The GPE unit is designed to work with one pump controlled by a frequency converter VLT (inverter) whilst the others are triggered directly. The thus-configured unit can be used to keep pressure in the water main constant. As mains pressure varies, the pump controlled by the VLT (inverter) varies its speed of rotation to restore pressure to the set value. If the amount of water being drawn exceeds the pump’s capacity, the second pump is triggered directly and, at the same time, the VLT-governed pump enters control mode to keep water pressure at the set value. The same goes for all the unit’s component pumps. When drawing has stopped, the VLT-governed pump reaches minimum rotation value and then stops after a few minutes, making for considerable energy savings.