10" Backflow Preventer, APOLLO 4ALF20G02 Reduced Pressure Principal, Lead-Free with Flanged NRS Gate Valves10" Backflow Preventer, Reduced Pressure Principal, Lead Free with Flanged Non Rising Stem (NRS) Gate Valves APOLLO 4ALF20G02 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 health