The pressure increase test

At the pressure increase test the test object first is evacuated. Then the pressure increase is measured over time. The disadvantage of the pressure decrease test, namely the difficulty to messure very fine pressure changes at a high total pressure is not so present with the pressure increase test, because the amount of gas at begin of the test is much lower and the pressure increase cannot become higher than 1 bar.

Of course at the begin of the test there is a non linear pressure increase coming from the degassing of the inner walls and this is mostly humidity. When the pressure has increased above the water vapour saturation pressure, the pressure change becomes a linar function. This makes it necessary to have a graphic plot of the measurement. Then from the linear part of the curve the leak rate again can be calculated from volume, pressure difference and time.