Three-screw expander

The invention provides a three-screw expander which comprises a shell. A front end cover and a rear end cover are further arranged at the two ends of the shell. An anode rotor, a first cathode rotor and a second cathode rotor are arranged in the shell, wherein the first cathode rotor and the second cathode rotor are symmetrically distributed on the two sides of the anode rotor and are engaged withthe anode rotor. Two air inlets are formed in the front end cover, and two air outlets are further formed in the rear end cover. The air inlets and the air outlets communicate with air ways, and theair ways communicate with the cathode and anode rotors. The three-screw expander is simple in structure, the anode rotor, the first cathode rotor and the second cathode rotor are arranged in a linearshape so that the radial force exerted on the anode rotor can be balanced, the loaded condition is greatly improved, and the output is stable; noise and vibration are also relatively small, higher input pressure can be borne, t