What device allows water to flow in only one direction on a fire department connection?

The correct response identifies a clapper valve as the device that enables water to flow in only one direction on a fire department connection. A clapper valve operates by utilizing a hinged flap (the clapper) that opens to allow water to enter the system when pressure is applied from the source. However, if water attempts to flow back in the reverse direction, the clapper automatically closes, preventing backflow. This function is critical for maintaining the integrity of the water supply system and ensuring that contaminated water does not return into the source supply.

While backflow preventers also serve to prevent the reverse flow of water, they generally function differently by creating a one-way barrier that stops backflow based on specific principles or mechanisms, rather than the mechanical flap of a clapper valve. A pressure relief valve's purpose is to regulate excess pressure within a system, which does not relate to unidirectional water flow. Finally, a flow meter is designed to measure the amount of water flowing through a system, but it does not control the direction of flow. Therefore, the clapper valve is specifically suited for ensuring unidirectional flow in fire department connections.