Inside-out leak testing: the part is filled with helium or a helium mix above atmospheric pressure, and a probe connected to the leak detector draws in air from around each joint. Sniffing is less sensitive than vacuum-mode testing, typically down to about 10⁻⁷ mbar·L/s, because the probe catches only part of the escaping helium and works against the helium already in the room. It is the usual method for gas lines, heat exchangers and parts that cannot be evacuated.
Pressure the gas stick to 30 psi helium and sniff every VCR fitting, slow passes, about an inch a second.
Also heard as
- sniffer test
- sniffer mode
- sniffing
Do not mix it up with
- Helium spray test: Spraying puts helium on the outside of an evacuated part, while sniffing looks for helium escaping from a pressurized one.
Related terms
Helium leak detector
Mass spectrometer tuned to helium that finds and measures leaks by detecting helium drawn into the system.
Helium spray test
Outside-in leak test: helium is sprayed on an evacuated part while a detector watches for it inside.
Helium bombing
Soaking sealed parts in pressurized helium so any leak lets helium in, then measuring how much comes back out.
Chase a leak
To hunt down a leak of unknown location joint by joint, often over hours, until the source is pinned down.