Saving Energy in Existing Hydraulic Systems

The pumping power lost across a control valve is approximately  

A = pressure drop, psi GPM = (U.S.) gallons per minute s.g. = specific gravity 

Installation only of a larger control valve, or larger valve trim, will save zero energy regardless of the result of the above calculation. In addition to modification of the control valve, the upstream centrifugal pump must also be modified. Assuming that the pump is driven by a fixed speed AC motor, the size of the pump s impeller has to be reduced. The smaller impeller plus the larger control valve will result in  

The pump vendor publishes a family of curves for different size impellers. Using the rules described in this chapter, you can select an energy efficient combination of a new pump impeller and a new or modified control valve. 

The size of the motor is not insignificant. The power required to run a motor depends on what it is driving, not on the horsepower rating of the motor itself. 

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