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TIP OF THE MONTH 08

QUESTION: Help, my leak detector is contaminated! What can I do?

ANSWER: Act as quickly as possible and purge the leak detector’s vacuum system with an inert gas that contains a very low Helium concentration.

BACKGROUND: The vacuum system of helium leak detectors is assembled with elastomer seals which can be penetrated by helium if present in high concentrations. If the concentration drops again, the helium will escape but very slowly and this can lead to an increased background signal.

The oil from rotary vane pumps, interior surfaces and particles of dirt on those surfaces also have what is known as a “helium memory”. If the leakage test indicates contamination, e.g. a serious leak or operating error, the helium should be purged from the equipment as quickly as possible to prevent it from penetrating the elastomer seals.

Depending on the level of accuracy required, this can be carried out using air or, if searching for very small leaks, with helium-free nitrogen.

adixen leak testers have an automatic antipollution safety cut off, which closes the test valve if the signal suddenly exceeds a specified threshold during the test cycle. This effectively prevents further contamination.

However, the device should not be simply left in this state. Repeated ventilation with inert gas that has a very low helium concentration followed by evacuation will reduce the background signal faster than simply running in standby mode. When installing a leak detector into an automatic system it is always a good idea to incorporate a decontamination programme. It is possible to switch off automatic antipollution if necessary.