A pressure sustaining valve maintains a minimum set pressure upstream of the valve. The valve is controlled by a pilot which can be set to the desired pressure. The pilot senses the upstream pressure causing the valve to gradually close if the pressure is below the set point or gradually open if the pressure is above the set point. Pressure sustaining valves can be remotely operated with an addition of a solenoid, hydraulic relay or a shuttle valve.

Pressure sustaining valves are used to maintain a minimum upstream pressure. They are typically used to maintain a minimum pressure on pumps during pipeline fill up or a minimum pressure for consumers or applications upstream.