A check valve only allows flow in which direction?

• A. in two directions
• B. in any direction
• C. reverse only
• D. in one direction

Answer: (D)

A check valve is designed to allow fluid to pass in only one direction and to prevent backflow. When forward pressure pushes the valve open, flow occurs. If the pressure reverses and tries to push flow backward, the closure seats and stops it. Different designs (disc, ball, spring-assisted) all achieve this one-way behavior. That’s why the description of flow occurring in one direction best fits what a check valve does. It doesn’t permit bidirectional flow, reverse-only flow, or flow in any direction without restriction.