Groundwater is pumped and supplied downwards to a water treatment plant. In case of pump failure, the pressure drops immediately and due to gravity, the water will flow downwards to the plant. As the gravity pipeline is emptied, there will be a vacuum potentially causing pipe collapse and contamination of the water in the pipe system from the surroundings.
A pressure sustaining control valve (PSV) installed close to the pipe entrance at the water plant senses inlet pressure, and if this drops below a specified setpoint due to pump stop, the valve will close drip tight in order to maintain positive pressure in the pipe, thus avoiding the risk of vacuum conditions. When the pump starts and the inlet pressure is again above the setpoint, the valve will open and the water supply to the plant will continue.