Due to uncertainty and assumptions during hydraulics design of any process unit, Pumps and Compressors are normally sized with average of 20% over-design capacity. it is of the good engineering practice to revisit the pump design assumptions and size selection to evaluate compatibility to system requirement.
Controlling pump discharge flow or head is normally done via throttling the control valve downstream the pump which result in power losses on the motor and erosion damage on the valve.
Variable Speed Drives (VSD) is a more efficient solution to control both flow and discharge pressure of a pump or compressor. Decreasing the pump speed will decrease the discharge pressure and hence the flow as per the famous “Pump Affinity Law”.