Experimental Research on the Variable-speed Operating Characteristics of a Dry Multistage Roots Vacuum Pump

To investigate the effects of rotational speed on the operating characteristics of a dry multistage Roots vacuum pump, an experimental test rig for a six-stage Roots vacuum pump was established. Temperature, pressure, volumetric flow rate, and electrical power were measured at different rotational speeds. A gas resistance torque model was employed to calculate the gas compression power of each stage. The thermal, pumping, and power characteristics were analyzed under zero-flow startup, zero-flow ultimate-pressure, and variable-flow steady-state conditions. The results show that the interstage pressures exhibit a stepwise distribution, while the casing outer-wall temperature is distributed nonuniformly. The maximum temperature is consistently located on the outer wall of the high-pressure sixth stage. As the rotational speed increased from 2700 to 5100 r·min⁻¹, the ultimate inlet pressure after thermal stabilization decreased from 10.36 to 0.04 Pa. At 5100 r·min⁻¹, the maximum casing outer-wall temperature was 66.2℃. The fifth and sixth stages together accounted for 94.33% of the total gas compression power, while the total gas compression power accounted for 35.6% of the motor input power. At all tested rotational speeds, the volumetric flow rate and volumetric efficiency first increased and then decreased with increasing inlet pressure, with their peaks occurring at approximately 200 Pa. At 5100 r·min⁻¹, the maximum volumetric flow rate and volumetric efficiency reached 483.93 L·min⁻¹ and 79.97%, respectively. The volumetric flow rate remained relatively high over the inlet pressure range of 100–1000 Pa. These results clarify the effects of rotational speed on the interstage pressure distribution, temperature distribution, power distribution, and pumping performance of a dry multistage Roots vacuum pump, and provide an experimental basis for variable-speed design and performance optimization.