The RP-500 Backflow Preventer is designed to supply maximum protection against back flow caused by negative pressure or backpressure. Backflow may cause infiltration of chemicals, fertilizers and/or other pollutants into potable water systems. The RP-500 is reliable and easily maintained, without the need for special tools. The RP-500 is built with two independent, easily replaceable capsulated spring-loaded check valves. A revolutionary, internalReduced Pressure Zone, located between the check valves, ensures protection and reliable performance of the relief valve.