Checking coating systems for leak tightness
After installing a new system or maintaining an existing one, leaks occur often. This is often due to joining errors or forgotten or defective seals. Correct handling of helium leak detectors is crucial for finding these leaks and controlling equipment for tightness. The more is known about the physical phenomena underlying the leak test as well as the optimization possibilities during testing, the easier it is to use helium leak detectors in practice. This also leads to more reliable measurement results. The following overview provides practical information on the correct handling of helium leak detectors and the successful implementation of leak tests on vacuum systems.
What needs be considered when connecting the leak detector to a coating system?
Leaks that occur after start-up or maintenance of vacuum systems are often very large. However, commercially available helium leak detectors can no longer be used from a certain leak size on. Their maximum working pressure is usually between about 6 and 25 mbar. If there are large leaks, this pressure may not be reached during evacuation. Figure 1 shows a Si3N4 coating system. After maintenance, only a pressure of 80 mbar is reached during evacuation.
Instead of throttling a vacuum leak detector, the Pfeiffer Vacuum ASM 340 leak detector can be used to create a qualitative massive leak detection mode, which helps to localize the present leak.
Integrating the helium leak detector in a coating system
Process pump to support the leak detector
Optimally, the leak detector should be connected to the fore-vacuum line of a vacuum system as shown in Figure 1 and 2. To protect the leak detector, which is designed for use in clean environments, from severe thermal stress due to the compression heat generated during pumpdown, an additional process pump may also be used. It is insensitive to the thermal stress and also pumps off all outgassings, vapors and any stirred up particles.
The use of an additional process pump can increase the availability of the leak detector and significantly extend its maintenance intervals. This results in considerably reduced operating costs.