Which statement describes the operation of a reduced pressure principle backflow assembly?

• A. It uses two checks and a relief valve to open and drain when a pressure differential occurs between the two checks
• B. It uses a single check valve
• C. It has no relief valve
• D. The relief valve will open and drain if a pressure differential occurs between the two checks

Answer: (D)

At the heart of a reduced pressure principle backflow assembly is the relief valve that sits between two check valves. The two checks provide isolation to prevent reverse flow, but the key feature is the relief valve opening when pressure between the checks changes. If backflow conditions arise—such as backpressure or back-siphonage—the relief valve will open and discharge to the drain, venting the space between the checks so contaminated water cannot be drawn back into the supply. This draining action is what stops backflow from occurring, making the statement about the relief valve opening and draining under a pressure differential between the checks the accurate description.