Patent ID: 8366380

Claim:
A turbo-molecular pump comprising: a housing having an intake port and an exhaust port; a rotary body which is enclosed in the housing and has rotor blades of a plurality of stages that are formed so that the outside diameter of at least one stage on the exhaust port side is smaller than that on the intake port side; a rotary shaft pivotally supporting the rotary body; a motor for rotating the rotary shaft; stator blades which are fixed to the housing, being arranged between the rotor blades, and each of which is divided into at least two pieces; and spacer rings each having a ring shape continuous in the circumferential direction which are arranged between the stator blades to hold the stator blades at predetermined intervals, and are formed so that the smallest inside diameter of at least one stage of the spacer rings on the exhaust port side is smaller than the largest outside diameter of the rotor blades; wherein the housing comprises a casing whose inside diameter is constant or whose inside diameter is smaller at the intake port side than at the exhaust port side; and wherein a clearance between the adjacent spacer rings which is formed in an axial direction when the spacer rings are moved to the intake port side is larger than a thickness of the stator blade.