The backflow preventer valve is a critical component for any rainwater harvesting system that is connected by some way to the municipal water supply.

See here critical design elements for a rainwater harvesting system

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

Materials and Corrosion Protection
Made of durable, non-corrosive plastic thermal resin material.
Stainless steel screws and springs.

Application Range
Operating pressure up to 10 Bar .
Maximum operating temperature: 44°C.
For irrigation systems, water handling applications, potable water lines and all other installations requiring protection against backsiphonage and backpressure of contaminated liquids.