____________ pilot-operated check valves is/are used in load-lock circuits when forces act in both directions on a cylinder or forces act to retract a cylinder.

____________ pilot-operated check valves is/are used in load-lock circuits when forces act in both directions on a cylinder or forces act to retract a cylinder.

• A. One
• B. Two
• C. Three
• D. Four

Answer: (B)

Bi-directional load locking is what this question tests. A pilot-operated check valve acts as a controlled one-way lock: in the absence of a pilot signal it blocks flow in its intended direction, and when a pilot pressure is applied it allows flow to pass for that direction. In a load-lock circuit where the cylinder could be pushed or pulled by external forces, you need to prevent movement in both directions when the system isn’t actively commanded. Using two pilot-operated check valves provides a true bi-directional lock. One valve blocks movement in the forward direction (extension) until you energize its pilot to permit it, while the other blocks movement in the opposite direction (retraction) until you energize its pilot to permit that direction. This arrangement ensures the load cannot move no matter which way the forces act, unless you deliberately energize the appropriate pilot to move in the commanded direction. A single valve would only lock one direction, and adding more than two isn’t necessary to achieve the required bi-directional hold.

Bi-directional load locking is what this question tests. A pilot-operated check valve acts as a controlled one-way lock: in the absence of a pilot signal it blocks flow in its intended direction, and when a pilot pressure is applied it allows flow to pass for that direction. In a load-lock circuit where the cylinder could be pushed or pulled by external forces, you need to prevent movement in both directions when the system isn’t actively commanded.

Using two pilot-operated check valves provides a true bi-directional lock. One valve blocks movement in the forward direction (extension) until you energize its pilot to permit it, while the other blocks movement in the opposite direction (retraction) until you energize its pilot to permit that direction. This arrangement ensures the load cannot move no matter which way the forces act, unless you deliberately energize the appropriate pilot to move in the commanded direction. A single valve would only lock one direction, and adding more than two isn’t necessary to achieve the required bi-directional hold.