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.
