Patent ID: 7686600

Claim:
A vacuum pump comprising: a pair of screw rotors each having a substantially hollow-cylindrical shape with one site closed and rotating about substantially parallel two axes, respectively; a pair of shafts attached to inside surfaces of the closed portions of said screw rotors so as to extend along said axes, respectively; a pair of bearing members each having a substantially hollow-cylindrical shape and disposed between inner circumferential surfaces of said screw rotors and outer circumferential surfaces of said shafts, respectively, said bearing members having bearings at inner circumferential surfaces thereof, respectively, said bearing members supporting said screw rotors with permitting rotations of said screw rotors about said axes, respectively; and a shaft seal structure structured between the outer circumferential surfaces of said bearing members and the inner circumferential surfaces of said screw rotors; wherein said shaft seal structure comprises a substantially hollow-cylindrical shaft seal members circumferentially attached to said other circumferential surfaces of said bearing members, each of said shaft seal members being porous; and wherein a seal gas is introduced to gaps between said outer circumferential surfaces of said bearing members and inner circumferential surfaces of said screw rotors from overall of outer circumferential surfaces of said shaft seal member, respectively; thereby said shaft seal structure forms a static pressure seal so that said screw rotors are centered with respect to said axes without runout and a contact of said inner circumferential surfaces thereof with said shaft seal members, respectively.