6. The inside-out method, and its opposite, outside-in

Measuring total leak-rate – inside-out

A part pressured at a defined pressure and a known helium concentration is placed in a vacuum chamber pumped by a leak detector or leak detector system.

helium inside out

By using this test method, it is possible to measure the total outflow of helium from the part in a calibrated way. (This technology does not allow to pin point the leak location(s).

 

Measuring total leak rate – outside-in

The part to be tested is evacuated by a vacuum pumping system. When the appropriate cross over pressure is reached, the leak detector is valved in.
outside in helium
At the same time, the part is covered by an enclosure. Helium is admitted into the enclosure and if there is a leak(s), the helium will enter the part. The detector is now able to measure the total leak value (includes multiple leaks), if the helium concentration and pressure in the enclosure are known.

Also in this method, the location of the leaks will not be known.

Do note:
The leak reading will not be correct if the enclosure does not contain 100% of helium. (The enclosure needs to be pre-evacuated to reach this objective).

After removing the enclosure, the operator can spray helium using a spray probe to “pin pointing” the exact leak location(s).

To read about the accumulation method please click here.