Bomb Chamber Leak Test

Infiltration Phase

Sealed components are placed inside a heavy-walled pressure vessel filled with helium gas at several atmospheres of pressure. Over a predetermined exposure period, the high pressure drives the tracer gas through any minute cracks or poorly welded joints into the component interior. This step, often referred to as bombing, requires precise control of both pressure and duration to ensure sufficient gas penetration.

If the component has a leak, the interior accumulates helium, creating an internal pressure of tracer gas. The duration of this phase depends on the expected size of the defect and the internal volume of the test object.

Detection Phase

After the bombing period is complete, technicians remove the parts from the pressure vessel and transfer them to a vacuum chamber. This chamber connects to a mass spectrometer that monitors the atmosphere for escaping helium. The vacuum draws the accumulated gas back out through the leak paths, where the sensor detects its presence.

Rapid transfer of the parts is necessary to prevent the tracer gas from fully escaping before measurement begins.

Accuracy Influence

Dust, oils, and surface contamination on the exterior of the test specimen can absorb helium during the pressurized phase. This surface-held gas then releases inside the vacuum chamber, producing a false leak signal that leads to unnecessary scrap. Rigorous pre-cleaning and drying of all parts before testing minimizes these erroneous readings.

Additionally, very large leaks may release all their tracer gas during the transfer period, necessitating a complementary coarse leak test.