A design method for improving the flow characteristics of a multistage Roots pumps

Based on an analysis of a three-stage design with varying phase angles, this paper proposes a method for improving pump performance in multistage Roots pumps by employing designs that achieve the greatest economy in outlet discharge enhancement. The flow characteristics of multistage Roots pumps with serial and parallel connections are investigated by considering various phase angles in each stage using a two-lobed rotor as an example. The benefits of these varying phase angle designs for both serial and parallel connection pumps are evaluated by comparing their flow characteristic with those of same phase angle designs in 24 different cases. An additional comparative analysis of four-stage serial and parallel connections clearly indicates that multistage Roots pumps with a parallel connection and varied phase angle design is a better choice for vacuum system use.