500X pressure relief / holding pressure valve is mainly used for fire protection or other water supply systems to prevent systems over pressure or maintain the water supply pressure of fire protection system. Closing of the fire protection pumps can reduce the impact of water hammer. The valve is also used for eliminating water hammer devices of large-scale water supply system. What's more, at the inlet of valve control system is a self-cleaning filter which makes suspended particles with larger proportion and diameter not enter the control system by using characteristic of flow to ensure smooth system circulation so that the valve can operate safely and reliably. It has stable system operation, high strength, long service life. The valve   is applicable to pipelines of less than DN600mm.