To smoothly restart a compressor by preventing rust in the compressor.
An oil-free screw compressor 10 in which cooling water is normally circulated is provided with an intake throttle valve 72 between an intake port 22 of a compressor body 20 and an intake passage 82 communicating with an intake filter 74 for inducting outside air into its housing 11. The intake passage 82 is connected with one end of a dry air duct 86 at its downstream side to the intake throttle valve 72. The other end of the dry air duct 86 is connected to a dry air supply source 50 which is disposed outside the housing 11 of the compressor 10 for continually discharging dry air. The dry air duct 86 is provided with a switch valve 56 constituted of a solenoid valve adapted to be opened during the standing of the compressor 10 to thereby continuously supply dry air to and circulate cooling water in the compressor during the standing of the compressor.
HARAYAMA TATSUO
TANAKA MASANORI
