AX742X pressure discharging/retaining valve is mounted on the pipeline of high buildings¡¯, fire fighting and other water supply systems. The pressure discharging valve will automatically open to quickly discharge the pressure when the pressure inside of the pipeline surpass the set one so as to protect the pipeline¡¯s safety. It can also be used as a pressure retaining valve to guarantee the water supply pressure of the main valve¡¯s upper-streamline.