Pneumatic leak testing

Three different pneumatic measuring methods are used:

• the relative pressure method 
• the differential pressure method
• the leak test by means of flow measurement.

A leak test consists of four steps: filling, calming, measuring and venting. In the filling phase, the test item is pressurised with the test medium and separated from the pressure source after reaching the test pressure or a defined time. The settling phase compensates for temperature differences and turbulence created during filling, and allows time for narrow cross-sections to be penetrated and for seals to set.

The relative pressure method includes the pressure drop or pressure rise method. In the most common pressure decay method, the pressure in the test specimen is measured before and after the test time has elapsed.

In the differential pressure method, the test specimen and a reference volume are pressurised with a presettable pressure and separated from the pressure source after a settling phase.

In the leak test with flow measurement, the test item is filled with air and the pressure in the test volume is kept constant via air flowing in, so that the amount of air escaping due to leakage can be determined by measuring the amount of air flowing in. Either dynamic pressure measurement or mass flow measurement is used as the measuring method.