3/4" Backflow Preventer, Reduced Pressure, Lead-Free Bronze with Ball Valves and SAE Test Cocks APOLLO 4ALF204A2F3 4" Backflow Preventer, Reduced Pressure, Lead Free Bronze with Ball Valves and SAE Test Cocks APOLLO 4ALF204A2F DESCRIPTION The Apollo Model RPLF4A Series Reduced Pressure Backflow Preventers provide maximum protection against back siphonage or backpressure from substances that are hazardous to the potable water supply. The top accessed modular check valve cartridges provide captured springs, replaceable seats and reversible silicone seat discs.