In a Reduced Pressure Zone Backflow Preventer, when the supply pressure exceeds the downstream pressure, the relief valve's spring tension keeps the valve closed. Which option corresponds?

• A. The Relief Valve's Spring Tension
• B. Downstream Pressure
• C. Main Valve
• D. Upstream Pressure

Answer: (A)

In an RPZ backflow preventer, the relief valve is spring-loaded to stay closed under normal conditions. When the supply (upstream) pressure is higher than the downstream pressure, the spring tension holds the relief valve shut, preventing venting. The valve only opens when the differential pressure across it exceeds the spring setting, such as during a backflow or backpressure condition. So the element that keeps the valve closed in this scenario is the relief valve’s spring tension. Upstream and downstream pressures determine the force balance but do not themselves keep the valve closed; they simply define the differential that could trigger opening. The main valve controls regular flow but is not the mechanism that keeps the relief valve closed.