Name two common backflow prevention devices used in irrigation systems and a key difference between them.

• A. Check valve and air gap; both protect equally against backflow.
• B. Double-check valve and reduced pressure principle backflow preventer; DC protects primarily against back-siphonage, RPZ protects against both backflow and back-siphonage and includes test ports.
• C. Ball valve and RPZ; RPZ only provides pressure relief.
• D. Isolation valve and DC; DC eliminates all backflow risk.

Answer: (B)

This question tests understanding of two common irrigation backflow preventers and how their protection differs. A double-check valve uses two check valves in series to block backflow and is mainly aimed at preventing back-siphonage; it provides basic protection and is simpler and cheaper, with fewer maintenance requirements. A reduced pressure principle backflow preventer adds a relief valve between two check valves and includes test ports; it protects against both backflow and back-siphonage and is designed for higher-hazard situations, with ongoing inspection and certification.

So the best choice pairs these two devices and notes the key difference: the DC offers limited protection focused on back-siphonage, while the RPZ provides broader protection (against backflow and back-siphonage) and has test ports for maintenance.