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Calculation of an example

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

$q_A = 5 \cdot 10^{-5} \, {\textup{mbar l} \over s }$

$p_{A1} = 1 \, bar$

$p_{A2} = 0 \, bar$

Sniffertest

$q_{B} = \, ?$

$p_{B1} = 2 \, Bar$

$p_{B2} = 1 \, Bar$

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.