Shaft seal structure for vacuum pump

Abstract

A vacuum pump has a housing accommodating a rotary shaft and a gas transferring assembly driven by the rotary shaft. The housing has an exhaust passage for exhausting gas outside the housing. The gas transferring assembly creates a vacuum. A lip seal for shaft seal is disposed between a pump chamber communicating with the exhaust passage and a region in which oil exists so as to slide relative to a circumferential surface of the rotary shaft. The lip seal has a back pressure surface in a back pressure region facing the pump chamber and a pressure surface facing the region in which the oil exists. A communicating passage in the housing intercommunicates the back pressure region and the exhaust passage for applying at least substantially the pressure in the exhaust passage to the back pressure surface.

Dependencies are inferred from the claim text.