This 1/2" bronze combination fill valve and backflow preventer is for use in commercial and residential hydronic heating systems to provide make-up water to the boiler, and prevent backflow when supply pressure falls below system pressure. It consists of a bronze model 9D backflow preventer and a bronze feed model BD1156F water pressure regulator in one pre-assembled unit. The high capacity fill valve provides quick system filling and purging. It is designed for use in the boiler feed lines of hydronic heating systems. It has BSP threaded connections. The maximum pressure is 100 psi (6.9 bar).