What does a rising gauge needle indicate when test cock #2 is closed during test #5 on the RP?

In the context of testing a Reduced Pressure Principle (RP) backflow preventer, a rising gauge needle while test cock #2 is closed during test #5 indicates that there is an issue with the outlet side of the backflow preventer. Specifically, it most commonly implies that there is a leakage in the outlet shut-off valve.

When test cock #2 is closed, the relief valve should ideally not show an increase in pressure if it's functioning correctly and there is no backflow or leakage occurring. If the gauge needle rises, this suggests that pressure is building up in the relief valve chamber due to backflow. The likely cause of this pressure increase is that the outlet shut-off valve is leaking, which allows some pressure from the downstream side to flow back toward the relief valve, causing the gauge reading to go up.

This scenario highlights the importance of the outlet shut-off valve in maintaining system integrity and preventing backflow into the potable water supply. It demonstrates the functionality and roles of different components within the RP assembly, showing how issues can be diagnosed through gauge readings during testing.