Pneumatics, in the most general sense, is a branch of science and engineering that concerns itself with pressurized gases. These gases can be anything, including pressurized air. The use of air or other inert gases creates power that can be safer, more reliable, more flexible, or less expensive than electric or internal combustion actuators or motors. One such application would be indoor systems or other closed environments in which exhaust would be unsafe. Also, electricity requires a source, whereas a hydraulic system can be easier to contain.
Gases used in pneumatics are pretty much always inert, for safety reasons. However, different gases have different properties. Certain gases are less expensive than others. Some are heavier than others.
In fixed installations, such as a factory, the pneumatic systems usually use compressed air. This is the most efficient and affordable system since a supply is readily available by compressing atmospheric air. Typically, the air is dehumidified so that it does not rust or corrode the machinery with moisture. Then, a tiny amount of oil is added to the machine to lubricate the machine equipment and protect from corrosion. This is also a very safe system since one need not worry about leaks since the gas is just air. The only concern would be the actual pressure of the escaping air.
One of the disadvantages of atmospheric air is the moisture content as well as pollution. Because atmospheric air has moisture, it must be scrubbed dry before it can be used. Also, it must be filtered to remove pollution, dust, and dirt suspended in the air. The amount of work needed to clean the air depends on the atmosphere, obviously. Machine equipment in Bloomington, Indiana would not need to work as hard dehumidifying the air as the same machine in Miami.
Smaller systems that do not have the capability to process atmospheric air might use other gases. Typically, these would also be used for portable systems. Many of these types of systems use nitrogen, which presents an asphyxiation hazard. This gas, typically called oxygen-free nitrogen (OFN), is not breathable even though nitrogen comprises 78% of atmospheric air. Though it is an asphyxiation hazard, it is cheaper than oxygen and is non-combustible, making it ideal for use in pneumatic machine equipment.
Other machines, such as portable tools or vehicles, often run on compressed carbon dioxide (CO2). This is typically done because the gas is inert, easily compressed, and readily available. Also, the gas can be compressed into a liquid form which means that more of it can be contained than compressed air. However, carbon dioxide does present an asphyxiation hazard as well as a freezing hazard. Care should be taken when venting the gas.
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