This valve is used in the fire protection system of high-rise buildings. When the pressure in the water supply pipeline exceeds the set pressure, the pressure relief valve opens to prevent damage to the pipeline and equipment due to overpressure; When the pressure drops to the set value, the valve automatically closes. 
Features: 
The pressure in the water supply pipe that exceeds the safety setting value of the pilot valve can be released, and the pressure in the pipe can be maintained below the safety value to prevent system hazards caused by excessive water pressure. 
Principle: 
The inlet side of the main valve is connected to the pilot valve through a control pipe. When the pressure on the inlet side exceeds the set pressure of the pilot valve, the pilot valve opens to release the pressure in the upper chamber, and the main valve disc opens accordingly. The main valve maintains pressure, and when the pressure drops to the set pressure, the pilot valve closes and the main valve also closes.