Coating systems
After installing a new system or maintaining an existing one, leaks occur often. In many cases, this is due to joining errors or forgotten or defective seals. Correct handling of helium leak detectors is crucial for finding these leaks and checking the 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 cannot be used for leaks above a certain size. 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 Si~3~N4 coating system. After maintenance, only a pressure of 80 mbar is reached during evacuation. In order to be able to carry out leak detection at such high working pressures, the ASM 340 leak detector from Pfeiffer Vacuum features a qualitative massive leak detection mode that can be used to locate the existing leak.
Si~3~N4 coating system
Integrating the helium leak detector in a coating system process pump to support the leak detector
Ideally, the leak detector should be connected to the fore-vacuum line of a vacuum system. To protect the leak detector, which is designed for use in clean environments, from severe thermal stress due to the compression heat generated during pump down, an additional process pump may also be used. It is insensitive to the thermal stress and also pumps off all outgassing, 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.
