The function of a check valve is to?

• A. Prevent the reversal of flow in a piping system
• B. Increase flow rate
• C. Filter contaminants
• D. Regulate pressure

Answer: (A)

A check valve is designed to allow flow in one direction and automatically seal to prevent backward flow in a piping or pneumatic system. The internal element—such as a disk, ball, or flap—is pushed open by forward pressure, but if flow reverses, it seats against the valve seat and blocks the reverse flow. This directly prevents reversal of flow, which is why it’s the best description of the valve’s function. The other options point to roles of different components: increasing flow rate is the job of a pump or a less restrictive path, filtering contaminants is what a filter does, and regulating pressure is the role of a regulator.