Patent ID: 7500838

Claim:
A vacuum pump comprising a pair of screw rotors having a first screw rotor with a plurality of helical land portions and a second screw rotor with a plurality of helical groove portions and adapted to rotate about two axes substantially parallel to each other while engagement with each other, a casing receiving therein said pair of screw rotors, and a pair of bearings provided on a pair of shafts supporting said pair of screw rotors, said vacuum pump characterized in that a pair of shaft seals are provided between said pair of screw rotors and said pair of bearings so as not to be in contact with said pair of shafts during steadiness operation, said pair of shaft seals are each a static pressure shaft seal, and a seal gas is introduced between said shaft seals and said shafts through portions of said shaft seals, and that said pair of shaft seals comprise a pair of shaft seal members provided between said pair of screw rotors and said pair of bearings so as not to be in contact with said pair of shafts during the steadiness operation, a tapered surface is formed inside each of said pair of shaft seal members so as to taper off as going away from the corresponding screw rotor, and bearing housings are formed each on a bearing side with respect to the corresponding shaft seal member.