There's only two main kinds of air cylinders: Double acting, and single acting. They come in all variations, shapes and sizes. Both kinds are useful for haunt work. Double acting cylinders are useful when you need to push in both directions, and single acting cylinders are useful when only a push in one direction is needed. And, sometimes 'in a pinch', you can adapt a double to act as a single, and a single to act as a double.

Air cylinders are measured by three main values: "pressure rating", the "bore", and "stroke"

There are lots of calculations to accurately figure the power of a cylinder, but most haunt pop-up applications can be handled by air cylinders in the range of 3/4" to 1-1/2" bore, and 3" to 8" stroke.

Power measurements primarily take into account the air pressure (the higher the pressure, the more power); and the bore (the larger the bore - the more power). The power ratings are usually only quoted at maximum pressure. So if a cylinder produces180 pounds of 'push', it will only deliver that at the maximum pressure (usually 250 psi for commerical cylinders).

Haunters should work their props at much, much lower pressures than the max pressure. A good goal is not to exceed 60-70psi for working props. Going much higher causes more stress on the prop and all parts in the air system, and makes your compressor run more often. Even at lower pressures, air cylinders can still move very fast and deliver quite a lot push, so always be very careful around pneumatics!

Double Acting means the air pushes the rod out, and pushes the rod in. Without air pushing one way or the other, nothing happens!

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