The helium leak testing takes advantage of the relatively small size of the helium atom as the indicating gas for detecting the smallest of leaks. Therefore, it is a valuable test in searching for leaks in brazed assemblies.

After brazing, an assembly is placed directly on the unit and the unit’s pumps evacuate the area within the assembly to the necessary low vacuum level. Helium gas is then released around the outside of the assembly. If a leak is present, the gas analyzer in the unit alarms and the leak point may then be identified.

With standard helium leak detection equipment a leak rate as low as 1×10-9 cc/second can be detected. A leak this size would take approximately 3.17 years to leak one cubic centimeter of helium through the leak. This makes it sufficiently sensitive to use as an acceptance test on the most critical of components.