Doug Queen, age 13, of Marquette, Mich., for his question:
WHEN WAS COMPRESSED AIR FIRST USED?
Compressed air is air under pressure greater than that of the atmosphere. Compressed air provides the power for many pneumatic, or air powered, tools, such as drills and hammers, riveting guns and rock drills. The earliest pneumatic transmission dates from 1700, when the French doctor Denis Papin used power from a waterwheel to compress air that was transmitted through tubes.
About 100 years after Dr. Papin, a British inventor named George Medhurst received a patent to use compressed air to drive a motor, although the first practical application is usually credited to the British inventor George Law, who in 1865 devised the rock drill, in which an air drive piston operated a hammer tool.
The rock drill was widely adopted and used in drilling of the Mont Cenis railroad tunnel in the Swiss Alps, opened in 1871, and for the Hoosac tunnel in western Massachusetts, opened in 1875.
Another significant advance was the invention of the pneumatic railroad air brake by the American inventor, engineer and industrialist George Westinghouse about 1868.
When expanded to a lower pressure, compressed air can be used to push a piston, as in a jackhammer; it can go through a small air turbine to turn a shaft as in a dental high speed drill; or it can be expanded through a nozzle to produce a high speed jet as in a paint sprayer.
Compressed air motors are widely used in tools where intermittent large forces are required, as in jackhammers; in hand held tools where an electric motor would be too large to provide the desired torque, as in the pneumatic wrenches used in garages to tighten or loosen lug nuts on automobile wheels; and in small high speed rotary systems where speed in the 10,000 to 30,000 rpm range can easily be achieved.
Pneumatic power is also used extensively in manufacturing plants. An oscillating or rotating motion can be achieved by a crank or ratchet mechanism, although for high speed rotary motion a vane type motor is more suitable. This acts like an air turbine, turning the rotor while the air expands, and is used for high speed drills and grinders and for air sirens.
A compressed air system can also be used to carry other material and spray them through an atomizing nozzle. Paint, for example, can be sucked up into a reduced area section where the air speed is increased while the pressure is being reduced, mixed into the air, dynamically recompressed and discharged through the nozzle.
Sandblasting machines, which pick up sand, operate in a similar manner. The spray type aerosol dispenser also acts as a pneumatic sprayer.