Application of spiromolecular pumps in helium leak detection

Abstract

Helium leak detection has developed from a laboratory technique for vacuum physicists to a standard method of industrial quality control. This came along with new requirements from the user of leak detection equipment. Ease of use is one of them; fast cycle time (this means leak detection at high pressures) is another one. While the first demand can be satisfied by microprocessor control of the leak detectors functions, the latter implies new concepts in the design of the vacuum system. The molecular pump of the Holweck type, rediscovered not long ago, now called the spiromolecular pump, offers some interesting properties for leak detection application. The large difference in compression ratio of the Holweck stage for light and heavy gases is advantageous for counter-flow leak detection. The dynamic seal offers a high compression ratio to ensure low noise levels even with small mechanical fore pumps. The mass-flow characteristics offer high pumping speed at high test pressures. Experimental data on spiromolecular pumps are discussed and examples of new helium leak detectors utilizing these pumps are presented.