Which valve prevents backflow in a piping system?

• A. Gate valves
• B. Check valves
• C. Relief valves
• D. Ball valves

Answer: (B)

Backflow prevention relies on a valve that only lets fluid move in one direction. A check valve does exactly that: it opens to allow forward flow and automatically closes if flow reverses, blocking any return or reverse flow. This automatic seal protects pumps, piping, and downstream equipment from damage or contamination, even when pressure changes or the pump stops.

Gate valves and ball valves are primarily on/off isolation devices; they control flow by opening or closing manually or with a actuator, but they don’t automatically prevent reverse flow. Relief valves protect equipment by venting excess pressure, not by blocking reverse flow in a line. So the automatic one-way action of a check valve makes it the best choice for preventing backflow.