Patent ID: 8246300

Claim:
A vacuum pump, comprising a cylindrical pump case, a rotor rotatably provided within a cylinder of the pump case, a plurality of rotor blade wheels formed in a multi-stage manner on an outer circumference of the rotor, a plurality of stator blade wheels provided within the cylinder of the pump case and arranged alternately with the rotor blade wheels in a multi-stage manner with a prescribed gap from the rotor blade wheels, and a plurality of ring spacers that are provided within the cylinder of the pump case and are each interposed between the stator blade wheels, wherein each of the rotor blade wheels is provided with upper and lower rotor-blade end faces, each of the stator blade wheels consists of a pair of cut-off half-annular stator blade wheels and has a blade part and an outer ring part, the blade part is provided with upper and lower stator-blade end faces, each of which facing to a corresponding one of the rotor-blade end faces, the outer ring part is provided with upper and lower base end faces, each of which abutting against a corresponding one of cylindrical abutment end faces of the ring spacers and having a level difference from a blade-part end face of the stator blade wheel, characterized in that the distance between the base end face of the outer ring part and a supposed plane which includes the rotor-blade end face corresponding to and substantially parallel with the base end face of the outer ring part is set at a value larger than the range of deformation of the rotor blade wheel during pump operation.