Which component prevents backflow in a piping system?

• A. Isolation valve
• B. Pressure regulator
• C. Check valve
• D. Relief valve

Answer: (C)

Backflow prevention means stopping fluid from flowing backward in the line. The device that does this automatically is a check valve. It has a movable element (like a disc, ball, or poppet) that is pushed open by forward flow. When flow tries to reverse, the element is pressed against its seat and seals the passage, preventing any reverse movement. This one-way behavior happens without human intervention, making it ideal for stopping backflow in a piping system.

Isolation valves simply block flow in a segment of the line, but they don’t automatically prevent backflow through other paths or when pressure changes elsewhere in the system. A pressure regulator controls downstream pressure but doesn’t stop reverse flow if conditions reverse. A relief valve vents excess pressure to protect equipment, not to prevent backflow.