| As an important equipment for obtaining high vacuum in helium mass spectrometry,compound molecular pump is an indispensable key component of helium mass spectrometer leak detector.Its pumping characteristics directly affect the performance of the leak detector.In recent years,with the continuous development and progress of high-vacuum leak detection technology,the performance requirements of the instrument are getting higher and higher,and the design of the molecular pump also undergoes great changes.In particular,multi-port compound molecular pump was developed,it combines the features of downstream leak detection and counter-current leak detection,and broaden the application of the traditional leak detector to make it more convenient and flexible in the testing process.Therefore,research on multi-port compound molecular pump has important theoretical significance and practical value.Based on the theory and calculation method of traditional compound molecular pump,This paper studies multi-port compound molecular pump.A gas shunt calculation model was established by analyzing the vacuum system of the leak detector,and the relevant calculation program is compiled to improve the calculation effectiveness.The calculation accuracy was improved by using the integral mean method and section by section identification flow method.According to the data of prototype F-63 compound molecular pump provided by"Molecular Pump Special",The influence of parameters such as turbine blade inclination,blade number,blade height,blade thickness and helix angle of traction tube,traction slot depth,rotor and stator clearance on the pumping performance of the molecular pump is analyzed by using calculation software and making heavy calculations.The pumping performance of air and helium were compared.In order to improve the return flow of helium,An optimization and improvement solution for its pumping characteristics was proposed,which can be better applied to the leak detection technology.Aiming at the two mediums of air and helium involved in the leak detection process,the similarities and differences between the turbine blades on the pumping speed of different kinds of gases were analyzed.The difference between pumping speed of the two gases is very small by plotting the Hmax with C changes graph and deducing the formula.Secondly,the airflow characteristics of the leaky hole are analyzed.The ratio of leak rate of helium to air in different flow regimes was obtained with conduction calculation.Molecular flow is more conducive to the detection of helium and the results is validated by calculation model.In order to give full play to the advantage of counter-current leak detection,the selection of the position of the exhaust port of the multi-port compound molecular pump was optimized.Based on the calculation model,the parameters of HLT 550 helium mass spectrometer leak detector were taken as an example to calculate and analyze the pressure value of different suction ports and the change law of the two kinds of gas regurgitant flow with the opening position.And from different points of the working pressure of the suction port,Hole leakage rate,the allowable pressure in the mass spectrometer chamber and the minimum leak rate of the instrument,the influence on the position of extraction port was analyzed.concluded that:the turbine level 8 to 10 between the leaf columns,In the traction level to choose the traction height of 15mm to 20mm were set up in the fine check valve and check valve can get better suction characteristics.In summary,this paper through the establishment of multi-port compound molecular pump model,the use of procedures to assist a large number of calculations,analysis and discussion of its application to helium mass spectrometry leak detection technology.Based on F-63 compound molecular pump prototype,a series of optimization and improvement schemes are proposed.The calculation model,corresponding calculation program,extraction characteristic curve,optimization ideas and improvement schemes presented in this paper will provide some theoretical support for the development and application of multi-port compound molecular pump. |
