Which control device varies the speed of the pump motor?

• A. Flow & Pressure Start
• B. Variable Frequency Drive
• C. Pump Start Relay
• D. Integration with irrigation controls

Answer: (B)

Varying the speed of a pump motor is done by a device that can adjust the electrical supply to the motor in real time. A Variable Frequency Drive changes both the frequency and voltage of the power going to the pump, which changes the motor’s RPM and allows the system to match pumping to demand, saving energy and reducing wear. Flow & pressure start devices are used to start and stop the pump based on sensed flow or pressure; they don’t modulate speed. A pump start relay simply switches the motor on or off with no speed control. Integration with irrigation controls refers to communication with controllers, not speed modulation. So the device that actually varies the pump speed is the Variable Frequency Drive.