Describe a single-acting cylinder and a typical return mechanism.

• A. A single-acting cylinder uses air to move in both directions.
• B. A single-acting cylinder relies on a vacuum to move.
• C. A single-acting cylinder uses water pressure to move.
• D. A single-acting cylinder uses air to move in one direction; a spring or external return mechanism resets it when air is vented.

Answer: (D)

A single-acting cylinder provides motion in only one direction with compressed air, and it relies on a return mechanism to reset when the air is vented. The piston is driven by air on one side, while the other side is sealed or blocked. When the supply is released, a spring inside the cylinder or an external force (like gravity or a mechanical return) pushes the piston back to its starting position. This setup contrasts with cylinders that use air pressure on both sides to move in and out, which are double-acting. It also wouldn’t typically use a vacuum or water pressure, since pneumatics uses compressed air for actuation rather than vacuum or hydraulics.