INFICON :: LEAK TEST - Best Practices for Leak Detection

Carrier Gas Leak Detection

Using sniffer leak detectors on large objects or difficult to access test areas usually results in long test times and overall long test sequences. Using carrier gas leak detection, where the leak gas flow is transported to the leak detector by an additional carrier gas flow under atmospheric pressure, can help get the leak signal to the sniffer much faster.

To illustrate how carrier gas leak detection works, let’s look at the design of a test object; an electronic box with a weld seam, an O-ring sealed lid, a lamp and three plugs. The test object is filled with tracer gas under a light overpressure.

Normally, to test this object with a sniffer probe you would need to point the probe tip at all suspicious points and along the seams (see arrows).

Example 1: Integral test chamber
Another way is to carry out a leak test in a chamber with a carrier gas flow. If the test object and the net volume of the chamber are small, the sniffer probe can be positioned at the outlet flow point to analyze the gas flow (see below).

Specifications for Example 1:
Net volume of the chamber: 100 cm3
Pumping speed of the sniffer: 3000 sccm = 50 cm3/s

The tracer gas from a leak at any point of the test object will reach the sniffer probe in approximately 2 seconds. Sensitivity of this test format is 100% because all the test gas is sucked directly into the sniffer probe.

Example 2: Larger test object and chamber
Detecting leaks from a more voluminous test object requires a bigger test chamber and an increased carrier gas flow for a quick response time. This flow is typically generated by a fan (see below).

Detection of the correct leak rate needs a bit more calculation when using this configuration.

Specifications for Example 2:
Length of the test object: 600 mm
Net volume of the chamber: 50 liter
Air flow by the fan: 36m3/h = 10 liter/s = 104cm3/s
Pumping speed of the sniffer: 3000 sccm = 50 cm3/s

The response time is still relatively short, but sensitivity is reduced by a factor of 200 because of the high dilution of the tracer gas in the total carrier gas flow.

According to the requirements of the application, the fan speed should be carefully calibrated to optimize response time and sensitivity.


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