Inner pressure measurement of turbo molecular pump

Abstract

The pressure of the gas including free molecular, transition, slip, and continuum flow inside the turbo booster pump is successfully measured in this study. This pump was developed through the cooperation of Kashiyama Industries Ltd. and Precision Instrument Development Center, with the goal of replacing the mechanical booster pump. The flow-meter method of Japan’s standard JVIS-005 is adopted here to simulate the operating condition of the pump in different pressure ranges. The laboratory and the experimental apparatus are constructed according to the International Standards Organization and JVIS standards. In order to measure the pressure variations from the pump inlet to the outlet, nine holes with 6.5 mm inner diameter are drilled through the pump casing around the periphery along the axial direction. The distances of these holes from the plane of the inlet port are 49.5, 79.5, 107, 127, 147, 167, 187, 207, and 227 mm. The metal gasket face seal fittings with inner diameter 3 mm are welded into the holes using the TIG-tungsten inert gas welding method. The metal bellow tube is used to link the vacuum gauges and the metal gasket face seal fittings. The accuracy range of the vacuum gauges is 1.33×10−4–133 mbar. Six cases of the pump inner pressure with the pump inlet pressure 1.33×10−4, 1.33×10−3, 1.33×10−2, 0.133, 0.665, and 1.33 mbar are performed. The pressure variations along the axial direction are plotted. The pressure trend related to the rotor shape is discussed. The pressure discrepancies between the measured and calculated done by the Computational fluid dynamics method are compared.