Why does the Relief Valve (RV) drip after closing the customer's shut-off valve?

The reason the Relief Valve (RV) might drip after the customer's shut-off valve has been closed is primarily due to a leak in the first check valve (CV #1). This situation occurs because the RV is designed to allow any excess pressure or backflow to be discharged to prevent potential contamination or system failure. If CV #1 is not sealing properly, it can allow water to seep back through the system, causing the RV to drip even when the shut-off valve is closed.

When CV #1 is functioning properly, it should completely seal the flow coming from the public water supply. However, if there is a failure in this check valve, the pressure from downstream or any residual pressure can force water past the valve, leading to a situation where the RV activates by releasing that excess water. This continual leakage from CV #1 is a common cause for the dripping observed at the RV.

The other options do not directly address the mechanism of why the RV drips. A malfunctioning RV (the first option) would typically cause more significant issues rather than just dripping. High supply pressure (the third option) is less likely to be the sole cause if the RV is designed to handle those conditions. Lastly, not meeting air gap requirements (the fourth option