2-1/2" Backflow Preventer, APOLLO 4ALF20903 Reduced Pressure Principal, Lead-Free with Flanged OS&Y Gate Valves2 1 2" Backflow Preventer, Reduced Pressure Principal, Lead Free , Stainless Steel Body with Flanged OS&Y Gate Valves APOLLO 4ALF20903 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 health or non