Pressure sustaining valve

A pressure sustaining valve senses upstream pressure and modulates to preserve a required minimum pressure on its inlet side. When upstream pressure falls below the setting, it moves toward closed and restricts downstream demand; as pressure recovers, it can reopen. This differs from a pressure reducing valve, which controls downstream pressure, and from a relief valve that discharges fluid to protect against overpressure. Selection should consider the sensing point, downstream flow demand, modulation range, stability, and the valve's effect on the protected upstream zone.