Leak testing is an essential part of quality assurance in series production, particularly in the automotive and aerospace industries. Pressure measurement is a common method for detecting leaks in components. This method is used to ensure that components remain tight under operating conditions and that no unwanted liquids or gases escape.
The measuring method: How the pressure measurement works
The pressure measurement method is one of the most frequently used methods in automatic leak testing. It is based on checking the pressure drop in a test specimen after it has been pressurized with air or another test medium. Although the escaping gas cannot be measured directly, its effects on the test pressure allow conclusions to be drawn about the leak rate.

The types of pressure measurement
There are two main types of pressure measurement: relative pressure measurement and differential pressure measurement.
Relative pressure measurement
With the relative pressure method, the test specimen is pressurized with air and examined for possible leaks after the adjustment phase. The PX25-L pressure sensor measures the pressure drop caused by a leak. This method is particularly suitable for smaller test volumes and is characterized by high operational reliability.

Differential pressure measurement
The differential pressure method is a more precise variant of pressure measurement in which both the test specimen and a reference part (test specimen with no leaks) are pressurized at the same time. After the adjustment phase, the differential pressure sensor PV2722 measures the pressure difference between the test specimen and the reference part. This enables the detection of very small leak rates, even at higher test pressures of up to 20 bar. This method is preferably used for applications with higher measurement accuracy requirements.

The measuring phase sequence for pressure measurement during leak tests
The test process for pressure measurement takes place in several phases, which ensure a stable and reproducible measurement process.
A typical automated leak test consists of the following four phases:

1. the filling phase
In this first phase, the test specimen is pressurized with compressed air. The air flows into the test volume and pressure builds up. Here it is crucial that the test volume is completely filled and that the pressure is evenly distributed. Any turbulence or pressure fluctuations should subside before the next phase begins.
2. the adjustment phase
After the test specimen has been pressurized, the adjustment phase follows. Here, the pressure in the test system stabilizes while the temperature changes caused by the filling process are compensated. For example, the air cools down during the expansion and heats up due to the compression in the test specimen. This phase is important to ensure that the measurements are carried out without interference from temperature changes or pressure fluctuations.
Compensation filling (shock filling) can be used to shorten the adjustment time. The test specimen is first filled with a slightly higher pressure than the actual test pressure. The pressure is then reduced to the test pressure, which leads to rapid cooling and thus accelerates temperature equalization.
3. the measurement phase
The actual measurement of the pressure drop takes place in this phase. The pressure drop is monitored by a differential pressure gauge or a relative pressure sensor. The aim is to determine the leakage rate resulting from the pressure drop during this phase. The pressure drop is directly proportional to the amount of air escaping and allows the leak rate to be determined accurately.
4. the venting phase
After the measurement, the test specimen is vented. This is done by opening a valve, which reduces the pressure in the test item to atmospheric pressure. The venting phase completes the test cycle and ensures that the test specimen is ready for further tests.
The advantages of pressure measurement for leak tests and leakage tests
The pressure measurement method offers several advantages, especially when used in automated production processes:
- High accuracy and repeatability:
Differential pressure measurement in particular enables precise determination of very small leak rates, even at high test pressures. - Fast measurement times:
By using compensation methods, the adjustment phase can be considerably shortened, which leads to a reduction in the overall test time. - Simple system design:
Relative pressure measurement only requires a sensor that is pressurized on one side and is therefore easy to integrate into existing systems.
DDM conclusion – Established and effective: pressure measurement for quality assurance in series production:
Pressure measurement is an established and effective method for leak testing components. It offers high accuracy and flexibility for both small and large-volume test specimens. Thanks to the clear structure of the measurement phase and the possibility of optimizing the process using compensation methods, this method is ideal for series production and enables an objective quality statement to be made with short test times.
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