990 CLD Autoline™ Leak Detector
6-4
DRAFT 2/2/04
Methods of Testing for Leaks
There are many methods of testing for leaks in enclosures — either systems or containers.
The more commonly used methods and their accuracy ranges are listed below.
Water Immersion (Air Bubble Observation)
Probably the oldest method, water immersion 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 bubbles. It is used to test industrial items such as valves,
hydraulic components, castings, automotive, and air conditioning components, because of
its low cost.
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 current 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 degree of isolation of radiation
required.) It also requires a radiation safety officer.
Helium Method
This method is good to 2 x 10
-12
* std cc/sec, and is capable of finding leaks of any larger
size. This method is useful for testing hermetic seals, vacuum enclosures, and vacuum
systems. It is the most versatile of industrial and laboratory leak detection testing methods.
* Using Vacuum Technologies Model 960 or another equivalent system.
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