7.2.3 Test methods
The test procedure used to detect leaks depends upon the type of test specimen and the required test results. The following criteria are formulated in the standard DIN EN 1779 :
- Will the test specimen be tested at overpressure or in a vacuum? In selecting the test method, if possible a method should be chosen that takes into account the pressure gradient encountered when the test specimen is actually used.
- Is only a partial area or the whole area of the test specimen to be tested?
- Should local leak detection, which is used to find leaks, be carried out or should integral leak detection, where the leakage rate of test specimens is typically determined for quality assurance purposes, be performed?
Leak detectors are equipped for two operating methods:
- The vacuum method, in which the test specimen is evacuated and helium exerts its effect from the outside.
- The sniffer method, in which the workpiece is filled with test gas overpressure $\Delta p$ > 100 hPa and the escaping test gas is sucked into the leak detector via a sniffer valve and detected.