What is the function of a check valve?

• A. To increase system pressure
• B. To limit pressure
• C. To allow fluid flow in one direction and prevent reverse flow
• D. To filter contaminants

Answer: (C)

A check valve acts like a one-way gate in a pipe. Its purpose is to let fluid move in the intended direction while stopping any attempt of the fluid to flow backward. This unidirectional flow is essential to prevent backflow that could cause water hammer, siphoning, or damage to pumps and downstream equipment. The valve usually uses a movable element—a disk, ball, or flap—that rests on a seat to block reverse flow. When forward pressure pushes the gate open, fluid passes through; if pressure on the outlet side tries to push the gate back, the gate seals and blocks the flow. It doesn’t increase or limit pressure, nor does it filter contaminants—that’s the role of a pump, regulator, or filter, respectively. In many systems, a check valve is placed after a pump or near equipment to ensure fluids don’t return, preserving system integrity.