SCREW VACUUM PUMP

PURPOSE:To improve pumping speed and obtain clean vacuum with high reliability by forming an inlet at the center part of a casing as well as discharge openings at both sides of operating chambers formed of two sets of screw rotors provided in the bilateral axial direction. CONSTITUTION:When one of axis of rotation 9a, 9b is rotated, bilateral screw rotors 4a, 4c and bilateral screw rotors 4b, 4d are rotated in the mutually opposite direction through timing gears 12a, 12b. Gas is inhaled from an inlet accompanied by this rotation, and the gas inhaled into an operating chamber 5a formed of the bilateral screw rotors 4a, 4c is discharged from a first discharge opening 7a provided at the terminus of the operating chamber 5a and the gas inhaled into an operating chamber 5b formed of the bilateral rotors 4b, 4d from a first discharge opening 7b at the terminus of the operating chamber 5b respectively. The gas discharged from the respective first discharge openings 7a, 7b is mixed at the center of a main casing and discharged outside from a second discharge opening.