A pneumatic, or air, tool is driven by various types of air motors or pistons; the power is provided by compressed air from a compressor system.
The air motor has many advantages for use in tools, especially hand-operated ones. The motor is small and light for the high torque and power it delivers, and it does not overheat – even when stalled for long periods – since the flow of air has a cooling effect. It cannot be damaged by overloading. In addition, means can be provided to give instant reversal without causing any damage to the mechanism. Another advantage is that the motor starts almost instantaneously and there is no overrun when the air supply is cut, except in high-speed motors where no gearing is used. The fact that the driving air passes into the tool from a clean supply and is exhausted to the atmosphere means that abrasive or clogging dust can be excluded from the mechanism, making it suitable for use in severe conditions.
Most of these points add up to low maintenance costs, reliability, ease of use and saving in unnecessary fatigue to the operator. Many pneumatic tools are basically similar to power tools driven by electric motors, the main difference being the use of air motors instead of electric ones.
For operation, air tools need a supply of compressed air. The normal working pressure is in the range 80-100 psi (5.5-7 bar), though lower pressures can also be used. Normally the air is supplied by a fixed or portable compressor system. In factories fixed systems are generally used and the compressed air is distributed around the factory by air lines. Outlets are provided for connecting the pneumatic tools; flexible hoses allow free movement of the tools in use. Automatic connectors that cut off the air flow when disconnected are often used, or alternatively a hand-operated valve is fitted to the outlet.