Which valve must be closed when testing a Reduced Pressure Zone (RPZ) assembly?

In testing a Reduced Pressure Zone (RPZ) assembly, it is essential to close the specific shut-off valve to ensure accurate testing results. The correct choice involves closing the Number 2 shut-off valve. This valve is positioned downstream of the RPZ assembly and serves to isolate the assembly from the system during testing. By closing this valve, you prevent water from flowing back through the assembly while you are testing it, which ensures that the pressure differential necessary for the RPZ's operation is maintained. This is critical for accurately assessing whether the RPZ is functioning properly and is effective in preventing backflow.

The other shut-off valves may serve different roles within the operation and configuration of the RPZ. For instance, closing an upstream valve can disrupt service or introduce inaccuracies in measuring the pressure levels across the assembly, while the valve associated with the downstream side might not play a direct role in the testing process. Hence, understanding which valve to manipulate for precise testing of the RPZ is crucial for maintaining system integrity and ensuring compliance with backflow prevention standards.