An interesting example is calculated below, namely the difference in leakrate at the sniffer test, compared to a vacuum test. The leak geometry and the gas stay unchanged, also the pressure difference is 1 bar in both conditions. The difference is only: At the sniffer test the pressure conditions are 2 bar inner pressure against 1 bar (absolute) outer pressure, and at the vacuum test the outer pressure is 1 bar (atmosphere) and the inner pressure is zero bar (actually it is not zero. But for the calculation a 1/1000th of a bar is nearly zero).

Vacuumtest | |

Sniffertest |

The leakrate at the sniffer-test is three times larger than at the vacuum-test, even if it looks like the same pressure conditions.

When the type of gas changes, the leakrate changes in inverse proportion to the dynamic viscosities of the gases.