Vacuum Testing
The spectrometer tube is connected to a
vacuum pumping system and operates under high vacuum; an
auxiliary roughing pump evacuates the object to be tested and a
sample of the gas being pumped enters the spectrometer tube.
The operator sprays the outside with a fine jet of
helium; if a leak exists, the helium enters through the flaw
due to the pressure differential and is immediately sensed by
the mass spectrometer tube. Since air contains only a
relatively insignificant amount of helium, helium will enter
the leak detector only in the event of a leak that has been
probed. The entire object may be blanketed with helium gas for
a quick total leakage test, or the exact position of a leak may
be found by probing with a fine spray of helium.
