Pressure Decay/Rise Testing
Pressure testing can be used to detect larger leaks requiring correction prior to the component undergoing a more sensitive, Mass Spectrometer/Leak Detector test. Unless there is significant time available, Pressure Decay is the least sensitive of all the techniques discussed here but does have a very valuable role to play in the production scenario. The technique looks for a changing pressure in a sealed (and therefore constant if no leak is present) part and can be implemented in two ways:
Pressure Decay - The part to be tested is pressurized with gas and sealed. The system monitors the internal pressure and looks for a drop over time.
Vacuum Rate of Rise - The part to be tested is evacuated and sealed. The system monitors the internal pressure and looks for a rise over time.
Clearly, the more time spent, the better the sensitivity of the test. However, care must be taken not to confuse changes associated with temperature and out-gassing with the presence of a leak. This technique is very valuable in 'weeding out' major leaks, saving valuable Go-No-Go test time, uses less expensive (compared to Helium) air or dry nitrogen as the test gas. VTI systems can be supplied with 'dual ports' allowing two units to be tested in parallel. This doubles the sensitivity of the system without loss of production rate in the production scenario.
