2-1/2" Backflow Preventer, APOLLO 4ALF20909 Reduced Pressure Principal, Lead-Free with Butterfly Valve Grooved Connections2 1 2" Backflow Preventer, Reduced Pressure Principal, Lead Free , Stainless Steel Body with Butterfly Valves Grooved Connections APOLLO 4ALF20909 DESCRIPTION The Apollo Model RPLF 4A Reduced Pressure Principle Backflow Preventers consist of two independently acting, TriForce center stem guided check valves with a differential pressure relief valve located between the check valves. The unit is designed to give maximum protection against backflow of