PERFORMANCE STUDY ON ROTOR PROFILE OF SOME DRY SCREW VACUUM PUMPS

Four kinds of rotor profile performances of dry screw vacuum pumps are compared,which are the profile of double sides and symmetrical circle,si ngle-thread and variable pitch trapezium,constant-pitch trapezium and const ant-pitch concave tooth.The performances include the equations of profile,co efficient of used area,geometric pumping speed and machining,etc.The important variables in the formulas of geometric pumping speed and coefficient of used area are discussed.It draws the conclusion that λ（slenderness ratio of double sides and symmetrical circle profile） is 1～2,ρ（boss ratio of single-thread screw profiles） is 0.30～0.45 andξ（ratio of lead and external diameter） is close to 1.With the same rotor geometric parameters,single-thread and consta nt-pitch concave tooth profile sucks more gas than the two other single-thre ad profiles.