Design methodology and performance analysis of self-balancing screw rotor for dry screw vacuum pumps

The self-balancing screw rotor represents an advanced structural configuration for dry screw vacuum pumps. This study systematically extends the design methodology of self-balancing screw rotors and proposes a novel approach to enhance their design flexibility. The performance characteristics of self-balancing rotors are comprehensively analyzed from the perspectives of geometry and thermodynamics. A mathematical model for the balance calculation of screw rotors is established, and various self-balancing methods are compared to demonstrate the superior design flexibility of the proposed method. Subsequently, a simulation model is constructed to reveal the differences in performance between conventional variable-pitch rotors and self-balancing rotors. Critical design parameters (volume index and number of stages) of self-balancing rotors are discussed in the context of design constraints and their impacts on performance. Compared with the conventional triple-section variable-pitch rotor, the self-balancing rotor reduces the rotor length from 451 to 296 mm, the power consumption under ultimate vacuum conditions from 1.83 to 1.52 kW, and the outlet temperature from 143 to 131 °C. Its specific pumping speed is 12% higher in the medium-vacuum region, although this advantage decreases in the low- and high-vacuum regions. The feasible range of maximum and minimum volume indexes for self-balancing rotors is determined by the minimum pitch permissible for machining. Increasing the volume index can significantly improve the specific pumping speed of self-balancing rotors in the medium-vacuum region, while increasing the number of rotor stages improves the overall performance of screw rotors. The conclusions derived from this study can provide valuable guidance for the design of self-balancing rotors in dry screw vacuum pumps.