Models 947, 948 and 960 Leak Detectors Operations and Service Manual
G-3
G.4 Various Methods of Testing for Leaks
There are many methods of testing for leaks in enclosures, systems or containers. The more
commonly used methods and their accuracy ranges are listed below:
Water Immersion
(Air Bubble Observation)
This method is good to approximately 10
−
3
atm 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.
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
atm 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
atm cc/sec. It tests for
ultrasonic sounds coming from a gas leak and for testing high
pressure lines.
Halogen
(sensitive to halogen elements
or compounds, especially
refrigerant gases)
This method is good to approximately 10
−
5
atm 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
atm 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
radiation required). It also requires a radiation safety officer.
Helium
This method is good to 10
−
11
atm cc/sec, and is capable of
finding leaks of any size larger. It is useful for testing hermetic
seals, vacuum enclosures, and vacuum systems, and is the most
versatile of industrial and laboratory leak detection testing
methods.