This method consists of evacuating the part through a pump group integrated in a system where a helium detector is included. Once the component internal pressure reaches the pre-set vacuum level, helium is applied on its external surface (or on the most critical areas only). The application of helium can be manual or automated. In the event of a leak, helium reaches the internal part of the component which is kept under vacuum during the whole process. At this point the helium detector senses an increase of the tracer gas concentration and, if this is higher than the pass/fail limit, the part will be classified as a reject.
As the test is based on the use of a pressure opposite to the operating one, manufacturers prefer not to rely on this method for the end-of-the-line leak test, which is always based on a vacuum chamber test. However this method is generally used as an intermediate leak test, performed before potentially leaking parts are assembled together for the creation of the complete product. By carrying out this test, substantial cost savings can be achieved, as a specific part of an assembly can be tested individually and, if required, re-worked before it is assembled into the final product. If this test is skipped, there are more chances to have failing assemblies which would eventually need, de-assembling, re-working, re-assembly and re-testing.
It is a rather cheap and precise solution, and given that it is also a dry test based on the use of helium, it represents a system well appreciated in many industrial sectors.