Varian 990 dCLD II, Operation Manual

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Model 990 dCLD II Component Leak Detector
C-3
C.4 Various Methods of Testing for Leaks
There are many methods of testing for leaks in enclosures—either systems or containers.
The more commonly used methods along with the range of accuracy provided are listed
below:
Water Immersion
(Air Bubble
Observation)
This method is good to approximately 10
−
3
std cc/sec, and can be
more sensitive if internal pressure is increased or vacuum is created
above water pressure. This method is limited because of difficulty in
differentiating between leakage bubbles and surface desorption bub-
bles. It is used to test industrial items such as valves, hydraulic com-
ponents, castings, automotive and air conditioning components.
Dye Penetrant A special dye, applied to one side of a surface suspected to contain
a leak, seeps through the leak and appears on the other side. This
method can take an hour or more for a 10
−
4
std cc/sec leak to show
up. This test is inexpensive but destructive in some applications, as
well as slow and messy.
Ultrasonic This method is good to approximately 10
−
3
std cc/sec. This method
tests for ultrasonic sounds coming from a gas leak and is used for
testing of high pressure lines.
Halogen
(sensitive to
halogen elements
or compounds,
especially refrigerant
gases)
This method is good to approximately 10
−
5
std cc/sec in most cur-
rent applications, but extendable to 10
−
9
std cc/sec under some
limited situations. It is critically dependent on operator judgement
if leaks are below 10
−
5
std cc/sec and requires constant flow of
fresh air in the test area because of the tendency of trace gas to
hang in the area. The detector used in this method is sensitive to a
variety of gases from external sources such as cigarette smoke and
solvent fumes.
Radioisotope This method is useful only for testing hermetically sealed cavities. It
has approximately the same range as the helium method but it
involves an expensive installation (from four to ten times the cost of
a helium installation depending on the degree of isolation of radia-
tion required). It also requires a radiation safety officer.
Helium This method is good to 10
−
11
std cc/sec, and is capable of finding
leaks of any size larger. It is useful for testing hermetic seals, vac-
uum enclosures, and vacuum systems, and is the most versatile of
industrial and laboratory leak detection testing methods.