This is a rare case. However, as vacuum pressures drop, even the most secure and flawless systems will soon be less tight. Tightness, or “the absence of leaks,” is necessary. These include: maintaining pressure/vacuum, product safety; environmental standards; and process efficiency. It is worth looking at leak detection and vacuum pumps new and used as two aspects of leak technology.
Leak detection
Different vacuum processes and applications require different leak rate requirements. What is acceptable at lower vacuum levels would be unacceptable at higher vacuum levels. A dry vacuum pumps is the only reliable method to detect leaks below 1×10-6mbar*l/s. The smallest leak rate is 1×10-12mbar*l/s, which equates to 1A.
How is helium used for detecting leaks?
Helium is used to detect leaks as a tracer gas for many reasons. Helium is very low in background level due to its small amount of 5 ppm in the air. Helium is also very mobile due to its low mass. It is inert/nonreactive. Helium is non-flammable, generally readily available, and very affordable. This is why vacuum coaters and coating is used as a tracer gas and mass spectrometer to measure and analyze the leak. Helium is a light tracer gas that is very fast and completely harmless.
Helium Leak Detection
The following method is used to detect helium: Helium is either pumped from the outside or inside the unit. Any gas that may have been released is collected and pumped into a mass spectrometer to be analyzed. Anything above the background trace is considered evidence of helium leakage. The spectrometer works by following the same principle: Any helium molecules that are sucked into it will be ionized. These helium ions will then “fly” into the trap, where the ion current will be analyzed and recorded. The leak rate can then be calculated based on the ionization current.
