Which valve allows fluid flow in only one direction and is comprised of a ball, ball seat, and spring?

• A. Jettison Valve
• B. Check Valve
• C. Cross-Feed Valve
• D. Separation/Isolation Valve

Answer: (B)

One-way flow is achieved with a check valve, which uses a moving element that can seal against a seat to block flow when pressure tries to reverse. In a spring-loaded ball check valve, a ball sits on a ball seat. Forward pressure pushes the ball away from the seat, opening the path and allowing fluid to pass. If flow reverses or pressure drops, the spring pushes the ball back onto the seat, sealing the orifice and stopping backflow. The combination of a ball, ball seat, and spring provides reliable, quick sealing against reverse flow, which is exactly what prevents unwanted backflow in a system. Other valve types have different purposes (releasing material, routing flow, or isolating lines), whereas this configuration is specifically for preventing backflow.