Abstract: In the helium mass spectrometry leak detection technology, the multi-port composite molecular pump can meet different leak detection requirements by connecting to different air extraction ports, which broadens the application scope of traditional molecular pump. The location of the gas extraction port affects the pumping capacity of the molecular pump, which determines the performance of the leak detector. Based on the basic theory of molecular pump pumping, the calculation model of multi-port compound molecular pump is established. The pumping ports of medium check valve are set at different positions in the drag stage of molecular pump. The pumping characteristics are studied by combining with the actual use of mass spectrometer, and the influence of medium check position on helium leakage is analyzed. The optimal opening position under different leak detection conditions is obtained, which provides a theoretical basis for the structural optimization design of multi port composite molecular pump for leak detection. The results show that, when the medium detection port is set at the height between 15mm and 20mm, it can not only obtain better detection performance, but also ensure the allowable pressure of mass spectrometry chamber, and has a wide working pressure range.

Key words: multi-port compound molecular pump, medium detection valve, port position, drag stage, helium mass spectrometry leak detection