the Apollo model RPLF 4A lead free 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 hazard fluids by either back-pressure or back-siphonage. the durable domestic stainless steel units (2-1/2''''-8'''') and the FDA epoxy coated ductile iron units (10'''' and 12'''') are easily maintained in the line without any special tools. the TriForce check valves operate with a spring assist in the flowing condition to provide excellent flow rates which are documented by an independent laboratory.domestic stainless steel body: 2-1/2'''' - 8''''FDA epoxy coated ductile iron body: 10'''' and 12''''easy maintenance - no special tools requiredsnap-in check retainers: 2-1/2'''' - 6''''bolted-in checks: 8'''' - 12''''low pressure loss as documented by an independent laboratorycenter-stem guided triforce check valvesapproved for horizontal flowUS Patents: 6,443,184; 7,025,085; 7,533,699; 8,240,333made in the USA - requires D option5 year warranty