| 摘要 |
PURPOSE:To economically operate a compressor, by enabling the maximum flow rate of an intermediate-stage by-pass to be varied depending on the actual state of the operation of the compressor to recover as much motive power as possible. CONSTITUTION:A calculator 16 consists of a differential pressure calculator 16a and a pressure ratio calculator 16b. The differential pressure calculator 16a is provided to detect that the pressure difference between the suction and discharge of a last-stage compressor 1c exceeds a prescribed level. The pressure ratio calculator 16b is provided to predict the temperature of discharge from the pressure ratio to detect that the temperature reaches a critical level. The output signals of the calculators 16a, 16b are applied to a first selector 17. When one of the signals has reached its limit value, the signal is applied to a second selector 18 so that the output signal of a pressure detector 8 is kept in its existing state to fix the degree of opening of a pressure control valve 7. Until the limit- value signal is applied to the second selector 18, the pressure control valve 7 is kept open on the basis of the output signal of the pressure detector 8 to increase the flow rate of a by-pass 6 to its allowable limit. |
