Patent ID: 8257053

Claim:
A compressed air manufacturing facility, comprising: a compressor configured to compress air; a discharge air system connected to a discharge side of said compressor; an electric motor configured to drive said compressor; an inverter configured to variably control a rotating speed of said electric motor; a pressure detecting means configured to detect the discharge pressure of said compressor at the upstream side position of said discharge air system; a control apparatus configured to: compute a pressure loss of said discharge air system, the pressure loss being a difference of the discharge pressure of said compressor at the upstream side position of said discharge air system as detected by said pressure detecting means, to a pressure at a downstream side position of said discharge air system, in correspondence to the rotating speed of said electric motor, change a control range of a discharge pressure of said compressor at an upstream side position of said discharge air system, on the basis of the pressure loss computation, in such a manner that a terminal pressure at a downstream side position of said discharge air system falls within a predetermined range, variably control the rotating speed of said electric motor via said inverter such that the discharge pressure of said compressor, as detected by said pressure detecting means, falls within the control range changed by said control apparatus, switch the compressor to an unload operation, when the discharge pressure of the compressor increases up to an unload start pressure, as detected by the pressure detecting means, during a load operation of the compressor, switch the compressor to a load operation, when the discharge pressure of the compressor decreases down to a load return pressure, as detected by the pressure detecting means, during an unload operation of the compressor, and change the unload start pressure and the load return pressure, such that a terminal pressure of an air discharge system falls within a predetermined range, on the basis of a pressure loss of the discharge air system as computed in correspondence to the rotating speed of said electric motor.