Watts 0386462 1/2″ dual check valve 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 backflow preventer, model 9d and a bronze feed water pressure regulator, model 1156f, 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 and has 1/2 inch union solder inlet x npt threaded outlet connections. The maximum pressure is 100 psi (6.9 bar).