Phrase for the slow, methodical job of finding a leak whose location is unknown: confirming it with a rate of rise or an RGA, then spraying, bagging and isolating sections one at a time. A leak that only opens up when hot, under vibration or when a particular valve moves can take days to chase. Experienced techs start with whatever seal was broken last.
Spent the whole night shift chasing a leak on the cluster tool, turned out to be a cracked weld on a water-line feedthrough.
Most leaks are at the last seal someone touched, so start with the flanges from the most recent maintenance.
Also heard as
- leak chasing
- leak hunting
Related terms
Leak check
To test a system or a joint for leaks, usually with a helium leak detector, after any break of vacuum.
Helium spray test
Outside-in leak test: helium is sprayed on an evacuated part while a detector watches for it inside.
Bagging
Enclosing a part or flange in a plastic bag filled with helium to check its overall tightness in one shot.
Virtual leak
Gas trapped in a hidden pocket inside the vacuum that bleeds out slowly and behaves like a small real leak.
RGA
Residual gas analyzer: a small mass spectrometer that identifies which gases remain in a vacuum chamber.