The pressure-maintaining pressure relief valve consists of a main valve and an external control pilot valve. It is mainly installed in the bypass of the protected water supply system of the building to ensure the pressure of the water supply area upstream of the main valve. When the pressure in the water supply pipe exceeds the set pressure of the pressure relief valve, the pressure relief valve opens to prevent pipelines and equipment from being damaged due to overpressure. damage. This valve is mainly used for pressure relief in the fire test circulation system of high-rise buildings. It is an upgraded product of the spring-type safety valve.