WO2022219029A1

WO2022219029A1 - Refined sniffing-based leak detection system

Info

Publication number: WO2022219029A1
Application number: PCT/EP2022/059844
Authority: WO
Inventors: Julien COULOMB; Emmanuel UROS
Original assignee: Pfeiffer Vacuum
Priority date: 2021-04-13
Filing date: 2022-04-13
Publication date: 2022-10-20
Also published as: TW202248601A; DE112022002105T5; FR3121749A1; FR3121749B1

Abstract

The invention relates to a system (1) for detecting leaks by means of a tracer gas intended to be connected to a sniffing probe to check the airtightness of an object to be tested filled with the tracer gas, comprising a first pumping device (13) making it possible to obtain a primary vacuum and comprising at least one diaphragm pump forming at least two pumping stages (E1, E2, E3, E4) connected together by a connection module (14) configured to selectively place each pumping stage (E1, E2, E3, E4) in parallel or in series with at least one other pumping stage (E1, E2, E3, E4) as a function of an operating parameter of the leak detection system (1) in order to change the mass flow rate of the gases sucked by the sniffing probe.

Description

REFINED SNIFFING-BASED LEAK DETECTION SYSTEM

TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to a system for detecting leaks to check the airtightness of an object to be tested by sniffing. The invention relates also to a pumping method of said system.

TECHNICAL BACKGROUND OF THE INVENTION

[0002] The tracer gas so-called “sniffing” test and so-called “spraying” test are known to check the airtightness of an object. These methods involve detecting the passage of the tracer gas through any leaks of the object to be tested. In “sniffing” mode, a leak detector connected to a sniffing probe is used to detect the possible presence of the tracer gas around an object to be tested filled with the tracer gas, usually pressurized. In “spraying” mode, a spray gun is used to spray the object to be tested with tracer gas, the internal volume of the object to be tested being connected to a leak detector. Helium or hydrogen is generally used as tracer gas because these gases pass through small leaks more easily than other gases, because of the small size of their molecules and their high travel velocities.

[0003] In “sniffing” mode, to lower the pressure in order to render the mass spectrometer used to measure the quantity of tracer gas functional, the leak detector comprises a pumping assembly that can be composed of a rough-vacuum pump and a turbomolecular vacuum pump mounted upstream and switched over selectively in series with the rough-vacuum pump according to the operation of the leak detector. [0004] Furthermore, it is known practice to provide several sniffing pipes connected to different points of the rough-vacuum pump to offer multiple sniffing mass flow rates capable of obtaining multiple different detection sensitivities. The vacuum pump of the leak detector is composed of two pumping stages in parallel, the downstream of which is connected to one of the sniffing pipes, these two first stages being connected to a third stage, the downstream of which is connected to another of the sniffing pipes, the third and fourth pumping stages being mounted in series in order to offer the sniffing probe multiple mass flow rates from the same diaphragm pump. One of the sniffing pipes is then chosen by the user according to the desired detection. However, this configuration requires the sniffing probe to be connected to several different points of the vacuum pump which renders the assembly much more complex.

SUMMARY OF THE INVENTION

[0005] The aim of the invention is notably to propose an affordable leak detection system for objects to be tested of widely varying volumes that allows optimized operation in “sniffing” mode, that is to say, for example, allowing a background noise that is minimized for the type of airtightness measurement desired, including a high detection sensitivity, but without notably increasing its bulk.

[0006] To this end, the invention relates to a system for detecting leaks by means of a tracer gas intended to be connected to a sniffing probe to check the airtightness of an object to be tested filled with the tracer gas, comprising a first pumping device making it possible to obtain a primary vacuum, a second pumping device making it possible to obtain a secondary vacuum, a tracer gas detection module and a processing module making it possible to manage the operation of the leak detection system, the downstream of the secondary pumping device being connected to the upstream of the primary pumping device, characterized in that the first pumping device comprises at least one diaphragm pump comprising at least two pumping stages connected together by a connection module configured to selectively place each pumping stage in parallel or in series with at least one other pumping stage as a function of at least one operating parameter of the leak detection system in order to change the mass flow rate of the gases sucked by the sniffing probe without using multiple sniffing lines.

[0007] Advantageously according to the invention, the first pumping device of the leak detection system therefore makes it possible, according to its operation, to change pumping configuration. The diaphragm pumps are selected to create the primary vacuum of the leak detector. In fact, for the application to these leak detectors, it has been observed that no other dry technology generally allows for a better trade-off between the necessary compactness, cost and performance.

[0008] The connection module of the first pumping device allows, advantageously according to the invention, a better fluidic connection between the pumping stages dependent on the use of the leak detection system. Thus, for an equivalent bulk and limited extra cost, the invention makes it possible to realize smarter pumping combining advantages that are usually difficult to combine, such as, for example, offering multiple different sensitivities in “sniffing” mode with a single detection system and by maintaining a single pipe connected between the probe and the suction input of the detection unit. It is understood that it is no longer necessary, in order to change the mass flow rate of the gases sucked by the sniffing probe, to use multiple sniffing lines or to use pumping stages with larger volumes.

[0009] The invention can also comprise one or more of the following optional features, taken alone or in combination.

[0010] The operating parameter can comprise a mass flow rate of the sucked gases measured upstream of the leak detection system, a measured temperature of the second pumping device and/or a detected tracer gas pollution (that is to say, an excessively high concentration or partial pressure of tracer gas). Preferentially, the operating parameter comprises the mass flow rate of the sucked gases measured upstream of the leak detection system, and, possibly, at least one of the other parameters cited above.

[0011] When a maximum detection sensitivity is desired, the processing module preferentially fluidically connects the first and second pumping devices and the connection module is preferentially configured so as to place all the pumping stages of the first pumping device in series in order to obtain a maximum mass flow rate of the gases sucked by the sniffing probe. The maximum mass flow rate can, for example, be substantially equal to 3000 cm³ min ¹ in standard temperature and pressure conditions. [0012] When a normal detection sensitivity is desired, the processing module preferentially fluidically connects the first and second pumping devices and the connection module is preferentially configured so as to place at least the two first pumping stages of the first pumping device in parallel in order to obtain a predetermined, so-called normal, mass flow rate of the gases sucked by the sniffing probe. The normal mass flow rate is less than the maximum mass flow rate and can, for example, lie between 200 cm³ min ¹ and 400 cm³ min ¹ in standard temperature and pressure conditions.

[0013] The first pumping device can comprise at least four pumping stages connected together by the connection module in order to enhance the background noise. It is also understood that it will be possible to go through more possible configurations, notably for intermediate sensitivity levels between that in which all the pumping stages are connected in parallel and that in which all the pumping stages are connected in series. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Other particular features and advantages of the invention will clearly emerge from the description which is given thereof hereinbelow, in an indicative and nonlimiting manner, with reference to the attached drawings, in which:

Figure 1 is a schematic view of a spraying-based leak detection system;

Figure 2 is a schematic view of a part of the leak detection system according to a “spraying” mode;

Figure 3 is a schematic view of a sniffing-based leak detection system according to the invention;

Figure 4 is a schematic view of a part of the leak detection system according to a “sniffing” mode of the invention.

DETAILED DESCRIPTION OF AT LEAST ONE EMBODIMENT OF THE INVENTION [0015] In the various figures, the elements that are identical or similar bear the same references, possibly with an added index. The description of their structure and of their function is not therefore systematically repeated.

[0016] Throughout the following, the orientations are the orientations of the figures. In particular, the terms “top”, “bottom”, “left”, “right”, “above”, “below”, “towards the front” and “toward the rear” are understood generally with respect to the direction of representation of the figures.

[0017] “Object 11 to be tested” is understood to mean any object or any installation for which it is desired to check the airtightness.

[0018] “Leak detection system 1” is understood to mean all types of devices capable of measuring leak rates, the concentration or the partial pressure of a predetermined tracer gas such as hydrogen or helium in order to identify any airtightness fault of the object 11 to be tested. These types of devices usually comprise a probe 3, a pumping module 12 (for example with a first pumping device 13 making it possible to obtain a primary vacuum, a second pumping device 15 making it possible to obtain a secondary vacuum), a tracer gas detection module 5 (for example with at least one detection element such as, for example, a mass spectrometer), a processing module 7 making it possible to manage the operation of the leak detection system 1 and, preferentially, an element 9 for displaying leak detection measurements and parameter-settings of the leak detection system 1. Usually, all the members (apart from the probe 3) of the leak detection system 1 are combined in one detection unit 4.

[0019] “First pumping device 13 making it possible to obtain a primary vacuum” is understood to mean a set of at least one pump, such as a diaphragm pump, capable of obtaining a vacuum of less or equal to 10 mbar and, typically, between 10 mbar and 10³ mbar (or between 10³ Pa and 10¹ Pa).

[0020] “Second pumping device 15 making it possible to obtain a secondary vacuum” is understood to mean a set of at least one pump, such as a turbomolecular pump capable of obtaining a vacuum of less than or equal to 10³ mbar and, typically, between 10³ mbar and 10⁸ mbar (or between 10¹ Pa and 10⁶ Pa).

[0021] “Probe 3” is understood to mean all types of devices used by a leak detection system 1 to locally examine the object to be tested. The probe 3 is therefore brought close to the object 11 to be tested by the user. According to the invention, the probe 3 is thus a sniffing probe.

[0022] In the example illustrated in Figure 1, that does not belong to the invention, the probe 3 is a spraying gun of the leak detection system 1 and has a gripping element which allows it to be manipulated by a user. The probe 3 is connected by a pipe 2a to a source 6 of tracer gas and makes it possible to release tracer gas by actuation of the control 16. The search for leaks is generally performed by moving the probe 3 to discrete points of the object 11 to be tested, notably at points likely to exhibit airtightness weaknesses, such as the seals, the welds and the couplings. Helium or hydrogen is generally used as tracer gas because these gases pass through the small leaks more easily than the other gases, because of the small size of their molecules and their high velocity.

[0023] The detection unit 4 of the leak detection system 1 comprises a suction input 10 that is intended to be connected by a line 2b to the object 11 to be tested so as to create a vacuum inside the object 11 and suck any tracer gas blown by the probe 3 which would be drawn in through a leak of the object 11 to be tested. A portion of the molecules (typically of the tracer gas) flowing counter to the gases sucked by the pumping module 12 is analysed by the gas detection module 5 using, for example, a mass spectrometer (not represented) which supplies a tracer gas leak rate to the processing module 7, preferentially for it to be able to be displayed on the display element 9. Usually, the leak rate can, for example, be measured in mbarTs ¹ or Pa m³ s ¹. A minimum tracer gas threshold is monitored by the processing module 7, the overshooting of which is considered as a leak, that is to say an airtightness fault of the object 11 to be tested.

[0024] The first pumping device 13 comprises at least one diaphragm pump comprising at least two pumping stages E1, E2, E3, E4. It is in fact understood that a diaphragm pump can combine all the pumping stages E1 , E2, E3, E4 or only a part of the pumping stages E1, E2, E3, E4, the other part of the pumping stages E1, E2, E3, E4 belonging to at least one other diaphragm pump.

[0025] In the field relating to objects to be tested of variable sizes (typically between 0.5 litre and 20 litres), that is to say for which the pumping flow rate below 10 m³ h ¹ is sufficient (in the vast majority of cases generally observed), it is preferable to use diaphragm pumps to create the primary vacuum of the leak detector. In fact, for the application to these leak detectors, no other dry technology generally allows a better trade-off between the necessary compactness, cost and performance. As an example, the roots-type vacuum pumps generally do not make it possible to obtain pumping flow rates less than 15 m³ h ¹, which makes them too bulky, too expensive and too heavy to consider using them in such leak detectors. Thus, the first pumping device 13 uses at least one diaphragm pump because it is intended to be applied to a leak detection system 1 in which the dry, that is to say without oil in the pumped flow, pumping flow rate below

10 m³ h ¹ is sufficient. [0026] The pumping stages E1, E2, E3, E4 are connected together by a connection module 14 configured to selectively place each pumping stage E1, E2, E3, E4 in parallel or in series with at least one other pumping stage E1, E2, E3, E4 as a function of an operating parameter of the leak detection system 1, such as, typically, at the suction input 10.

[0027] The connection module 14 preferentially comprises ducts C5, C6, C7, C8, C9, C10, C11, C12, C13, C14, C15, C16, C17 connecting the input and the output of each pumping stage E1, E2, E3, E4 of the first pumping device 13 and closure elements V1, V2, V3, V4, V5, V6, V7, V8, V9, V10, V11 selectively allowing passage in the ducts C6, C7, C8, C9, C10, C11, C13, C14, C15, C16, C17. The closure elements V1, V2, V3, V4, V5, V6, V7, V8, V9, V10, V11 can be valves that can notably be driven by the processing module 7 and/or check valves each configured to allow opening/closure according to a predetermined pressure threshold in order to modify the connections between the pumping stages E1, E2, E3, E4, preferentially as a function of the pressure upstream of the leak detection system 1 and/or as a function of the pressure upstream or downstream of a pumping stage E1 , E2, E3, E4. Each pressure can be monitored by a dedicated pressure sensor, such as the sensor 18 for example, to monitor the pressure upstream of the leak detection system 1.

[0028] The first pumping device 13 of the leak detection system 1 therefore makes it possible, depending on its operation, to change pumping configuration, notably according to whether it is in preliminary suction phase of the object 11 to be tested or in phase of checking the airtightness of the object 11 to be tested. The connection module 14 of the first pumping device 13 therefore allows a better fluidic connection between the pumping stages E1, E2, E3, E4 according to the use of the leak detection system 1. Thus, for equivalent bulk and limited extra cost, it is possible to produce smarter pumping combining advantages that are usually impossible to combine, such as, for example, maximal shortening of the duration of the preliminary suction phase and maximal reduction of the background noise (very low limit vacuum pressure) of the phase of checking of the airtightness of the object 11 to be tested with respect to the number of pumping stages E1, E2, E3, E4 without having to use multiple types of first primary pumping device or without using pumping stages with larger volumes.

[0029] That is made possible because, when the pressure upstream of the leak detection system 1 is substantially equal to atmospheric pressure, that is to say at the start of the suction of the object 11 to be tested, the processing module 7 disconnects the second pumping device 15 and the connection module 14 is configured so as to place all the pumping stages E1, E2, E3, E4 of the first pumping device 13 in parallel in order to maximize the pumping flow rate inside the object 11 by the first pumping device 13. Furthermore, when the pressure upstream of the leak detection system 1 is below a minimum pressure threshold (preferably lying between 1 mbar and 10 mbar) allowing the detection module 5 to operate in high sensitivity mode, the processing module 7 connects, that is to say fluidically connects, the first and second pumping devices 13, 15 in series and the connection module 14 is configured so as to connect all the pumping stages E1, E2, E3, E4 of the first pumping device 13 in series to lower to the lowest possible level the pressure inside the object 11 and thus maximally enhance the sensitivity of the detection module 5.

[0030] Furthermore, when all the pumping stages of the first pumping device are in parallel and preferably throughout the preliminary suction of the object 11 to be tested, the processing module 7 imposes a speed of rotation for each pump, that is to say one or more diaphragm pumps used, greater than its nominal speed of rotation in order to maximize the pumping flow rate of the first pumping device 13. The imposed speed of rotation can for example lie between 100% and 170% of its nominal speed whereas, in the other configurations outside of preliminary suction, the normal speed of each pump could be limited between 30% and 100% of its nominal speed (apart from exceptions as explained hereinbelow).

[0031] In an intermediate mode of operation, such as, for example, when the pressure upstream of the leak detection system 1 is below a maximum pressure threshold (preferentially between 15 mbar and 50 mbar) from which the detection module 5 can operate, the processing module 7 connects, that is to say fluidically connects, the first and second pumping devices 13, 15 and the connection module 14 is configured so as to connect at least the two last pumping stages E1, E2, E3, E4 of the first pumping device in series in order to guarantee a sufficient sensitivity of the detection module 5 in order, for example, to begin to check the airtightness of the object 11 to be tested.

[0032] The first pumping device 13 comprises at least two pumping stages E1, E2, E3, E4, that is to say that it can, for example, comprise two, three, four, five or six pumping stages E1, E2, E3, E4. In the example illustrated in Figure 2, the first pumping device 13 comprises a single diaphragm pump with four pumping stages E1, E2, E3, E4. Obviously, the more pumping stages E1, E2, E3, E4 there are, the more it will be possible to improve the pumping flow rate and the limit vacuum pressure of the first pumping device 13. It is also understood that it will be possible to go through more possible configurations between that in which all the pumping stages are connected in parallel on startup and that in which all the pumping stages are connected in series in the event of a need for a high-sensitivity detection.

[0033] The example illustrated in Figure 2 will now be explained in order to describe an example of optimized operation with four pumping stages E1, E2, E3, E4. In this example, the first pumping device 13 comprises a connection module 14 with ducts C5, C6, C7, C8, C9, C10, C11, C12, C13, C14, C15, C16, C17 connecting the suction input 10 by the duct C1. Closure elements V1, V2, V3, V4, V5, V6, V7, V8, V9, V10, V11 selectively allow passage in, respectively, ducts C6, C7, C8, C9, C10, C11, C14, C16, C13, C15, C17. In this particular example, the closure elements V7 and V8 are controllable valves because following the reduction pressure they are intended to be successively closed, open and then once again closed. The other elements V1, V2, V3, V4, V5, V6, V9, V10, V11 can without preference be controllable valves and/or check valves each configured according to a predetermined pressure threshold upstream of the leak detection system 1 and/or upstream and downstream of a pumping stage E1, E2, E3, E4. The first pumping device 13 is configured to discharge the gases through the discharge output 17, preferentially at ambient pressure.

[0034] In the example of Figure 2, the second pumping device 15 comprises a turbomolecular vacuum pump T, the upstream (suction) of which is connected to the detection module 5 and which can be connected downstream (discharge and intermediate stages) at three different levels of the turbomolecular vacuum pump T to the duct C1 by, respectively, the ducts C2, C3, C4, so as to be able to adapt the withdrawal flow to the level of the leaks. The passage of these latter ducts C2, C3, C4 is selectively controlled by the closure elements V12, V13, V14 which are, preferentially, controllable valves. Finally, the passage element V15 which, preferably, is a controllable valve, is intended to close the duct C1 between its connections with the ducts C3 and C4.

[0035] The following table presents an example of management of the leak detection system 1.

[0036] In a first phase of rough suction, the closure elements V1, V 2, V3, V 4, V5, V6,

V15 allow passage in, respectively, the ducts C6, C7, C8, C9, C10, C11, C1 in addition to the ducts C5 and C12 which are permanently open. The second pumping device 15 is therefore isolated. The connection module 14 is configured so as to place all the pumping stages E1, E2, E3, E4 of the first pumping device 13 in parallel in order to maximize the pumping flow rate inside the object 11 by the first pumping device 13 until a predetermined pressure threshold P1 is reached upstream of the leak detection system 1. The pressure threshold P1 lies, preferentially, between 100 mbar and 400 m bar, that is to say, for example, equal to 100 mbar, 125 mbar, 150 mbar, 175 mbar, 200 mbar, 225 mbar, 250 mbar, 275 mbar, 300 mbar, 325 mbar, 350 mbar, 375 mbar, 300 mbar, 325 mbar, 350 mbar, 375 mbar or 400 mbar.

[0037] Below the pressure threshold P1, a second phase of fine suction is begun in which the closure elements V1, V6, V7, V8, V10, V15 allow passage in, respectively, the ducts C6, C11, C14, C16, C15, C1 in addition to the ducts C5 and C12 which are permanently open. The second pumping device 15 is therefore still isolated. The connection module 14 is configured so as to place the pumping stages E1 and E2 in parallel then connected downstream by the ducts C14, C15, C16 to the pumping stages E3 and E4, also in parallel, in order to reduce the pumping flow rate but enhance the limit vacuum pressure until a predetermined pressure threshold P2 is reached upstream of the leak detection system 1. The maximum pressure threshold P2 lies, preferentially, between 15 mbar and 50 mbar, that is to say, for example, equal to 15 mbar, 16 mbar,

17 mbar, 18 mbar, 19 mbar, 20 mbar, 21 mbar, 22 mbar, 23 mbar, 24 mbar, 25 mbar,

26 mbar, 27 mbar, 28 mbar, 29 mbar, 30 mbar, 31 mbar, 32 mbar, 33 mbar, 34 mbar,

35 mbar, 36 mbar, 37 mbar, 38 mbar, 39 mbar, 40 mbar, 41 mbar, 42 mbar, 43 mbar,

44 mbar, 45 mbar, 46 mbar, 47 mbar, 48 mbar, 49 mbar or 50 mbar.

[0038] Below the maximum pressure threshold P2, a third phase of measurement of major leaks can be begun. In the third phase, the closure elements V1, V7, V10, V11, V14, V15 allow passage in, respectively, the ducts C6, C14, C15, C17, C4, C1 in addition to the ducts C5 and C12 which are permanently open. The second pumping device 15 is connected to the first pumping device 13. The connection module 14 is configured so as to place the pumping stages E1 and E2 in parallel then connected downstream by the ducts C14, C15, to the pumping stages E3 and E4 that are now in series in order to reduce the pumping flow rate but enhance the limit vacuum pressure until a predetermined minimum pressure threshold P4 is reached upstream of the leak detection system 1. The minimum pressure threshold P4 lies, preferentially, between 1 mbar and 10 mbar, that is to say equal to 1 mbar, 2 mbar, 3 mbar, 4 mbar, 5 mbar, 6 mbar, 7 mbar, 8 mbar, 9 mbar or 10 mbar.

[0039] According to a particular operation, notably according to the pressure range P3 upstream of the leak detection system 1 and the specific demands of the user, the second device 15 can have different modes of operation. As a nonlimiting example, in a pressure range P3 lying between 2 mbar and 5 mbar, a fourth phase of average leak measurement can be begun without necessarily changing the configuration of the connection module 14 of the first pumping device 13, that is to say by keeping the closure elements V1, V7, V10, V11 open in, respectively, the ducts C6, C14, C15, C17, in addition to the ducts C5 and C12 which are permanently open. The closure elements V13, V14, V15, on the other hand, allow passage in, respectively, the ducts C3, C4, C1 in order to render the detection module 5 of the leak detection system 1 more sensitive, notably by allowing the counter-flow of a part of the molecules (typically of the tracer gas) to enter at an intermediate level (duct C3) of the turbomolecular vacuum pump T in addition to the connection with the discharge duct C4 of the turbomolecular vacuum pump T.

[0040] Below the minimum pressure threshold P4, a fifth phase of measurement of small leaks can be begun. In the fourth phase, the closure elements V9, V10, V11, V12, V14 allow passage in, respectively, the ducts C14, C13, C15, C17, C2, C4 in addition to the ducts C5 and C12 which are permanently open. The second pumping device 15 is still connected to the first pumping device 13 but the flow from the suction input 10 is forced to enter into the second pumping device 15 before being discharged in the first pumping device 13 before being discharged by the discharge output 17. The connection module 14 is configured so as to place all the pumping stages E1, E2, E3, E4 in series to lower the pressure to the lowest possible level inside the object 11 and thus enhance to the maximum the sensitivity of the detection module 5. The minimum pressure threshold P4 is, preferentially, less than 1 mbar.

[0041] It is also possible to determine the pressure variations upstream of the detection system 1 indirectly, that is to say based on a datum making it possible to estimate the pressure variation. Thus, as a variant, it is also possible to monitor the flow and the flow rate of the detection system 1. In fact, the formula: pressure = mass flow rate/volume flow rate allows indirect measurement.

[0042] As explained above, the operating parameter should not be limited to the pressure measured, for example by the sensor 18, upstream of the leak detection system 1, and could, possibly, also take account of a measured temperature of the second pumping device 15 and/or a detected tracer gas pollution and/or a detection of condensable gas and/or a state of operation of a bleed to order the change of configuration by the connection module 14.

[0043] In fact, if the pressure downstream of the turbomolecular pump T (duct C4) is too high, the turbomolecular pump T can rise in temperature. This increase in temperature may lead to the activation of its safety mode, that is to say that the operation of the turbomolecular pump T is slowed down or stopped to avoid any damage. Thus, based on monitoring by the processing module 7 of a temperature threshold of the turbomolecular pump T, if the temperature exceeds the threshold, the connection module 14 can be used to demand all the pumping stages E1, E2, E3, E4 to be in series, temporarily (timer) and/or until the temperature of the turbomolecular pump T drops back below the same threshold or a lower threshold than that which triggered the change of configuration. In fact, that would make it possible to lower the pressure in the duct C4 using the first pumping device 13 to avoid activation of its safety mode. Each temperature threshold could, for example, lie between 40°C and 70°C, that is to say for example be equal to 40°C, 45°C, 50°C, 55°C, 60°C, 65°C or 70°C.

[0044] It is also possible to determine the temperature variations of the turbomolecular pump T indirectly, that is to say based on a datum making it possible to estimate the temperature variation. Thus, as a variant, it is also possible to monitor the power consumed by the turbomolecular pump T or the value of the current powering the turbomolecular pump T.

[0045] Furthermore, if the pumping module 12 is saturated with tracer gas, typically when a maximum tracer gas threshold measured by the detection module 5 is exceeded, it is considered that there is tracer gas pollution in the leak detection system 1. The latter can therefore no longer correctly check the leaks of the object 11 to be tested. Thus, from the monitoring by the processing module 7 of a maximum tracer gas threshold, if the maximum threshold is exceeded, the connection module 14 can be used to demand at least the two first pumping stages E1, E2, E3, E4 to be in parallel, temporarily (timer) and/or until the tracer gas pollution in the leak detection system 1 is considered to be ended. In fact, that would make it possible to increase the flow rate downstream of the turbomolecular pump T using the first pumping device 13 to discharge the excess tracer gas. The maximum threshold to consider a trace gas pollution in the leak detection system 1 could, for example, be equal to 10⁴ mbarTs ¹. [0046] This stage of depollution, referred to as active recovery, can be enhanced by imposing a speed of rotation for each pump, that is to say one or more diaphragm pumps used, that is greater than its nominal rotation speed in order to maximize the pumping flow rate of the first pumping device 13. The imposed rotation speed can, for example, lie between 100% and 170% of its nominal speed.

[0047] The presence of condensable gas in the pumping module 12 can also be taken into account. In fact, such condensable gases, such as, for example, steam, can make the pumping difficult. Consequently, using a dedicated sensor (not represented) in the pumping module 12, the presence of such condensable gases is monitored by the processing module 7. Thus, in the affirmative, the connection module 14 can be used to demand all the pumping stages E1, E2, E3, E4 to be in series, temporarily (timer) and/or until the presence of condensable gases in the leak detection system 1 is considered to be ended. In fact, that would make it possible to lower the pressure in the pumping module 12 to discharge any condensable gas. The maximum threshold for considering a tracer gas pollution in the leak detection system 1 could, for example, be equal to

10⁴ mbarTs ¹.

[0048] Finally, it is commonplace, for the “suction” mode, for there to be a bleed in the pumping module 12 to assist in the discharging of the accumulation of tracer gas in the pumping stages E1, E2, E3, E4. In fact, if the vacuum is high, reducing the proportion of air with respect to the tracer gas renders the pumping of the tracer gas which remains stored in the pumping stages E1, E2, E3, E4 more difficult. The bleed therefore makes it possible to create a temporary flow capable of driving the excess tracer gas to the discharge output 17. Consequently, according to the state of operation of the bleed, the connection module 14 can be used to modify the configuration of the pumping stages E1 , E2, E3, E4, temporarily (timer) and/or until a new change of state of operation of the bleed (opening to closure, closure to opening, variations of the quantity of opening, etc.).

[0049] In the example illustrated in Figure 3, the probe 3 is a sniffing probe and has a gripping element allowing it to be manipulated by the user. The probe 3 is connected by a flexible pipe 2 to a suction input 10 of the detection unit 4 so as to suck the gases surrounding the object 11 to be tested filled with tracer gas. As for the “spraying” mode, helium or hydrogen is generally used as tracer gas in “sniffing” mode, because these gases pass through the small leaks more easily than the other gases, because of the small size of their molecules and their high velocity.

[0050] A part of the molecules (typically of the tracer gas) sucked by the pumping module 12 is analysed by the gas detection module 5 using, for example, a mass spectrometer (not represented) which supplies a tracer gas leak rate to the processing module 7 for it to be preferentially able to be displayed on the display element 9. Usually, the leak rate can, for example, be measured in mbarTs ¹ or Pa m³ s ¹. A minimum tracer gas threshold is monitored by the processing module 7, any overshoot of which is considered to be a leak, that is to say an airtightness defect of the object 11 to be tested.

[0051] Advantageously according to the invention, the pumping module 12 in “sniffing” mode can comprise an architecture illustrated in the example of Figure 4. Thus, advantageously according to the invention, the pumping stages E1, E2, E3, E4 are connected together by a connection module 14 configured to selectively place at least one pumping stage E1, E2, E3, E4 in parallel or in series with at least one other pumping stage E1, E2, E3, E4 as a function of an operating parameter of the leak detection system 1. Typically, for a first pumping device 13 with two pumping stages E1, E2, one or two diaphragm pumps can be used without departing from the scope of the invention.

[0052] In “sniffing” mode, the logic is different compared to that in “spraying” mode. In fact, in “sniffing” mode, it is no longer the vacuum pressure which is primarily monitored but the mass flow rate of the sucked gases measured upstream of the leak detection system 1, typically using the sensor 19. Such a mass flow rate is measured in cm³· min ¹ in standard temperature and pressure conditions (known by the acronym “seem” derived from the expression “standard cubic centimetre per minute”).

[0053] Thus, the higher the mass flow rate becomes, the more the detection module 5 will be statistically capable of detecting a leak of the object 11 over a greater extent around the probe 3. In fact, with a higher flow rate, the depression generated at the free end of the probe 3 will be capable of sucking more gas mixture per the same unit of time and therefore creating a more extended suction flow around the probe 3. It is understood that, from a certain point of view, a higher flow rate allows a better sensitivity, that is to say detecting a leak at a greater distance, compared to a lower flow rate of the same detection system 1.

[0054] In “sniffing” mode, that is to say when the leak detection system 1 is intended to be connected to the probe 3, the operating parameter can thus comprise the mass flow rate of the sucked gases measured upstream of the leak detection system 1 and, possibly, a measured temperature of the second pumping device and/or a detected tracer gas pollution.

[0055] The connection module 14 preferentially comprises ducts C5, C6, C12, C13, C14, C15, C17 connecting the input and the output of each pumping stage E1 , E2, E3, E4 of the first pumping device 13 and closure elements V1 , V7, V9 allowing, respectively, passage in the ducts C6, C14, C13. The closure elements V1 , V7, V9 can be valves that can be controlled notably by the processing module 7 and/or check valves each configured to allow opening/closure according to a predetermined pressure threshold in order to modify the connections between the pumping stages E1, E2, E3, E4 as a function of the desired mass flow rate. The real flow rate can be monitored by a dedicated flow rate sensor such as, for example, the sensor 19 situated on the duct C18 immediately downstream of the suction input 10.

[0056] Advantageously according to the invention, the first pumping device 13 of the leak detection system 1 therefore makes it possible, depending on its operation, to change pumping configuration notably according to whether it is in phase of checking of the object 11 to be tested in normal sensitivity mode or maximum sensitivity mode. The connection module 14 of the first pumping device 13 therefore allows a better fluidic connection between the pumping stages E1, E2, E3, E4 based on the use of the leak detection system 1.

[0057] Thus, for an equivalent bulk and a limited extra cost, the invention makes it possible to produce smarter pumping combining advantages that are usually impossible to combine such as, for example, offering multiple different sensitivities in “sniffing” mode with a single detection system 1 while keeping a single pipe 2 connected between the probe 3 and the suction input 10 of the detection unit 4.

[0058] That is made possible because, when a maximum detection sensitivity is desired, the processing module 7 preferentially fluidically connects the first and second pumping devices 13, 15 and the connection module 14 is preferentially configured so as to place all of the pumping stages E1, E2, E3, E4 of the first pumping device 13 in series in order to obtain a first mass flow rate of the gases sucked by the probe 3. The first predetermined mass flow rate can for example be substantially equal to 3000 cm³· min ¹ in standard temperature and pressure conditions.

[0059] On the other hand, when a normal detection sensitivity is desired, the processing module 7 preferentially fluidically connects the first and second pumping devices 13, 15 and the connection module 14 is preferentially configured so as to place at least the two first pumping stages E1, E2 of the first pumping device 13 in parallel in order to obtain a second predetermined mass flow rate of the gases sucked by the probe 3. The second predetermined mass flow rate can for example lie between 200 cm³ min ¹ and 400 cm³ min ¹ in standard temperature and pressure conditions.

[0060] According to the invention, the first pumping device 13 comprises at least two pumping stages E1 , E2, E3, E4, that is to say can, for example, comprise two, three, four, five or six pumping stages E1, E2, E3, E4 without departing from the scope of the invention. In the example illustrated in Figure 4, the first pumping device 13 comprises a single diaphragm pump with four pumping stages E1, E2, E3, E4. Obviously, the more pumping stages E1, E2, E3, E4 there are, the more it will be possible to improve the pumping flow rate and the limit vacuum pressure of the first pumping device 13. It is also understood that it will be possible to go through more possible configurations between that in which all the pumping stages are connected in parallel and that in which all the pumping stages are connected in series.

[0061] The example illustrated in figure 4 will now be explained in order to describe an example of optimized operation with four pumping stages E1, E2, E3, E4. In this example, the first pumping device 13 comprises a connection module 14 with ducts C5, C6, C12, C13, C14, C15, C17 connecting the suction input 10 by the duct C18. Closure elements V1, V7, V 9 selectively allow passage in, respectively, the ducts C6, C14, C13. The first pumping device 13 is configured to discharge the gases by the discharge output 17 preferentially at an ambient pressure.

[0062] In the example of Figure 4, the second pumping device 15 comprises a turbomolecular vacuum pump T of which the upstream (suction) is connected to the detection module 5 and which can be connected downstream (discharge and intermediate stage) at two different levels of the turbomolecular vacuum pump T to the duct C5 and C18 by, respectively, the ducts C4 and C19. The passage of the ducts C4, C19 is selectively controlled by the closure elements V14, V 17 which are, preferentially, controllable valves. Finally, provision is made for the duct C18 to be connected, via the closure element V16, to the duct C15 between the downstream of the pumping stage E2 and the upstream of the pumping stage E3.

[0063] The following table presents an example of management of the leak detection system 1.

[0064] Above the mass flow rate threshold D1 and typically at the first mass flow rate

Dmax, a phase of high-sensitivity measurement can be begun. In this phase, the closure elements V9, V14, V16, V 17 allow passage in, respectively, the ducts C13, C4, C18, C19 in addition to the ducts C5, C12, C15 and C17 which are permanently open. The second pumping device 15 is connected to the first pumping device 13. The connection module 14 is configured so as to place the pumping stages E1 and E2 in series then connected downstream, by the duct C15, to the pumping stages E3 and E4 in series in order to obtain a first mass flow rate of the gases sucked by the probe 3. According to the invention, the mass flow rate threshold D1 lies, preferentially, between 200 cm³ min ¹ and 400 cm³ min ¹ in standard temperature and pressure conditions, that is to say is for example equal to 200 cm³ min ¹, 225 cm³ min ¹, 250 cm³ min ¹, 275 cm³ min ¹, 300 cm³ min ¹, 325 cm³ min ¹, 350 cm³ min ¹, 375 cm³ min ¹ and 400 cm³ min ¹. Typically, in the configuration explained above and in the absence of obstructions present in the probe 3, the first mass flow rate Dmax is reached and is preferentially equal to 3000 cm³· min ¹ in standard temperature and pressure conditions. [0065] Below the mass flow rate threshold D1 and typically at the second mass flow rate Dmin, a phase of measurement at normal sensitivity can be begun. In this phase, the closure elements V1, Ml, V 14, V16, V 17 allow passage in, respectively, the ducts C6, C14, C4, C18, C19 in addition to the ducts C5, C12, C15 and C17 which are permanently open. The second pumping device 15 is connected to the first pumping device 13. The connection module 14 is configured so as to place the pumping stages E1 and E2 in parallel then connected downstream, by the duct C15, to the pumping stages E3 and E4 in series in order to obtain a second mass flow rate of the gases sucked by the probe 3. According to the invention, the mass flow rate threshold D1 lies, preferentially, between 200 cm³· min ¹ and 400 cm³· min ¹ in standard temperature and pressure conditions, that is to say can for example be equal to 200 cm³ min ¹, 225 cm³ min ¹, 250 cm³ min ¹, 275 cm³ min ¹, 300 cm³ min ¹, 325 cm³ min ¹, 350 cm³ min ¹, 375 cm³ min ¹ and 400 cm³ min ¹. Typically, in the configuration explained above and in the absence of obstructions present in the probe 3, the second mass flow rate Dmin is reached and is preferentially equal to 300 cm³· min ¹ in standard temperature and pressure conditions.

[0066] It is also possible to determine mass flow rate variations upstream of the detection system 1 indirectly, that is to say from a datum making it possible to estimate the mass flow rate variation. Thus, as a variant, it is also possible to monitor the pressure and the volume flow rate of the detection system 1. In fact, the formula: mass flow rate = pressure * volume flow rate allows indirect measurement without departing from the scope of the invention.

[0067] As explained above, the operating parameter should not be limited to the mass flow rate measured, for example by the sensor 19, upstream of the leak detection system 1 and could, possibly, also take account of a measured temperature of the second pumping device 15 and/or a detected tracer gas pollution to order the change of configuration by the connection module 14.

[0068] In fact, if the pressure downstream of the turbomolecular pump T (duct C4) is too high, the turbomolecular pump T may rise in temperature. This increase in temperature can lead to the activation of its safety mode, that is to say that the operation of the turbomolecular pump T is slowed down or stopped to avoid any damage. Thus, based on the monitoring by the processing module 7 of a temperature threshold of the turbomolecular pump T, if the temperature exceeds the threshold, the invention would advantageously make it possible to use the connection module 14 to demand all the pumping stages E1, E2, E3, E4 to be in series, temporarily (timer) and/or until the temperature of the turbomolecular pump T drops down below the same threshold or a lower threshold than that which triggered the change of configuration. In fact, that would make it possible to lower the pressure in the duct C4 using the first pumping device 13 to avoid activation of its safety mode. Each temperature threshold could, for example, lie between 40°C and 70°C, that is to say for example be equal to 40°C, 45°C, 50°C, 55°C, 60°C, 65°C or 70°C.

[0069] It is also possible to determine the temperature variations of the turbomolecular pump T indirectly, that is to say based on a datum making it possible to estimate the temperature variation. Thus, as a variant, it is also possible to monitor the power consumed by the turbomolecular pump T or the value of the current powering the turbomolecular pump T without departing from the scope of the invention.

[0070] Furthermore, if the pumping module 12 is saturated with tracer gas, typically when a maximum tracer gas threshold measured by the detection module 5 is exceeded, it is considered that there is tracer gas pollution in the leak detection system 1. The latter can therefore no longer correctly check the leaks of the object 11 to be tested. Thus, based on monitoring by the processing module 7 of a maximum tracer gas threshold, if the maximum threshold is exceeded, the invention would advantageously make it possible to use the connection module 14 to demand at least the two first pumping stages E1, E2 to be in parallel, temporarily (timer) and/or until the tracer gas pollution in the leak detection system 1 is considered to be ended. In fact, that would make it possible to increase the flow rate downstream of the turbomolecular pump T using the first pumping device 13 to discharge the excess tracer gas. The maximum threshold to consider a tracer gas pollution in the leak detection system 1 could, for example, be equal to

10⁴ mbarTs ¹.

[0071] This depollution phase, called active recovery, can be enhanced by imposing a speed of rotation for each pump, that is to say one or more diaphragm pumps used, greater than its nominal speed of rotation in order to maximize the pumping flow rate of the first pumping device 13. The imposed speed of rotation can for example lie between 100% and 170% of its nominal speed, while, for the rest of the time, the normal speed of each pump could be limited between 30% and 100% of its speed.

[0072] The invention is not limited to the embodiments and variants presented and other embodiments and variants will be clearly apparent to the person skilled in the art. Thus, the embodiments and variants can be combined with one another without departing from the scope of the invention. In a nonlimiting manner, it is possible to envisage the first pumping device 13 comprising more than four pumping stages E1, E2, E3, E4 to further enhance the pumping flow rate and the limit vacuum pressure. The connection module 14 will then be adapted by increasing the number of ducts and valves.

Claims

1. System (1) for detecting leaks by means of a tracer gas intended to be connected to a sniffing probe (3) to check the airtightness of an object (11) to be tested filled with the tracer gas, comprising a first pumping device (13) making it possible to obtain a primary vacuum, a second pumping device (15) making it possible to obtain a secondary vacuum, a tracer gas detection module (5) and a processing module (7) making it possible to manage the operation of the leak detection system (1), the downstream (C4) of the secondary pumping device (15) being connected to the upstream (C5) of the primary pumping device (13), characterized in that the first pumping device (13) comprises at least one diaphragm pump comprising at least two pumping stages (E1, E2, E3, E4) connected together by a connecting module (14) configured to selectively place each pumping stage (E1, E2, E3, E4) in parallel or in series with at least one other pumping stage (E1, E2, E3, E4) as a function of at least one operating parameter of the leak detection system (1) in order to change the mass flow rate of the gases sucked by the sniffing probe (3) without using multiple sniffing lines.

2. Leak detection system (1) according to the preceding claim, wherein the operating parameter comprises a mass flow rate of the sucked gases measured upstream of the leak detection system (1), a measured temperature of the second pumping device (15) and/or a detected tracer gas pollution.

3. Leak detection system (1) according to the preceding claim, wherein, when a maximum detection sensitivity is desired, the processing module (7) fluidically connects the first and second pumping devices (13, 15) and the connection module (14) is configured so as to place all the pumping stages (E1, E2, E3, E4) of the first pumping device (13) in series in order to obtain a maximum mass flow rate of the gases sucked by the sniffing probe (3).

4. Leak detection system (1) according to the preceding claim, wherein the maximum mass flow rate is substantially equal to 3000 cm³ min ¹ in standard temperature and pressure conditions.

5. Leak detection system (1) according to any one of the preceding claims, wherein, when a normal detection sensitivity is desired, the processing module (7) fluidically connects the first and second pumping devices (13, 15) and the connection module (14) is configured so as to place at least the two first pumping stages (E1, E2, E3, E4) of the first pumping device (13) in parallel in order to obtain a predetermined, so-called normal, mass flow rate of the gases sucked by the sniffing probe (3).

6. Leak detection system (1) according to the preceding claim, wherein the normal mass flow rate lies between 200 cm³· min ¹ and 400 cm³· min ¹ in standard temperature and pressure conditions.

7. Leak detection system (1) according to any one of the preceding claims, wherein the first pumping device (13) comprises at least four pumping stages (E1, E2, E3,

E4) connected together by the connection module (14) in order to minimize the background noise.