dimension such that the bypass inlet not only covers the gap between two turbo pump stages, but also covers a portion of one of the two turbo pump stages defining the gap, or a portion of each of both turbo pump stages defining the gap.

[0035] In general, the part of the turbo pump section located between the bypass outlet and the bypass inlet can be designed to achieve higher compression and / or higher pumping speed than a part of the turbo pump section located upstream of the bypass inlet. This can be achieved by a higher number of turbo pump stages or a higher number of rotor and stator disks that interact to pump effectively. The part of the turbo pump section located between the bypass outlet and the bypass inlet is the part that is bypassed by the bypass, and therefore does not need to be flowed through by the test gas during normal operation. At least part of this part of the turbo pump section can be optimized for the highest possible compression and / or the highest possible pumping speed in order to be able to evacuate the detector as quickly as possible in an evacuation mode in the event of test gas contamination of the detector.

[0036] According to some embodiments, the turbo vacuum pump may 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 part of the turbo pump section located upstream of the bypass outlet is thus bypassed.

[0037] In alternative embodiments, the turbo vacuum pump can be connected to the detector via a plurality of 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. 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, i.e., the test gas returns to the turbo pump section before reaching the detector.

[0038] Alternatively or additionally, even with a turbo vacuum pump connected to the detector via one or more radial suction inlets, the bypass can generally be provided not to 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 provide two or more bypasses, with one or more bypasses each leading back into the turbo pump section and one or more further bypasses leading directly into the detector. The bypass outlets of the bypasses can, but do not have to, be at the same axial height, and the bypass outlets can, but do not have to, have the same circumferential position with respect to the rotational axis of a rotor of the vacuum pump.

[0039] Furthermore, it can be provided that a part of the turbo section located between the bypass outlet and a radial suction inlet located upstream of the bypass outlet is designed to achieve a higher compression and / or a higher suction capacity than any further upstream part of the turbo pump section located either between the radial suction inlet located upstream of the bypass outlet and the bypass inlet or upstream of the bypass inlet.

[0040] For example, the turbo vacuum pump can have three turbo pump stages upstream of the test gas inlet, wherein, viewed in the pumping direction, a suction inlet, a first turbo pump stage, the bypass inlet, a second turbo pump stage, another suction inlet, a third turbo pump stage, and the test gas inlet are arranged axially one after the other. For example, the third and second turbo pump stages can be bypassed by the bypass. At least the third turbo pump 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 turbo pump stage and the second turbo pump stage.

[0041] This embodiment, which is also explained below using an exemplary embodiment, represents only one example of a possible design of a vacuum pump unit according to the invention. The specific embodiment can be selected depending on the respective requirements.

[0042] The bypass itself and its adjustment device, if present, can fundamentally be designed in a variety of ways. There are numerous possibilities for changing the conductance of the bypass relative to the respective test gas, if such a change in the conductance is provided for in a particular embodiment of the invention.

[0043] Generally, when providing an adjustment device, it is possible, but not mandatory, to reduce the bypass conductance to zero for an evacuation mode in which the detector is to be evacuated in the event of test gas contamination. Thus, the conductance can either be reduced to zero or be greater than zero during an evacuation mode.

[0044] In some embodiments, it can be provided that the bypass comprises at least one gas line and an adjustment device has at least one bypass valve that can be controlled by the control device. The bypass valve can be a solenoid valve, for example. The control device can be used to change the flow cross-section of the bypass valve, e.g., continuously or in stages. Alternatively, the bypass valve can be a pure switching valve that can only be switched between two positions, in particular a fully open and a fully closed position.

[0045] 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 plate or a slide valve to change the flow cross-section of a bypass gas line.

[0046] The bypass valve 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 assigned to the turbo vacuum pump. For example, the bypass valve can be arranged 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 whose design and function are generally known to those skilled in the art. The 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 valve unit can be used to adjust the sensitivity of the leak detection device in a manner known to those skilled in the art by tapping a different compression of the turbo vacuum pump depending on the switching of the individual valves of the valve unit.

[0047] In alternative embodiments, the bypass can comprise a gas line, in particular without a valve. The gas line can in particular be a capillary. Such a gas line has a higher conductivity for light gases than for heavy gases. In particular, a gas line can be used for the bypass which has a higher conductivity for helium than for nitrogen or air. In order to change the conductivity of the gas line relative to the test gas, according to possible developments of the invention, a heating device can be provided for the gas line, the heating power of which can be changed to change the conductivity of the gas line. This makes it possible to exploit the fact that for corresponding gas lines, in particular capillaries, there is a gas-specific temperature dependence of the conductivity.

[0048] According to further alternative embodiments, the bypass may comprise a gas line, in particular without a valve, and a selection device, in particular a so-called selection membrane, through which the test gas can pass, but not an external gas that is heavier than the test gas, in particular nitrogen. If such a selection device is provided, for example, at the bypass outlet from the turbo pump section, the conductance of the gas line for the test gas is relatively high. During test mode, i.e., during normal operation, the test gas can then flow through the bypass, but not heavier gases.

[0049] 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 assigned to the turbo vacuum pump.

[0050] In those embodiments of the method according to the invention in which a conductance change of the bypass occurs, it is particularly provided that after the detector has been evacuated, the conductance of the bypass is changed back to a relatively higher value in order to be able to operate the leak detection device in test mode again.

[0051] It is therefore fundamentally possible to operate the leak detection device continuously even if test gas contamination occurs in the meantime by adjusting the conductivity of the bypass accordingly.

[0052] Test gas contamination in the detector can be detected by a corresponding pressure measurement within the detector. The control unit can then automatically switch from test mode to evacuation mode if the measured gas pressure within the detector exceeds a specified value.

[0053] 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.

[0054] In further alternative embodiments, the conductance of the bypass can be changed by heating and cooling a gas line for the test gas, in particular a capillary.

[0055] According to an unclaimed aspect, the leak detection device has a test gas channel that leads directly into the detector. In this case, “directly into the detector” means that no part of a pump section of a vacuum pump is flowed through by the test gas against the pumping direction. In particular, there is no backflow of test gas through a turbo pump section. Evacuating 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 feeding the test gas into the detector on the other hand then take place, so to speak, on separate flow paths. For example, the test gas can be fed directly to the detector from a valve unit as described herein. Suitable means can be used to ensure that no foreign gases such as nitrogen or air enter the detector.that only a small amount of foreign gas acceptable for the respective detector enters the detector via the test gas channel. Suitable means can include, for example, 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 provided with a closable test gas inlet.

[0056] The invention is described below by way of example with reference to the drawings. They show: 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 according to Fig. 1 of 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.

[0057] The Fig. 1 and Fig. The leak detection devices shown in Figure 2 each comprise a vacuum pump unit 11 with a turbomolecular vacuum pump 15, a valve block 14, and a backing pump 39. Of the vacuum pumps 15, only the pump housing 16 and the rotating pumping components including the rotor 41 are shown schematically. The differences between the two vacuum pumps 15 and their arrangement within the device will be discussed in more detail below.

[0058] The turbo vacuum pump according to Fig. 1 is a split-flow vacuum pump and comprises an axial suction inlet 23 for connection to a detector 19, to which three turbo pump stages 17a, 17b, and 17c are connected in a pumping direction P. The last turbo pump stage 17c is followed by a Holweck pump stage 43.

[0059] In the 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 thereof. 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, which are followed by a Holweck pump stage 43.

[0060] The turbo vacuum pumps 15 are each connected to the detector 19 in the form of a mass spectrometer, which is also part of the leak detection device. In the embodiment of the Fig. 1, the detector 19 is connected to the axial suction inlet 23 via an opening 19a. In the embodiment of the Fig. 2, the detector 19 is arranged laterally relative to the vacuum pump 15. The pump housing 16 here is an outer housing into which the pump 15 is inserted along with a base housing, and to which the detector 19 is connected via openings 19a associated with each 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.

[0061] The leak detection devices according to Fig. 1 and Fig. 2 each further comprises a control device 35 which controls the operation of the leak detection device.

[0062] During normal operation (test mode), the test object 13 is connected to the vacuum pump unit 11. As explained above, 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.

[0063] For the test mode, the detector 19 and the test object 13 are evacuated to a sufficiently low vacuum pressure by means of the vacuum pump unit 11. If the test object has a leak, the Fig. 1 and Fig. 2, the test gas 21, in most cases helium, illustrated by arrows, passes through the valve unit 14 to a test gas inlet 25 and thus into the turbo pump section of the turbo vacuum pump 15, which is supplied by the individual turbo pump stages 17a to 17c ( Fig. 1) or 18a to 18d ( Fig. 2) is formed.

[0064] 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 a respective compression of the turbo vacuum pump 15 is tapped 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 to be tested. For example, if a relatively large leak is expected, only the lowest of the three valves of the valve unit 14 is opened.

[0065] The leak detection devices each operate according to the so-called counterflow principle, ie the test gas 21 enters the detector 19 in the opposite direction to 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 turbo pump section located upstream of the test gas inlet 25, since two bypasses 27a, 27b ( Fig. 1) or a bypass 28 ( Fig. 2) are provided, with which a part of the turbo pump 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 Fig. 2 will be discussed in more detail below.

[0066] In the embodiment of the Fig. 1, two bypasses 27a, 27b are provided for the test gas 21 flowing back through the turbo pump section, whereby alternatively only a single bypass 27 can be provided or more than two bypasses 27 can be provided.

[0067] Both bypasses 27a, 27b each comprise a gas line 37, which leads from a bypass outlet 29 from the turbo pump section directly into the detector 19. The bypass outlet 29 of the Fig. 1 left bypass 27a is located axially between the two most upstream turbo pump stages 17a and 17b. The bypass outlet 29 of the Fig. 1 bypass 27b shown on the right is located axially at the level of the turbo pump section 17a closest to the axial suction inlet 23.

[0068] Each of the two gas lines 37 is assigned an adjusting device 33 in the form of a bypass valve 33, which can be, for example, 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.

[0069] During normal operation for detecting test gas 21 by means of detector 19, valves 33 are each open, i.e. the conductance of gas lines 37 related to test gas 21 is always at the relatively higher value. The test gas 21 can then - as illustrated by the arrows - flow from test gas inlet 25 in countercurrent direction, i.e. opposite to pumping direction P, through the turbo pump section and reach the bypass outlets 29, from where the test gas 21 is then fed via gas lines 37 directly into detector 19. When valves 33 are open, gas lines 37 each have a relatively high conductance for test gas 21, so that Fig. 1 bypass 27a shown on the left, the first turbo pump stage 17a closest to the suction inlet 23 is completely and through the Fig. 1, this turbo pump stage 17a is partially bypassed by the bypass 27b shown on the right. Overall, this results in a significantly higher test gas flow in the detector 19 than without bypasses 27a, 27b, which significantly increases the sensitivity of the detector 19.

[0070] If, for example, due to a relatively large leak in the test object 13, the gas pressure of the test gas 21 in the detector 19 becomes too high, which can be determined by a corresponding pressure measurement in the detector 19, the bypass valves 33 are closed by the control device 35. This means a reduction in the conductance of the gas lines 37 relative to the test gas 21, so that the turbo vacuum pump 15 can evacuate the detector 19 relatively quickly without the pumped-out test gas 21 being able to flow back into the detector 19.

[0071] The turbo vacuum pump 15 can therefore be designed with regard to pumping capacity and compression such that a 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 impairing the test gas sensitivity of the detector 19, since during normal operation a part of the turbo pump section is bypassed due to the bypasses 27a, 27b.

[0072] In the embodiment of the Fig. 2, the bypass 28 also comprises 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 arranged axially at the level of the intermediate space between two turbo pump 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 that it can be advantageous if, during normal operation, at least substantially only test gas 21 can flow through the bypass 28. The bypass 28 can then comprise, for example, 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.

[0073] The test gas 21 can bypass the first two turbo pump stages 18c and 18b located upstream of the test gas inlet 25 via the bypass 28 and returns axially to the turbo pump section via the bypass inlet 31 between the first turbo pump stage 18a and the second turbo pump stage 18b. From there, the test gas 21 reaches the detector 19, where it is detected. Alternatively, the bypass inlet 31 can also be positioned upstream of the first turbo pump stage 18a. Alternatively or additionally, the first two turbo pump stages 18a and 18b can also be combined into a single turbo pump stage. In this respect, the Fig. The design of the vacuum pump 15 and the positioning of the bypass 28 shown in Figure 2 are merely exemplary.

[0074] The bypass 28 particularly ensures that the turbo pump stage 18c, which is 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 a higher suction capacity than the two turbo pump stages 18a and 18b located further upstream. A relatively high compression and a relatively high suction capacity of the turbo pump stage 18c does not impair the test gas sensitivity of the detector 19, since this turbo pump stage 18c is bypassed by the bypass 28, but 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.

[0075] 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.

[0076] The embodiments explained above each comprise an adjustment device for the bypass 28, here in the form of a valve 33. As mentioned in the introductory part, in other possible embodiments of the invention, no adjustment device for the bypass is required to change the conductivity related to the test gas. List of reference symbols 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 exit 31 Bypass entry 33 Adjustment device, bypass valve 35 Control device 37 Gas pipeline 39 Backing pump 41 Rotor 43 Holweck pump stage P Pump direction

Claims

[1] Device for leak detection using the vacuum method in the countercurrent principle, with a vacuum pump unit (11) which can be connected to a test object (13) to be evacuated and which comprises a turbo vacuum pump (15) with a turbo pump section which is formed by one or more turbo pump stages (17; 18), and with a detector (19), in particular a mass spectrometer, for detecting a test gas (21), in particular helium, wherein the turbo vacuum 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 in the pumping direction (P) of the turbo vacuum pump (15) at least a part of the turbo pump section is located between the suction inlet (23) and the test gas inlet (25), characterized by , that at least one bypass (27, 28) is provided for the test gas (21), which bypass leads from a bypass outlet (29) located at the level of the test gas inlet (25) or upstream of the test gas inlet (25) from the turbo pump section directly into the detector (19) or to a bypass inlet (31) located upstream of the bypass outlet (29) into the turbo pump section and which bypasses at least a part (17a; 18b, 18c) of the turbo pump section. [2] Device according to claim 1, further comprising an adjusting device (33) for changing the conductance of the bypass (27, 28) related to the test gas (21), wherein the adjusting device (33) is controllable by means of a control device (35) of the device in order to change the conductance between a relatively higher value and a relatively lower value depending on the operating conditions of the device. [3] Device 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 the turbo pump section at different points and / or lead into the detector (19) or into the turbo pump section at different points. [4] Device according to claim 3, wherein the bypasses (27a, 27b) bypass parts of the turbo pump section which are designed to achieve different levels of compression and / or suction capacity, and / or wherein the conductances of the bypasses (27a, 27b) are independently variable. [5] Device according to one of the preceding claims, wherein the turbo pump section comprises a plurality of turbo pump stages arranged successively in the pumping direction (P) and the test gas inlet (25) is located downstream of a turbo pump stage, in particular between two turbo pump stages, and / or wherein the turbo pump section comprises a plurality of turbo pump stages arranged successively in the pumping direction (P) and the bypass outlet (29) is located at the level of a turbo pump stage or downstream of a turbo pump stage, in particular between two turbo pump stages. [6] Device according to one of the preceding claims, wherein the test gas inlet (25) and the bypass outlet (29) are located axially at least substantially at the same height, in particular between two turbo pump stages (18c, 18d), so that no part of the turbo pump section is located between the axial height of the test gas inlet (25) and the axial height of the bypass outlet (29). [7] Device according to one of the preceding claims, wherein the turbo pumping section comprises a plurality of turbo pumping stages arranged successively in the pumping direction (P) and the bypass inlet (31) is located at the level of a turbo pumping stage or between two turbo pumping stages. [8] Device according to one of the preceding claims, wherein the part (18b, 18c) of the turbo pumping section located between the bypass outlet (29) and the bypass inlet (31) is designed to achieve a higher compression and / or a higher suction capacity than a part (18a) of the turbo pumping section located upstream of the bypass inlet (31). [9] Device according to one of the preceding claims, wherein the turbo vacuum pump is connected to the detector (19) exclusively 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 located at the level of a turbo pump stage (17a) or between two turbo pump stages (17a, 17b) or axially covers an intermediate space between two turbo pump stages and a part of at least one of the turbo pump stages delimiting the intermediate space. [10] Device according to one of claims 1 to 8, wherein the turbo vacuum 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 located at the level of a turbo pumping stage or between two turbo pumping stages (18a, 18b) or axially covers an intermediate space between two turbo pumping stages and a part of at least one of the turbo pumping stages delimiting the intermediate space. [11] Device according to claim 10, wherein a part (18c) of the turbo pumping section located between the bypass outlet (29) and a radial suction inlet (23) located upstream of the bypass outlet (29) is designed to achieve a higher compression and / or a higher suction capacity than any further upstream part (18a, 18b) of the turbo pumping section located between the radial suction inlet (23) located upstream of the bypass outlet (29) and the bypass inlet (31) or upstream of the bypass inlet (31). [12] Device according to one of claims 2 to 11, wherein the bypass (27, 28) comprises at least one gas line (37) and the adjusting device has at least one bypass valve (33) which can be controlled by means of the control device (35), in particular a solenoid valve, the flow cross-section of which can be changed, in particular wherein the flow cross-section for the evacuation mode can be reduced to a value of zero. [13] Device according to claim 12, wherein the bypass valve (33) is arranged in the gas line (37), in the turbo vacuum pump (15), in particular on or in a pump housing (16), or in a valve unit (14) associated with the turbo vacuum pump (15). [14] Device according to one of claims 2 to 13, wherein the bypass (27, 28) comprises a gas line (37), in particular a capillary, without a valve, in particular wherein an adjusting device is provided which has a heating device for the gas line (37) which 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). [15] Device according to one of claims 2 to 14, 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 which is passable for the test gas, but not for a foreign gas, in particular nitrogen, which is heavier than the test gas. [16] Device according to claim 15, wherein the selection device is arranged in the gas line (37), in the turbo vacuum pump (15), in particular on or in a pump housing (16), or in a valve unit (14) associated with the turbo vacuum pump (15). [17] Method for leak detection according to the vacuum method in the countercurrent principle by means of a leak detection device 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 turbo vacuum pump (15) with a turbo pump section which is formed by one or more turbo pump stages (17; 18), in particular by means of a leak detection device according to one of the preceding claims, in which at least one bypass (27, 28) is provided for a test gas (21), in particular helium, originating from the test object (13), entering the turbo vacuum pump (15) and flowing counter to the pumping direction (P) to the detector (19), which bypasses at least a part (17a; 18b, 18c) of the turbo pump section and leads either directly into the detector (19) or back into the turbo pump section. [18] Method according to claim 17, wherein the conductance of the bypass (27, 28) related to the test gas (21) is changed during operation of the leak detection device 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. [19] Method according to claim 17 or 18, wherein after evacuating the detector (19) the conductance of the bypass (27, 28) is changed back to a relatively higher value in order to operate the leak detection device in test mode again. [20] Method according to one of claims 17 to 19, wherein the test mode is changed to the evacuation mode when the gas pressure within the detector (19) exceeds a predetermined value. [21] Method according to one of claims 17 to 20, 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. [22] Method according to one of claims 17 to 21, 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.

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