Which type of valve is designed to be either in an open or closed position to prevent backflow?

• A. Check valves
• B. Globe valves
• C. Ball valves
• D. Butterfly valves

Answer: (A)

Backflow prevention is accomplished with a one-way valve. A check valve is designed to let fluid flow in one direction and automatically block it if the flow reverses. It uses a movable element—such as a disc, ball, or poppet—that is pushed open by forward pressure and seals against a seat when reverse pressure appears, so the valve sits open for forward flow and closes to stop backflow without any manual action. Globe valves focus on regulating flow and require operation to open or close, not automatic backflow protection. Ball and butterfly valves provide quick on/off isolation, but they aren’t primarily intended to automatically prevent reverse flow.