Patent ID: 6461112
Filing Date: 2002-10-08
Classification: F04C

Abstract:
A screw compression apparatus comprising: a screw compressor including a pair of female and male rotors; a motor, controlled by an inverter, for driving the compressor; pressure detecting means for detecting a pressure of an operation gas discharged from said screw compressor; and an air release valve for performing a control to release the operation gas compressed by said compressor to the atmosphere,said apparatus further comprising control means for controlling said motor and said air release valve, wherein the control means controls a rotation frequency of the motor by said inverter at an operation point at which a ratio of an air consumption on a demand side to a compressor rated discharge amount is larger than a predetermined set value, holds the rotation frequency of the motor at a constant value when the ratio indicates said set value or less, controls said air release valve to release the operation gas to the atmosphere after the pressure detected by said pressure detecting means reaches a set upper-limit pressure, and further lowers the rotation frequency of said motor after the pressure of the operation gas reaches an upper-limit pressure.