5.2.5 Integral leak detection
Integral leak detection is used to determine the total of all leaks (total leakage) in the workpiece. Here, too, the pump-down method and the sniffer method can be used.
Under the pump-down method, a workpiece is enclosed, filled with helium and the surrounding vessel evacuated. Or the workpiece is evacuated (vacuum system) and the surrounding space is filled with helium. In this connection, the enclosure can be a plastic film, or it can be a rigid vessel for commercial test systems. Under the sniffer method, the workpiece (e.g. an automotive fuel tank) is filled with helium and a given volume of gas is evacuated from the surrounding vessel through the leak detector's sniffer probe (Figure 5.4). The best result that can be obtained using the sniffer method is general confirmation that the workpiece is tight. However this method is not suitable for quantitative integral leakage rate measurement.
Figure 5.4:
Integral leak detection by means of the sniffer and vacuum methods
A pressure differential Δp = p1 - p2 = 100 mbar is sufficient when testing with an overpressure in the workpiece. Assuming laminar flow at the leak for the leakage rate QlΔp thus determined, this can be converted to value Ql for vacuum measurement at outside atmospheric pressure p0, in accordance with the following formula:
Formula 5-1:
Leakage rate conversion with differential pressure measurement
This conversion formula is derived from Formula 1-14 and Formula 1-21.
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35614 Asslar
Germany
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