Patent ID: 6752588
Filing Date: 2004-06-22
Classification: F04D

Abstract:
A vacuum pump comprising:a rotor; a pump case surrounding the rotor; a flange portion formed around the top periphery of the pump case; a plurality of pump fastening holes provided at a periphery of an exhaust port of a vacuum chamber facing the upper surface of the flange portion; a plurality of vacuum chamber fastening bolt-holes (3) provided in the flange portion so as to correspond to the pump fastening holes, said vacuum chamber fastening bolt-holes being passed through with a pump-chamber fastening bolt; a base fastening portion formed around the bottom periphery of the pump case; a base member covering the lower side of rotor and facing the lower surface of the base fastening portion; a plurality of pump case-base member fastening holes provided so as to correspond to the base fastening portion and the base, respectively; and a plurality of pump case-base member fastening bolts for fastening the pump case and the base by inserting and screwing into the pump case-base member fastening holes; wherein the dimensional relationships between the diameter of each bolt-hole and that of the shank of the corresponding bolt satisfy both or either one of the following conditions (a) and (b): (a) a vacuum chamber fastening bolt-hole has a larger diameter than the shank diameter of the corresponding pump-chamber fastening bolt by 20% or more; and (b) a bolt-hole, which is either one of the pump case-base member fastening bolt-holes provided in the base fastening portion and the base, has a larger diameter than the shank diameter of the corresponding pump case-base member fastening bolt by 20% or more.