INFICON :: LEAK TEST - Best Practices for Leak Detection

Leak Test Comparison: Carrier Gas Mode vs. Pressure Decay
Advantages of the new T‑Guard™ Leak Detection Sensor

There are several methods of leak testing. In this article, we compare (differential) pressure decay, a fairly widespread method, with a new integral helium testing method at atmospheric pressure in carrier gas mode.

The pressure decay method is easy to understand and to carry out, with relatively reliable results. However, there are recognized shortcomings with respect to temperature, size, humidity, surface and flexibility of the parts being tested:

  • Temperature variation: As pressure is closely related to temperature, every variation in temperature will simulate a leak or suppress a true leak.
  • Test object size: It is a well-known fact that a small leak in a small part will result in a higher pressure difference than a small leak in a big part. That’s why pressure decay is limited to parts well below 5 liters (1.3 gallons) in volume.. But even with very small parts, the tested leak rate cannot be below 1x10-3 mbar l/s. With a part of 1 liter inner volume, the tested leak rate might not even be in the 10-1 mbar l/s range, making testing for water tightness unfeasible.
  • Humidity: Humidity is problematic for pressure decay because every fluid generates a constant pressure of its own (vapor pressure), also influencing temperature.
  • Test speed: The (inner) surface of the test object influences the measurement speed because it changes the time needed for the internal pressure to stabilize.
  • Flexible parts: These cannot be tested at all because flexible parts try to maintain a constant internal pressure.

One of the two automatic measurement modes in the new INFICON T‑Guard Leak Detection Sensor features a carrier gas mode, which is outlined below. The test object is pressurized with (diluted) helium, which will escape through any leak. By putting the test object in a chamber and generating a constant gas stream around the object, T‑Guard can detect the smallest amounts of helium in the gas stream. Through intelligent design and enhanced software, the T‑Guard Leak Detection Sensor is able to identify the total leak rate of the test object. The test specifications include:

  • Leak detection in the range of 10-5 mbar l/s in less than one minute for small parts and chambers
  • Leak detection in the range of 10-3 mbar l/s in less than one minute for larger parts with a volume of several liters (not possible with pressure decay)

Leak detection measurement with T‑Guard Leak Detection Sensor provides the following advantages:

  • Temperature independence
  • Scalability to any size, together with the leak rate
  • Unaffected by humidity
  • Inner surface of the test object is irrelevant
  • Flexible objects can be tested
  • Higher sensitivity (100x more sensitive than differential pressure decay)
  • No maintenance needed for the measurement device

How the Carrier Gas Method Works
In carrier gas mode, a suitably sized stream of air passes around the test object. This stream transports helium from any given leak to the T‑Guard™ Leak Detection Sensor, which measures the helium concentration in the gas stream and reports the actual leak rate to the user.


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Spring 2009
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