The standard vacuum-mode leak test: the system is pumped by or connected to a helium leak detector, and a fine helium jet is played over welds, flanges and feedthroughs from outside. When the signal jumps, the leak is near the nozzle. Testers start at the top because helium is lighter than air and rises, use the smallest flow that gives a signal, and wait out the system's response time before moving on.
Start the helium spray test at the top port and work down, little puffs, five seconds a spot.
Also heard as
- spray test
- outside-in test
- vacuum mode test
- spray down
Related terms
Helium leak detector
Mass spectrometer tuned to helium that finds and measures leaks by detecting helium drawn into the system.
Sniff
To hunt for helium escaping from a pressurized part by sweeping a sniffer probe slowly over joints and welds.
Bagging
Enclosing a part or flange in a plastic bag filled with helium to check its overall tightness in one shot.
Chase a leak
To hunt down a leak of unknown location joint by joint, often over hours, until the source is pinned down.
Hang-up
Helium that lingers in a leak detector or system after a big hit, holding the signal high and masking small leaks.