The part is placed under a
cover, into which helium is
injected.
The leak cannot be located.
Potential leaking areas are
sprayed with helium.
The leak can be located.
Global test
part
spray probe
detector
Spray test
Response time
Spray method
(inboard testing)
Helium concentration
and signal displayed
When spraying starts, the leak signal is not displayed instantaneously
on the analyzer:
there is a response time which depends on the volume V being tested
and the helium pumping speed S of the system at the opening of the
part, according to the following relation:
T = V/S (T in seconds, V in litres, S in l/s)
T is the time required for the signal to reach 63 % of the final value.
The detector measures the flow of helium penetrating the part.
This involves removing air from the test part, connecting it to the
analyzer and then spraying helium over the outer surface.
In accordance to the He concentration rate in the gas used for the
leak detection, the signal displayed will change.
Example: signal displayed with a 1x10
-7
mbar.l/s calibrated leak
(with 100 % He) connected to the detector inlet.
% He in the gas used 100 % 10 % 1 %
Signal displayed
on the leak detector
1x10
-7
mbar.l/s 1x10
-8
mbar.l/s 1x10
-9
mbar.l/s
or
part
detector
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