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Technical Information
System Leak Test Methods
Systems, like individual parts, should be tested with the same pressure differential
and in the same direction as in actual use. Therefore, systems that are under
vacuum while in operation should be leak tested under vacuum, while pressurized
systems should be charged with helium to a pressure similar to operational
conditions when possible.
Vacuum Systems
In general, vacuum systems are tested with a portable leak detector. Typically the
leak detector is connected by means of a tee connected in between the foreline of
the high vacuum pump and the inlet of its backing pump. A system should be
capable of maintaining a foreline pressure low enough to operate the leak detector
at this location. Helium is supplied to potential leak site using a spray probe or
bagging suspected areas. If a leak exists, helium enters the system and rapidly
diffuses through it. The leak detector should respond within several seconds or
less. Leak detector sensitivity is diminished in systems with large backing pumps. If
a system is using a cryopump as a high vacuum pump, it must be valved off before
helium is introduced as cryopumps have limited helium pumping capacity
(see the following figure).
Figure 95 Vacuum System
Agilent Helium Leak Detector User Manual
Mount Test
Part
167
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