Pressure sustaining control valve is hydraulic control valve designed to protect the system by rapidly discharging the high pressure wave by sudden opening movement in water systems with excessive pressure increase. With the pilot on the valve, the input pressureis adjusted with the desired pressure. If for any reason the inletpressure in the system rises above the set value, the valve is opened quickly to release excess pressure to the outside and the system is protected. Despite its sudden opening, due to the hydraulic principle of operation, the closing of the valve is slowed down so as not to create a ripple. It provides a completaly leak-tight seal. It can also be used as a safety and warning valve at the exit points of the pressure reducing control valves alone at critical points in the water system.