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Helium mass spectrometer


A helium mass spectrometer is an instrument commonly used to detect and locate small leaks. It was initially developed in the Manhattan Project during World War II to find extremely small leaks in the gas diffusion process of uranium enrichment plants. It typically uses a vacuum chamber in which a sealed container filled with helium is placed. Helium leaks out of the container, and the rate of the leak is detected by a mass spectrometer.

Helium is used as a tracer because it penetrates small leaks rapidly. Helium has also the property of being non-toxic, chemically inert and present in the atmosphere only in minute quantities (5 ppm). Typically a helium leak detector will be used to measure leaks in the range of 10−5 to 10−12 Pa·m3·s−1.

A flow of 10−5 Pa·m3·s−1 is slightly less than 1 ml per minute at standard conditions for temperature and pressure (STP).

A flow of 10−13 Pa·m3·s−1 is slightly less than 3 ml per century at STP.

Typically there are two types of leaks in the detection of helium as a tracer for leak detection: residual leak and virtual leak. A residual leak is a real leak due to an imperfect seal, a puncture, or some other hole in the system. A virtual leak is the semblance of a leak in a vacuum system caused by outgassing of chemicals trapped or adhered to the interior of a system that is actually sealed. As the gases are released into the chamber, they can create a false positive indication of a residual leak in the system.

Helium mass spectrometer leak detectors are used in production line industries such as refrigeration and air conditioning, automotive parts, carbonated beverage containers food packages and aerosol packaging, as well as in the manufacture of steam products, gas bottles, fire extinguishers, tire valves, and numerous other products including all vacuum systems.


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