Variable Speed Pumps

These pumps are called Variable Speed Drive Pressure Pumps "Constant Pressure Pumps". As you turn taps on and off, the motor speed adjusts accordingly giving you constant pressure. The pump controller adjusts the motor speed and maintains constant outlet pressure, even with fluctuating demand.

Variable frequency drives are used for adjusting flow or pressure to the actual demand. They control the frequency of the electrical power supplied to pumps or fans. Significant power savings can be achieved when using a VFD pump. 

A variable frequency drive is a system for controlling the rotational speed of an alternating current electric motor. It controls the frequency of the electrical power supplied to the motor. A variable frequency drive is a specific type of adjustable-speed drive. Variable frequency drives are also known as adjustable frequency drives (AFD), variable speed drives (VSD), AC drives, or inverter drives. 

Automatic frequency control consists of a primary electrical circuit converting the alternating current into a direct current, then converting it back into an alternating current with the required frequency. Internal energy loss in the automatic frequency control is rated ~3.5 % 

Variable frequency drives are widely used on pumps and machine tool drives, compressors and in ventilations systems for large buildings. Variable frequency drive motors on fans save energy by allowing the volume of air moved to match the system demand. Reasons for employing automatic frequency control can both be related to the functionality of the application and for saving energy. For example, automatic frequency control is used in pump applications where the flow is matched either to volume or pressure. The pump adjusts its revolutions to a given setpoint via a regulating loop. Adjusting the flow or pressure to the actual demand reduces power consumption.