How Air Cylinders Work

Air cylinders, or pneumatic cylinders, as they are more commonly referred to, serve a variety of purposes. They are flexible devices, and the purpose for which they are being used determines how they work. In their most mundane form, pneumatic cylinders are used to ensure that a storm door or trunk lid closes gently. More exciting uses of the technology include lifting heavy loads or even providing mechanical "muscles" for robots.

Basic Construction

All pneumatic pumps consist of a piston inside of a cylinder. Imagine you have a sealed cylinder containing a piston connected to a shaft that runs the length of the cylinder. If you push the shaft all of the way into the cylinder, the piston is positioned near one end of the cylinder. Now, if you were to force air into that end of the cylinder, the piston would be pushed toward the other end. As the piston is pushed, the shaft is extended away from the cylinder. A load attached to the shaft would be pushed away from the cylinder. If the air cylinder is placed vertically, this simple configuration can be used as a lifting device. As the pressure of the compressed air in the cylinder is decreased, gravity will bring the load back down. This is known as a single action air cylinder, because the compressed air only works in one direction.

Basic Load Return

The basic design described above is fine for some purposes, but the load will only return to the original position with the help of gravity. If the cylinder is upside down, or horizontal, the load will not return to its original position when the air pressure is removed. The most simple solution to this problem is to use a return spring. The compressed air pushes the piston and the shaft against a spring. When the air pressure is removed from the cylinder, the spring pushes the cylinder back to its starting position. This type of load return is limited because the air pressure must be capable of pushing the spring back as well as the piston. This means that the return strength can never match the extension strength.

Advanced Load Return

The use of a spring can be effective for some uses, but others require more force or precision than the spring can provide. The solution to these problems is the use of what is called a double acting pneumatic cylinder. In this setup, compressed air is used at both ends of the cylinder. This is accomplished by having an air inlet port at each end of the cylinder. Valves control the flow of air into the ports. These types of air cylinders are more complex because the when one valve is providing the air pressure, the other must be opened to allow the air out. This is accomplished through the use of an electronic valve called a solenoid. For advanced needs, such as robotics, the valves can be controlled by a computer.

References

• international fluid power society