Abstract: Described herein is a method for operating an oil-free screw compressor and an oil-free screw compressor construction, the method including the step of feeding a gas of a temperature Ta to a discharge space in the vicinity of the discharge port of the compressor, the temperature Ta satisfying the relationshipTa.ltoreq.Tl/kwherein Ta is the temperature (.degree.K.) of said feed gas; Tl is the temperature (.degree.K.) of the compressed gas before feeding; and k is a polytropic index number.

Abstract: A screw vacuum pump which includes a casing having a rotor chamber opened at its one end to a suction opening and opened at the other end to a discharge opening; a pair of male and female screw rotors rotatably received in the rotor chamber, each of the screw rotors having a pair of rotor shafts supported by forcibly lubricated bearings on both sides of the suction opening and the discharge opening; at least one first sealing member provided between the bearing on at least the suction opening side and the rotor chamber and communicated with a space under pressure less than atmospheric pressure which space is out of communication with the suction opening; and at least one second sealing member provided between the bearing on at least the suction opening side and the rotor chamber and communicated with the atmosphere, the first and second sealing members being arranged in this order from the rotor chamber side.