Leak testing methods

ZELTWANGER specializes in all test methods using air as a testing medium. The main principle of our leak testing measurement is based on two underlying methods: pressure variation measurement and flow measurement. In both methods, the test item is first filled with air to a specified testing pressure and then disconnected from the compressed air supply. After it's disconnected is when the actual measuring begins.

Pressure variation measurement

In this method, the variation in pressure is used to identify a leak. If there is a leak, it causes a change in pressure that can be calculated as a leakage rate based on the test volume and the measurement time. This method can also be performed as a vacuum test.

Flow measurement

In the flow measurement method, a measurement signal is emitted, which is the same, regardless of the size of the test volume and the measurement time, and which correlates to any leakage present. No calculation is required for this, unlike with the pressure variation method.

An overview of the different leak testing methods:

Relative/absolute pressure

The relative or absolute pressure method permits a compact test set-up and is characterized by good operating reliability and a wide measurement range. In this case, the test specimen is placed under pressure and the pressure differential is determined over the set time.

With the relative pressure method, the differential to the ambient pressure is measured. This is why this is known either as overpressure testing, if the test pressure is greater than the ambient pressure, or vacuum testing if the pressure is lower than the ambient pressure.

When using the absolute pressure method, the test pressure is determined relative to the absolute zero point (absolute vacuum). The resolution depends on the test volume and the test pressure. This method permits a resolution of 1 Pa.

Relative/absolute pressure

Mass flow

The mass flow method works according to the calorimetric principle (thermal method). The result is made available directly in cm³/min and after offsetting with the volume factor between the reference and test volume, corresponds directly to the leakage rate. For testing, both the test specimen and the reference volume are pressurized. Following a settlement phase, the mass flow and the flow direction between the reference and test volume are determined.

Mass flow method

Differential pressure

The differential pressure method permits a compact set-up and is characterized by good operating reliability and a wide measurement range. In this case, the test specimen and a reference volume are placed under pressure and the pressure differential (pressure change) is determined over the set time. This method permits a resolution of >0.1 Pa.

Differential pressure

Radial shaft seal measurement

Leak testing using a radial shaft seal takes place in two steps:

1. The main test chamber (e.g. oil chamber) is placed under pressure. Here, the bypass valve between the oil chamber and the shut-off area remains closed. During the settling phase, if there is a leak at the radial shaft seal, after a short time a stable flow will be established against the atmosphere at the mass flow sensor. This is measured in cm³/min.

2. After conclusion of the first measurement phase, the valve upstream from the mass flow sensor is closed and the bypass to the shut-off area is opened. During the test which is then performed, the leakage of the main chamber (e.g. oil chamber) is determined. Any possible lack of leak tightness at the radial shaft seal is neutralized as both chambers are linked through the bypass.

Radial shaft seal measurement