Q: What is the most common control strategy employed in pump operation? A: Sometimes, pumps are designed to operate in a wide range of flow rates. Therefore, the pump should be able to ramp up and down depending upon flow requirements. Motors powering these pumping plants are usually single speed, which means that pumps are also restricted to a single speed and cannot ramp up or down depending upon flow requirements. In such situations, the pump discharge is throttled to reduce pump discharge rate. Throttling is a very inefficient means of controlling flow rate. Motors can be retrofitted with Variable Frequency Drives (VFD) to vary motor speed. By changing motor speed, pump speed can be varied. Pump discharge rate is directly proportional to the operational speed.