The Caleffi 573009A is a 1/2-inch sweat automatic filling valve with a 1/2-inch NPT connection, designed for incorporation into hydronic heating systems such as boilers and radiant heating setups. By preventing overfilling and automatically replacing water as needed, this valve plays a crucial role in ensuring that the system's water level stays at the proper level. #Caleffi #57300... https://www.partshnc.com/573009a-caleffi-12-swt-bfpautofill-12-npt