Which device is most effective for preventing backflow when an air gap is not available?

• A. Air Gap
• B. Check Valve
• C. RP (Reduced Pressure)
• D. Atmospheric Vacuum Breaker

Answer: (C)

Backflow prevention aims to keep contaminated water from entering the clean supply. When an air gap isn’t available, the device that provides the strongest protection against both backpressure and back-siphonage is the reduced-pressure principle backflow preventer. It has two check valves with a relief valve between them, creating a maintained reduced-pressure zone. If pressure on the supply side drops or backpressure occurs, the relief valve vents to the atmosphere, preventing reverse flow. This makes it more robust than a simple check valve, which can fail during back-siphonage or pressure fluctuations, and more reliable than an atmospheric vacuum breaker, which offers limited protection and has installation constraints. Air gaps are ideal, but if you can’t use one, the reduced-pressure device gives the best protection.