990 CLD Autoline™ Leak Detector
4-16
DRAFT 2/2/04
Leak Detector Self-Test
Accuracy, reliability, and stability of any mass spectrometer leak detector depends on the
leak-free integrity of its own vacuum system. Inherent helium background and its effect on
sensitivity demands elimination of all detectable leaks. If performance degrades during
operation or after some part of the vacuum system has been opened for service, a
methodical leak check can eliminate the possibility of a leak as the cause.
The following suggestions apply whether leak-checking components, systems, or the leak
detector itself:
❑
When spraying suspected leak locations, always apply helium sparingly, starting at
the highest points first, since helium rises. If drafts, such as from a cooling blower,
exist in the area, apply helium downstream from the source first, or deflect the draft
until leak checks are completed.
❑
If vent grooves exist at flanges or other assembled seals, apply helium sparingly to
these points rather than broadly spraying the area with helium. Minimizing the use of
helium saves time and increase the accuracy of locating the leak.
❑
Locate and repair large leaks before attempting to locate extremely small leaks.
❑
Limit search to a general area of the test piece by isolation methods. Bagging,
masking, or shielding with tape, plastic film, or duct seal, if applied properly,
shortens the time required to locate both large and small leaks.
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