LEAK DETECTION IN A VISCOUS FLOW

Abstract

The invention relates to a device for vacuum leak detection, comprising a vacuum pump (18), a test chamber (12) which is designed to accommodate the test specimen and can be evacuated by means of the vacuum pump (18), and a gas detector (16) which detects the gas evacuated from the test chamber (12) by means of the vacuum pump (18), wherein the test chamber (12) has a plurality of vacuum connections (26) provided with the vacuum pump (18) in order to evacuate the test chamber (12), characterized in that a common pump volume (28) which is connected to the vacuum connections (26) is fluidically provided between the vacuum connections (26) and the vacuum pump (18) and is evacuated by means of the vacuum pump (18).

Claims

1-13. (canceled)

14. A device for leak detection comprising a vacuum pump, a test chamber configured to receive a test specimen and adapted to be evacuated by the vacuum pump, a gas detector detecting the gas evacuated from the test chamber by the vacuum pump, the test chamber being provided with a plurality of vacuum connections for evacuating the test chamber, the vacuum connections being connected to the vacuum pump, wherein a common pump volume connected to the vacuum connections is provided fluidically between the vacuum connections and the vacuum pump, which pump volume is evacuated by the vacuum pump.

15. The device according to claim 14, wherein the vacuum connections open into the pump volume.

16. The device according to claim 14, wherein the pump volume is formed in a wall, a bottom or a lid of the test chamber.

17. The device according to claim 14, wherein a plurality of the vacuum connections is connected to the pump volume each by a separate vacuum line, and the vacuum lines are substantially equal in length.

18. The device according to claim 14, wherein the pump volume is connected to the vacuum pump via a common pump line.

19. The device according to claim 14, wherein the vacuum connections are formed as holes and are distributed across at least one housing wall of the test chamber delimiting the test chamber volume.

20. The device according to claim 14, wherein the vacuum connections are distributed in a grid-like manner across at least one wall, a lid and/or a bottom of the test chamber.

21. The device according to claim 14, wherein the vacuum connections are arranged in a homogenously distributed manner.

22. A method for vacuum leak detection with a vacuum leak detection device comprising a vacuum pump, a gas detector and a test chamber, the vacuum pump evacuating the test chamber and the gas detector detecting a test gas in the gas evacuated from the test chamber by the vacuum pump, the test chamber comprising a plurality of vacuum connections connected to a common pump volume, the pump volume being formed fluidically between the test chamber and the vacuum pump, the method comprising the steps of: placing a test specimen in the test chamber, evacuating the pump volume and the test chamber such that a gas pressure gradient extending from the test chamber into the pump volume is greater than any gas pressure gradient extending transversely through the test chamber inside the test chamber.

23. The method according to claim 22, wherein the flow rate of the gas evacuated from the test chamber is higher inside the pump volume than inside the test chamber.

24. The method according to claim 22, wherein the difference between the gas pressures at two different locations inside the test chamber is negligibly small during the vacuum leak detection.

25. The method according to claim 22, wherein the vacuum pressure generated at the inlet of the vacuum pump and/or inside the pump volume is lower than 72 mbar.

26. The method according to claim 22, wherein the vacuum pressure generated inside the test chamber is higher than in the pump volume and is in particular lower than 80 mbar.

Description

[0013] Embodiments of the invention will be explained hereunder with reference to the Figures. In the Figures:

[0014] FIG. 1 is a schematic illustration of a first embodiment,

[0015] FIG. 2 is a schematic illustration of a second embodiment, and

[0016] FIG. 3 is a schematic illustration of a third embodiment.

[0017] In all embodiments, a test chamber 12 is connected to a vacuum pump 18 via a pump line 14 to which a gas detector 16 is connected. The vacuum pump 18 may be a diaphragm pump, a scroll pump or a rotary vane pump. The test chamber is typically formed by a plurality of walls 20, a lid 22 and a bottom 24. FIGS. 1 and 2 each illustrate the test chamber 12 in an open state, while the lid 22 is closed in a gas-tight manner in the direction of the respective arrows illustrated.

[0018] In the embodiments illustrates in FIGS. 1 and 2, the lid 22 is respectively provided with a plurality of vacuum connections 26 which, arranged in a grid, are homogenously distributed over the entire inner side of the lid 22. The vacuum connections 26 are formed as holes illustrated as points in the Figures. In FIGS. 1 and 2, the vacuum connections 26 open into a common pump volume 28 which is formed as a cavity in the lid 22 and is connected to the vacuum pump 18 via the pump line 14.

[0019] The embodiment illustrated in FIG. 3 differs from the embodiments illustrated in FIGS. 1 and 2 in that both the lid 22 and all of the walls 20 and the bottom of the test chamber 24 are each provided with a plurality of vacuum connections 26 which, in a simplified manner, are also illustrated as points. Each of the vacuum connections 26 is connected to the pump volume 28 via a separate vacuum line 30, the pump volume opening into the pump line 14. In the simplest case, the pump volume 28 may also be a section of the pump line 14.

[0020] After a test specimen not illustrated in the Figures has been placed in the test chamber 12 and the test chamber 12 has been closed, the vacuum pump 18 is used to reduce the pressure inside the test chamber 12 to 80, preferably less than 40 and particularly preferred less than 20 mbar. The pressure inside the test chamber is preferably less than 72 mbar, more preferred less than 36 mbar and particularly preferred less than 18 mbar.

[0021] If there is a leak in the test specimen, test gas will escape from inside the test specimen through the leak into the test chamber 12 and is drawn into the pump volume 28 through at least one of the vacuum connections 26. Due to the plurality of vacuum connections 26, the test gas only has to travel a comparatively short distance inside the test chamber before it reaches the pump chamber 28 via the respective closest vacuum connection 26. Compared to the conventional principle with only one vacuum connection, the plurality of vacuum connections 26 according to the invention reduces the relative distance of any location inside the test chamber to the closest vacuum connection 26. Thereby, the deviation of the time passing from the moment a leakage gas escapes to the moment it arrives at the detector, is smaller for different locations of a leak inside the test chamber that in the case of only one vacuum connection. Thus, the variance of this time is smaller for optional different positions of a leak inside the test chamber than in the case of only one vacuum connection.

[0022] As soon as the test gas has flown through the vacuum connection 26, the test gas is accelerated due to the lower pressure or the lower gas density in the pump volume 28. The diffusion rate or the flow rate of the pumped gas is higher in the pump volume 28 and the pump line 14 than in the test chamber 12.

[0023] Along a path between optional different points inside the test chamber 12, a gas pressure gradient forms in operation which is smaller than the gas pressure gradient forming along a path from a point inside the test chamber 12 to a point inside the pump volume 28.