Patent ID: 8622725

Claim:
A screw compressor, in which a pair of intermeshing male and female screw rotors are housed in a rotor chamber formed in a casing, and a gas sucked from an intake channel is compressed by the screw rotors and discharged from a discharge channel, the screw compressor comprising: a columnar space including a functional end face having an opening into an intermediate pressure section, which is an empty space in the rotor chamber and is isolatable from both the intake channel and the discharge channel by the screw rotors, and an opening into a bypass channel which communicates with the discharge channel; a piston fittingly inserted in said columnar space such that when said piston is brought into contact with said functional end face, said piston separates said intermediate pressure section from said bypass channel; and a pressure detection channel that allows an area located on an opposite side of said functional end face across said piston in said columnar space to communicate with the discharge channel, wherein, when a pressure of the intermediate pressure section is lower than a pressure of the discharge channel, the piston is brought into contact with the functional end face by a pressure difference between a side of the piston adjacent the functional end face and the opposite side of said functional end face across the piston in the columnar space, thereby isolating the bypass channel from the rotor chamber, and wherein, when the pressure of the intermediate pressure section is higher than the pressure of the discharge channel, the piston moves away from the functional end face by the pressure difference, thereby causing gas to flow into the discharge channel from the intermediate pressure section via the bypass channel.