Patent ID: 6964560
Filing Date: 2005-11-15
Classification: F04C,F05C

Abstract:
1. A vacuum pump, compressing and discharging gas in a direction of a rotor axis by rotation of a pair of screw rotors with a cross section perpendicular to the axis formed with an epitrochoid, an arc and an Archimedean-spiral-like curve, said pair of screw rotors engaged together being supported rotatably in a casing, comprising balance pistons being disposed respectively on shafts of said pair of screw rotors at inlet side of said casing, wherein said balance pistons separate a receiving section at area of the screw rotor and a pressurizing section at area of the balance piston, and a thrust force of the screw rotors at a pressurizing condition is canceled by acting the discharge pressure in the pressurizing section, wherein said each balance piston includes a plurality of plate portions and spaces between respective plate portions, and said plate portions of one balance piston are penetrated rotatably into said spaces of the other balance piston.