In this guide
How each method works
Pressure decay fills the part with air to a set pressure, isolates it and watches for a drop. A leak lets air escape and the pressure falls. It is simple and cheap to run, but temperature changes, part flexing and large internal volumes all affect the reading, which limits how small a leak it can detect reliably.
Helium testing uses helium as a tracer gas and a mass spectrometer leak detector that responds only to helium. Because the detector measures the leaking gas itself rather than a pressure change, it can find far smaller leaks and is much less affected by temperature or part volume.
Side-by-side
| Smallest leak found reliably | Helium: very small leaks, orders of magnitude finer. Pressure decay: larger leaks, typically in the 10⁻³ mbar·l/s range and above, depending on part volume. |
|---|---|
| Running cost | Helium: gas cost per test, reduced sharply with recovery. Pressure decay: compressed air only. |
| Machine cost | Helium: higher (detector, vacuum pumps, chamber). Pressure decay: lower. |
| Effect of temperature and volume | Helium: small. Pressure decay: significant. |
| Finds leak location | Helium sniffer: yes. Pressure decay: no. |
How to decide
- Start from the reject limit in your specification. If it is tighter than pressure decay can reliably hold for your part volume, you need helium.
- Consider what the part will contain. Refrigerants, SF6, coolant and fuel usually call for helium-level tightness.
- Compare total cost per part, including rejects and warranty claims, not only machine price. Helium recovery lowers gas cost.
- For mixed requirements, an air pre-test followed by helium testing catches gross leaks fast and protects the detector.
Still unsure? Send us your part details and we'll recommend the method before quoting a machine.