How does a pressure-reducing valve function in relation to flowing conditions?

A pressure-reducing valve (PRV) is designed to control and maintain a specific pressure level within a piping system, regardless of whether the system is under static (no flow) or flowing conditions. When water is flowing through a system, the PRV adjusts to ensure that the downstream pressure remains at a predetermined level, accommodating variations in flow rates and pressures from other system components.

This functionality is crucial in fire protection systems, such as standpipes, as it helps prevent over-pressurization, which could damage the system or cause inefficient operation. Therefore, the correct choice highlights that the valve effectively reduces pressure during both flowing and static conditions, ensuring consistent performance and safety in the system.

In contrast, the other options do not reflect the operational capabilities of a PRV. For instance, a PRV does not operate solely under static conditions, nor does it completely shut off water flow. It also does not merely regulate flow without affecting pressure, as its primary purpose is to manage the pressure within the system while allowing for the necessary flow during an emergency situation.