べ一ン型真空ポンプの吸排気時期について

Abstract

Rotary-vane vaccum pumps are used not only at a high vacuum but also at a medium vacuum. For example, pumps which are used for automation systems including a vacuum lift, or for vacuum boost brakes of motor trucks and so on, are operated at a medium vacuum in a steady state or varying from high to medium vacuum. In this paper, we studied the influence of the port timing of the pump onto t h e value of the torque for transportation of air (air pressure torque), during pump operation from a high vacuum to atomospheric pressure. For reciprocating or rolling-piston type cavuum pumps ect., the thermodynamic cycle is relatively simple, and so the work of such a cycle coincides with the technical work during the process of adiabatic compression, but for usual rotaryvane vacuum pumps, the cycle is more complicated, because there are some problems owing to over-compression or undercompression. We assumed an ideal cycle for a rotary-vane vacuum pump. Comparing the assumed cycle with the actual cycle obtained from the indicator diagram of the actual pump, we examined the propriety of the assumption, and found that the assumption is approximately reasonable. Further, analyzing the ideal cycle, we investigated the effect of the port timing which has an influence upon the air pressure torque, and clarified the design factors for selecting of the port timing corresponding to various suction pressures in order to reduce the air pressure torque.