A double-acting cylinder will extend when oil flows into the ______.

• A. Cap end
• B. Rod end
• C. Piston
• D. Tank

Answer: (A)

The key idea is how pressure on each end of the piston controls movement. In a double-acting cylinder, there are two hydraulic ports—one at the cap end and one at the rod end. When oil is directed into the cap end, it pushes the piston toward the rod end, causing the piston rod to extend. That outward movement is what we call extension. If oil were sent into the rod end, the piston would move the other way and retract. The tank isn’t an active port; it’s just the reservoir for the fluid. The extension action comes from applying pressure on the cap end, which moves the piston outward.