Short answers, pulled from the story.
A pneumatic cylinder is a mechanical device that uses compressed gas to produce force in a reciprocating linear motion. Compressed air enters the tube at one end of a piston, imparts force on that piston, and the piston rod transfers the resulting force to the object being moved.
Engineers prefer pneumatic cylinders because they are quieter, cleaner, and do not require large amounts of space for fluid storage. Because the operating fluid is air, leaks from a pneumatic cylinder disperse rather than drip, making pneumatics preferable in environments where cleanliness is required.
Pneumatic cylinders are used in the mechanical puppets of the Disney Tiki Room, where compressed air prevents fluid from dripping onto visitors below. Steam-powered rodless mechanical cylinders of a similar design are also used in the catapults aboard modern aircraft carriers.
A single-acting cylinder has one port; compressed air extends the rod in one direction and the rod returns through the same port. A double-acting cylinder has two ports and uses air pressure to drive the rod in both the extending and retracting directions.
Pneumatic cylinders range from 2.5 millimetres in diameter, small enough to handle transistors and electronic components, up to 400 millimetres and beyond. Some cylinders reach 1000 millimetres in diameter and are used in place of hydraulic cylinders in situations where leaking hydraulic oil would pose an extreme hazard.
On the instroke, the piston rod occupies part of the piston face, reducing the effective cross-sectional area that compressed air can act upon. Because force equals pressure multiplied by effective area, a smaller area at the same supply pressure produces less force on the instroke than on the outstroke.