In plumbing, what term is used to describe a device that allows flow in one direction only?

The term that describes a device allowing flow in only one direction is a check valve. This component is specifically designed to prevent backflow, ensuring that fluids travel through the plumbing system in the intended direction without the possibility of reversing.

Check valves are critical in various applications, such as preventing contamination in water supply systems by blocking reverse flow. They typically work by utilizing a mechanism, like a spring or a disk, that opens to allow forward flow and closes automatically when the flow tries to reverse, maintaining system integrity and efficiency.

The other types of valves listed serve different purposes. Shut-off valves are designed to stop flow entirely when needed, while ball and gate valves are primarily used for controlling flow rather than restricting it to a single direction. Thus, their functions do not align with the specific purpose of directing flow, making check valves the correct term in this context.