Wrapping a component, a flange or a whole system section in a plastic bag or hood and flooding it with helium while the inside is pumped by a leak detector. The reading gives the total leak rate of everything inside the bag, and shrinking the bag down to single joints narrows down where the leak is. The formal name is a hood test.
Heard on the job
Spray isn't finding it, bag the whole bottom manifold and see if the number moves at all.
Also heard as
- bag test
- hood test
- tenting
Related terms
Helium spray test
Outside-in leak test: helium is sprayed on an evacuated part while a detector watches for it inside.
Helium leak detector
Mass spectrometer tuned to helium that finds and measures leaks by detecting helium drawn into the system.
Chase a leak
To hunt down a leak of unknown location joint by joint, often over hours, until the source is pinned down.