Varian 990 dCLD II, Operation Manual

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C-1
Model 990 dCLD II Component Leak Detector
Appendix C. Introduction to Leak Detection
C.1 Leak Testing—Why is it Needed?
Even with today's complex technology it is, for all practical purposes, impossible to manu-
facture a sealed enclosure or system that can be guaranteed leak proof without first being
tested. Through the use of modern mass spectrometer leak testing techniques, as imple-
mented by the 990 dCLD II Helium Leak Detector, leak rates in the 10
−
9
std cc/sec range
can be reliably detected. The discussion that follows provides a brief summary of specific
information pertinent to the overall subject of leak detection.
C.2 Classes of Leak Detection
There are four general classes of leak detection:
Hermetic Enclosures
(or parts thereof)
These are tested to prevent entrance of contaminants or loss of fluid
that would affect performance of the enclosed unit. Examples: elec-
tronic devices, integrated circuits, sealed relays, motors, ring pull
tab can ends, and multipin feedthroughs.
Hermetic Systems These are tested to prevent loss of fluid or gas within. Examples:
hydraulic systems and refrigeration systems.
Evacuated Enclosures
(or parts thereof)
These are tested to prevent too-rapid deterioration of vacuum with
age. Examples: TV picture tubes, bellows sensing elements,
full-panel opening can ends, etc.
Vacuum Systems These are tested to minimize inleakage and allow attainment of
better vacuum or higher gas removal ability at any given vacuum
(absolute pressure).