This 1/2 inch 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 1/2 inch union NPT inlet x NPT theaded outlet connections. The maximum pressure is 100 psi