The Hersey 6CM RPDA is a reduced pressure detector assembly (RPDA). It was available in 4″-10″ sizes and was produced from 1991-2004. The body was made of either bronze., galvanized cast iron, or epoxy coated cast iron. The repair parts are different for the bronze. and cast iron models. The 6CM RPDA utilizes a 1 1/2″ FRPII for the bypass assembly.