Abstract: The invention relates to a capacity control method for controlling the capacity of a multistage compressor in response to a flow rate signal by varying the openings of vanes at individual stages. The relationships of the openings of the vanes of the individual stages are made to vary in response to the flow rate signal from the multistage compressor. Thus, when the flow rate of the multistage compressor is far from the anti-surge capacity within the operable range thereof, it is possible to select vane opening relationships which provide the highest efficiency for the multistage compressor. When the flow rate of the multistage compressor drops to either a value near the anti-surge capacity or the inoperable range, on the other hand, it is possible to select vane opening relationships which provide an enlargement of the operating range of the multistage compressor, before the flow rate enters that inoperable range.

Abstract: A method of controlling the operation of multistage centrifugal compressor equipment provided with inlet guide vanes and diffuser vanes at each stage to enable operation to be practiced at a low energy consumption level. The method includes the steps of determining whether the prevailing flow rate, for example, is in a range of flow rates near the desired flow rate or in a range of flow rates remote therefrom; and controlling a combination of the amount of operation of the guide vanes with the amount of operation of the diffuser vanes, which is set beforehand, when the prevailing flow rate is determined to be in the latter range to promptly bring the prevailing flow rate to the desired flow rate level, and effecting fine adjustments of the inlet guide vanes and diffuser vanes to control the angles thereof when the prevailing flow rate is determined to be in the former range, thereby enabling increased efficiency to be achieved in the operation of the compressor equipment.