What is the function of a check valve in a hydraulic or pneumatic system?

• A. It stores hydraulic energy.
• B. It filters contaminants.
• C. It allows flow in one direction while preventing reverse flow.
• D. It regulates pressure in both directions.

Answer: (C)

A check valve provides unidirectional flow control in hydraulic and pneumatic systems. It acts like a one-way gate: when upstream pressure pushes enough to overcome the valve seat, it opens and fluid or air can pass. If flow tries to go backward or downstream pressure rises, the valve closes and blocks reverse flow. This prevents backflow that could cause unwanted movement or damage and helps keep a circuit charged when the pump is off or a cylinder must hold its position. It doesn’t store energy—that’s an accumulator—nor filter contaminants—that’s a filter—or regulate pressure in both directions—that’s a regulator or relief valve. So the function is to allow flow in one direction while preventing reverse flow.