What is the purpose of a check valve in standpipe systems?

The purpose of a check valve in standpipe systems is to prevent backflow of water. This is crucial for maintaining the integrity and functionality of the fire protection system. When water flows through a standpipe, it is essential that it does not flow back in the reverse direction, as this could contaminate the water supply and reduce the effectiveness of the system in emergency situations. By preventing backflow, the check valve ensures that water can only move in a single direction—toward the areas that require it, such as upper floors of a building during a fire. This protective mechanism is vital for safeguarding both the water supply and the safety of occupants in the building. The other options don't address the primary function of a check valve in this context, which is focused specifically on preventing backflow rather than increasing flow, monitoring quality, or connecting systems.