Patent ID: 8790100

Claim:
A screw expander, comprising: a casing; an intake flow path provided in said casing; an exhaust flow path provided in said casing; a pair of male and female screw rotors housed in a rotor chamber formed in said casing and engaged with each other, said screw rotors converting an expansion force of a high-pressure gas supplied from said intake flow path to said rotor chamber into a rotational force and exhausting a low-pressure gas after expansion to said exhaust flow path; a bypass flow path provided in said casing and communicating with said intake flow path; a valve mechanism capable of selectively allowing communication between an intermediate pressure portion, which is a space in said rotor chamber that can be separated from said intake flow path and said exhaust flow path by said screw rotors, and said bypass flow path; an intake pressure detector for detecting a pressure in said intake flow path; an exhaust pressure detector for detecting a pressure in said exhaust flow path; and a controller for controlling said valve mechanism in accordance with an operation expansion ratio, which is a ratio of the pressure in said intake flow path detected by said intake pressure detector to the pressure in said exhaust flow path detected by said exhaust pressure detector.