The basic structure of a screw air compressor is: a pair of intermeshing spiral rotors is arranged in parallel in the compressor body. Usually, the rotors with convex teeth outside the pitch circle are called positive rotors or positive screw, and the rotors with concave teeth in the pitch circle are called the negative rotor or the negative screw. Generally, the positive rotor is connected with the prime mover. The positive rotor drives the last pair of bearings on the negative rotor to realize the axial positioning and bears the axial force in the compressor. The cylindrical roller bearings at both ends of the rotor enable the rotor to be positioned in a radial direction and bear the radial force in the compressor.

When the rotor is driven by the motor, the space of the tooth groove of the master-slave rotor rotates to the opening of the inlet end wall, the outside air fills it. When the end face of the rotor’s inlet side is transferred from the inlet port of the shell, the air between the groove is closed between the main and the slave rotor and the casing to complete the inhalation process. At the end of the inhalation, the closed volume formed by the tooth peak of the main rotor and the slave rotor and the casing decreases with the change of the rotor angle and moves in a spiral shape, which is called “compression process”. When the closed tooth peak of the rotor rotates to meet the exhaust port of the casing, the compressed air begins to be discharged until the coincidence surface of the tooth peak and the tooth groove moves to the exhaust end face. At this time, the space of the tooth groove is zero, which means the exhaust process is completed. At the same time, another pair of tooth grooves of the master-slave rotor has been rotated to the air inlet to form the maximum space and started the suction process, thus starting a new compression cycle.