Features and application:  1. Purpose: to change the valve for high-rise building fire system. When the pressure exceeds the feed line relief valve set pressure, pressure relief valve is open, to prevent the pipeline and equipment damage due to overpressure; pressure down to the set value, the valve automatically closes.  2. Features: streamlined body with a full-channel design, fluid resistance, flow rate. The valve can be done to make the pressure relief valve holding pressure valve. Will do when the pressure relief valve water valve in the security settings than the wizard of pressure release, and maintain its value in under pressure in a safe, cause the system to prevent the risk of excessive water pressure; to do when holding pressure valve can be maintained upstream of the main valve at a water pressure above the set value, only the upstream pressure is higher than the set value, only the downstream water supply, to ensure the water supply pressure upstream of the main valve.