Screw groove type vacuum pump, complex vacuum pump and vacuum pump system

摘要

A screw groove-type pump has a rotor member mounted for undergoing rotation, a stator member arranged so as to be coaxial with the rotor member and having a peripheral wall disposed opposite to and spaced-apart from a circumferential wall of the rotor member, an inlet port for introducing gas into a space between the circumferential wall of the rotor member and the peripheral wall of the stator member, and an outlet port for discharging gas introduced into the space between the circumferential wall of the rotor member and the peripheral wall of the stator member. A screw groove is formed on one of the circumferential wall of the rotor member and the peripheral wall of the stator member for transferring gas introduced into the inlet port through the space between the circumferential wall of the rotor member and the peripheral wall of the stator member and to the outlet port during rotation of the rotor member. The depth of the screw groove at a point thereof which is nearest the inlet port is equal to or larger than ¼ the diameter of one of the circumferential wall of the rotor member and the peripheral wall of the stator member. An angle of elevation of the screw groove with respect to a radial axis of the rotor member decreases toward the outlet port from the inlet port.