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.

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The drag coefficients of single gas bubbles rising In hydraulic fluids of different kinds are presented. Tests are per formed over the bubble Reynolds number range of 5 ×10^-5 to 10, and the following conclusions are obtained:
(1) The relation between the Reynolds number Re and the bubble drag coefficient Cd in three kinds of anti-wear type oils on the market are in good agreement with Stokes' equation except for bubbles in Re ranges greater than about 6×10^-2.
(2) The values of Cd in high viscosity index hydraulic oils are somewhat larger than those obtained by Stokes' equation, and those in both a water-glycol and phosphate ester are equal to those obtained by the equation.
(3) The R_e C_d relations for four kinds of base oils having different viscosity are very nearly the same as fiadamard Rybczynski's equation except for small bubbles less than about 0.4mm in diameter.
(4) If very small quantities of silicon type deforming agent are added in the base oil, the values of C_d increase Considerably. The addition of large quantities of polymetacrylate type viscosity index improver to the base oil also causes an increase in C_d. The additions of iso-butylen type viscosity index improver, alcohol type deforming agent and rust inhibitors have no effect on the drag coefficients.
(5) The drag coefficient is little influenced by the addition of A. C. Fine Test Dust.

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