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" & 12". Easy maintenance - no special tools required. Snap-in check retainers: 2-1/2" - 6". Bolted-in checks: 8" - 12". Low pressure loss as documented by an independent laboratory. Center-stem guided TriForce™ check valves. Approved for horizontal flow. US Patents: 6,443,184; 7,025,085; 7,533,699; 8,240,333. Made in the USA. Requires D option. 5 year warranty.