VACUUM PUMP

PURPOSE:To enable the operation, in always and respectively stable conditions, of all impellers by supporting each stage impeller with spiral groove radial and thrust bearings supplied with gas for generating dynamic pressure. CONSTITUTION:Plural stages of turbo-impellers 19, 20 and vortex pump impellers 21 to 24 are supported independently every impeller group to each other and rotatably in casing elements 3 to 6 through radial dynamic pressure bearings formed by spiral grooves 47 to 51 provided respectively on a shaft 18. Between respective both end faces, perpendicular to the shaft, of each impeller group and the side face of a cap 60 fixed against the element 3 to 6 respectively facing to the both end faces in axial direction, thrust dynamic pressure bearings are also provided, which are formed by thrust collars 61 to 70 made of seramic provided with spiral grooves respectively. Respective stage impeller groups thereby can take an optinal rotating speed respectively and a stable operation becomes possible without allowing a motor to continuously run under an abnormal overload.