What is a pneumatic cylinder?
A pneumatic cylinder is essentially an industrial air ram. A sealed piston and rod contained within a tube, a pneumatic cylinder uses compressed gas to move the rod back and forth. There are two main types, single acting cylinders and double acting cylinders.

What is a double-acting cylinder?
A double acting cylinder can be moved in both directions (that is, the rod can both extend and retract depending on which side of the piston pressure is applied). A double acting cylinder internally looks like:

As you can see, a double-acting cylinder has two air ports. Depending which port is used, the piston will be pushed to one side or the other, therefore extending/retracting the cylinder. To run a double acting cylinder, you need a 4-way valve. If the cylinder is to move in one direction, the air behind the piston must be exhausted or else it will act as a buffer.

What is a single-acting cylinder?
A single acting cylinder has only 1 port, and can therefore only be controlled in 1 direction. That is, you can have single acting cylinders that have the rod normally retracted and when pressure is applied it will extend and vice versa. Most have an internal return spring, so the rod will return to its original position when there is no pressure applied. A single acting cylinder typically looks like:

To run a single-acting cylinder you need a 3-way valve.

Where can I buy one?
eBay has some good deals most of the time, and Surplus Center is always good. Shipping is decent at Surplus Center, and their usually great selection of cylinders and valves makes it an indispensable source for cheap parts.

So what can you do with these things?
I use them for bolt action uses like on the CylBolt and ChewyCyl. I've got some cannons in the works that will use them for barrel elevation like on modern artillery. I'm eager to see other people begin using cylinders.

Email me if you have any questions: John@NeoSpud.com

all images, text, and other content copyright 2006 John Shell, John@NeoSpud.com