Which valve traps the fluid under pressure until pilot pressure overcomes the spring force and is sometimes called running away?

• A. Counterbalance valve
• B. Throttle type restrictor
• C. One-way control valve
• D. Flow control valve

Answer: (A)

When a hydraulic actuator has a load on it, gravity can cause motion if the fluid is free to move back. A counterbalance valve is designed to prevent that by holding the actuator in place. It is spring-biased and pilot-operated, so fluid on the cylinder side becomes trapped under pressure behind the valve. This held pressure resists the load. Only when a pilot pressure is applied that is strong enough to overcome the spring does the valve open enough to allow fluid to move and the motion to continue. That trapping and the need for pilot pressure to overcome the spring is why this valve is associated with the term running away—and why it’s used to prevent it.

This is the best choice because it directly provides the holding function you need to counteract a load and requires a pilot signal to release, ensuring controlled motion. The other valves don’t perform this role: a throttle-type restrictor mainly controls speed by restricting flow but doesn’t lock in a held position; a one-way control valve (check valve) allows flow in only one direction and doesn’t maintain a held pressure to resist load; a flow control valve regulates rate but not the necessary hold to prevent load runaway.