Vacuum Leak Testing operates on the reverse principle of the pressure decay method. In this technique, the component is evacuated to a predetermined low-pressure level. After allowing the pressure to stabilize, any rise in internal pressure is monitored over time. The increase in pressure indicates the entry of external air into the part, signifying leakage.

This method is suitable only for components that can withstand external atmospheric pressure. Parts that are structurally weak, such as thin-walled plastic components, are not recommended for vacuum testing due to the risk of deformation or collapse.

The Vacuum Decay Method can be implemented as a fully automated process, ensuring consistent results and eliminating operator dependency. It functions as a “go / no-go” test, identifying whether a leak is present in the system. While it accurately detects total leakage, it does not pinpoint the exact leak location, and multiple leaks may exist within the tested component.