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Technical Information
Introduction to Leak Detection
Leak Testing—Why is it Needed?
Helium is a superior choice of tracer gas used to find leaks for a multitude of
reasons. Helium is:
Non-toxic
Inert and non-condensable
Normally not present in the atmosphere at more than trace amounts
Relatively inexpensive
Readily passes through leaks due to its small atomic size
Non-flammable
Available in various size cylinders
Available in purities appropriate for medical usage.
The only molecule smaller than Helium (mass 4) is Hydrogen (mass 2), which is not
inert. Helium is much lighter than the next heavier inert molecule, Neon (mass 20)
which is much more expensive. Helium is present at a concentration of only 5 ppm
in normal atmospheric conditions.
Agilent's Helium Leak Detection Technologies
A Mass Spectrometer Leak Detector (MSLD) is a complete system for locating
and/or measuring the size of leaks into or out of a device or a container. This
method of leak detection is initiated when a tracer gas, helium, is introduced to a
test part that is connected to the MSLD system. The helium leaking from the test
part diffuses through the system, its partial pressure is measured, and results are
displayed on a meter.
The MSLD operating principle consists of ionization of the gases in a vacuum and
their acceleration across a voltage drop and a magnetic field (Figure 88). The
helium ions are separated and collected, and the resulting ion current is amplified
and indicated on the meter or display.
Agilent Helium Leak Detector User Manual
161
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