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What Is a Pneumatic Cylinder?

A bicycle pump is a form of pneumatic cylinder.
A pneumatic cylinder.
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  • Written By: E.A. Sanker
  • Edited By: John Allen
  • Last Modified Date: 06 August 2014
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A pneumatic cylinder is a type of device used to generate force from the energy of pressurized gas. The basic pneumatic cylinder consists of a cylindrical chamber with a movable piston and intake and exhaust channels. When compressed air or other gas is pumped into the bottom of the cylinder, the gas expands, pushing the movable piston upwards and generating force. Pneumatic cylinders, also known as air cylinders, have advantages over hydraulics in some cases and are used in a wide variety of applications.

In order to operate the cylinder, a gas, such as air, must first be pressurized. This can be done using a pump. Since air usually exists at atmospheric pressure, pumps are used to force a certain volume of air into a smaller space, causing its pressure to increase to above the atmospheric level. The pressurized air stores the energy used in compressing it. When allowed to expand, this air will tend to depressurize back to its original atmospheric pressure.

A pneumatic cylinder operates based on this principle. Air is compressed and then routed into the cylindrical chamber beneath a movable piston. The pressurized air exerts force against the base of the piston, causing the piston to move upward through the hollow cylinder. A rod extends from the base of the piston up through the top of the cylinder. When compressed air expands into the given space and moves the piston upwards, this rod also moves, providing a way to move other mechanical elements.

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The position of the piston in a pneumatic cylinder is controlled by a valve that routes compressed air into either the top or bottom of the cylinder. When the rod end, or top, of the cylinder is filled with pressurized air, the piston moves downwards, and air beneath the piston is vented out through an exhaust pipe. Pressurized air entering the base moves the piston up, and the air above the piston is vented out. This system allows the cylinder to be operated repeatedly to generate force.

Pneumatic systems have several advantages over hydraulics, which use water or another fluid to generate mechanical motion. The exhaust air from a pneumatic cylinder can be released into the surrounding air without environmental concerns. Air is easy to obtain and pressurize. Furthermore, leaks are not a concern with pneumatic systems. The disadvantages of pneumatics include the necessity of operating such systems at high pressure, which can be dangerous, as well as the need to keep the air clean and filtered.

Several familiar mechanical devices use pneumatics. Nail guns, used in construction to drive nails into wood or concrete, draw their force from one or more pneumatic cylinders. Other examples include bicycle pumps and the air brakes used on buses and trucks. In addition to consumer applications, pneumatic cylinders are also widely used in industrial settings, such as packaging plants and machine shops.

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