AX742X security holding pressure/pressure relief valve installed in high-rise buildings, fire water system and other water supply pipeline, when the pressure in feed line more than pressure relief valve set pressure, the pressure relief valve open automatically rapid pressure release, to protect the safety of pipeline, also can be used for holding pressure valve, the main valve upstream of the water supply pressure. The safety setting pressure can be maintained accurately, once the pressure is over, the relief valve is opened quickly and the pressure is in time. Close stable and reliable, eliminate the pressure residue.