Pfeiffer Vacuum

5.2.4 Local leak detection

Local leak detection is used to identify leakage in a workpiece.

Under the pump-down method, the workpiece (vessel) is connected to the leak detector, and helium is briefly sprayed onto a suspicious area by means of a spray gun. If the pressure in the workpiece is in the molecular flow range, i.e. less than 10-3 mbar, there will be an immediate display as a result of the high velocity of the helium atoms. At higher pressures, particularly in the laminar flow range that starts at 1 mbar, the display speed will be much slower and will be governed by the pumping speed of the leak detector's backing pump.

Under the sniffer method (Figure 5.3), the workpiece (3) is filled with a helium overpressure. A sniffer probe (2) is connected to the test gas connection. The helium that escapes through leaks in the workpiece can be detected by sniffing with the probe.

(Figure 5.3)zoom figure
Figure 5.3: Local leak detection by means of the sniffer and vacuum methods

Individual leaks can be identified using local leak detection. However the sum of all leakage cannot be determined. That is why this process offers only limited suitability for providing a GO/ NO GO indication for quality assurance purposes.

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