Describe a double-acting cylinder and how both extend and retract are powered.

• A. Both extend and retract are powered by electricity.
• B. Only extend is powered by air; retract is by gravity.
• C. Both extend and retract are powered by air pressure applied to opposite ends; exhaust ports vent air as it moves.
• D. Air powers extension only; retraction uses a spring.

Answer: (C)

A double-acting cylinder uses compressed air on both sides of the piston to control movement in two directions. Air is applied to one end to push the piston and extend the rod, then air is applied to the opposite end to push it back and retract the rod. The exhaust ports vent the displaced air as the piston moves, preventing pressure from building up on the opposite side and allowing smooth, controlled motion in both directions. There’s no reliance on gravity or a spring for the retraction, and while electricity may power the valve that directs the air, the cylinder’s movement itself is driven by air pressure on both ends.