The 500X pressure release/maintenance valve is mainly used in fire fighting or other water supply systems to prevent the occurrence of overpressure or maintain the pressure of a fire fighting water supply system. After the fire pump is shut down, the valve can also serve to reduce the impact caused by water hammer. It can also be used as the water hammer eliminating device in large water supply systems; as a self-cleaning screen is installed at the inlet of the valve control system, suspended particles of relatively big specific gravities and diameters will not enter the control system because of the fluid characteristics of these particles, which guarantees the smooth and unobstructed circulation of the system, thereby ensuring the safe and reliable operation of the valve. With the help of the valve, the system is able to operate smoothly, high in strength and long in service life. It is suitablefor use with pipes of a caliber below 600.