Gas compressor

A gas compressor comprising:

• a compressor main unit that compresses a gas;
• a drive source that drives the compressor main unit;
• an intake throttle valve that adjusts an amount of gas intake of the compressor main unit;
• a gas release valve that releases a discharged gas of the compressor main unit to an atmospheric pressure environment;
• rotation speed converting means that changes a rotation speed of the drive source;
• a pressure detecting device that detects a discharge pressure of a discharged gas system, wherein H is an upper-limit pressure and L is a lower-limit pressure and H>L;
• and
• a controller that carries out opening the intake throttle valve and closing the gas release valve and operating the drive source at a full-load rotation speed until the discharge pressure reaches the upper-limit pressure H, and carries out at least one of closing the intake throttle valve and opening the gas release valve to reduce the discharge pressure when the discharge pressure reaches the upper-limit pressure H, and carries out switching to a different mode when the discharge pressure drops to the lower-limit pressure L, wherein
• the controller outputs a command of a lower rotation speed than the full-load rotation speed to the rotation speed converting means when the discharge pressure rises and reaches the upper-limit pressure H,
• the controller outputs a command of the full-load rotation speed to the rotation speed converting means when the discharge pressure drops and reaches the lower-limit pressure L, and
• the gas compressor includes an end pressure detecting device that detects a pressure of an external piping system that connects to the discharged gas system, wherein
• the controller carries out opening-closing operation of at least one of the intake throttle valve and the gas release valve and outputs a command of the lower rotation speed and a command of the full-load rotation speed to the rotation speed converting means according to pressures obtained by subtracting a pressure loss of the external piping system based on a detected pressure of the end pressure detecting device from the upper-limit pressure H and the lower-limit pressure L.