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Compressed air is air kept under a
pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and ev ...
that is greater than
atmospheric pressure Atmospheric pressure, also known as barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The standard atmosphere (symbol: atm) is a unit of pressure defined as , which is equivalent to 760mm Hg, 29.9212inchesH ...
. Compressed air is an important medium for transfer of energy in industrial processes, and is used for
power tool A power tool is a tool that is actuated by an additional power source and mechanism other than the solely manual labor used with hand tools. The most common types of power tools use electric motors. Internal combustion engines and compressed air ar ...
s such as
air hammer
air hammer
s,
drills A drill or drilling machine is a tool primarily used for making round holes or driving fasteners. It is fitted with a bit, either a drill or driver, depending on application, secured by a chuck. Some powered drills also include a hammer funct ...

drills
,
wrench A wrench or spanner is a tool used to provide grip and mechanical advantage in applying torque to turn objects—usually rotary fasteners, such as nuts and bolts—or keep them from turning. In the UK, Ireland, Australia, and New Zealand ''s ...

wrench
es and others, as well as to atomize paint, to operate air cylinders for automation, and can also be used to propel vehicles. Brakes applied by compressed air made large railway trains safer and more efficient to operate. Compressed air brakes are also found on large highway vehicles. Compressed air is used as a breathing gas by
underwater divers Underwater divers are people who take part in underwater diving activities – Underwater diving is practiced as part of an occupation, or for recreation, where the practitioner submerges below the surface of the water or other liquid for ...

underwater divers
. It may be carried by the diver in a high pressure
diving cylinder A diving cylinder or diving gas cylinder is a gas cylinder used to store and transport high pressure gas used in diving operations. This may be breathing gas used with a scuba set, in which case the cylinder may also be referred to as a scuba ...

diving cylinder
, or
supplied from the surface
supplied from the surface
at lower pressure through an
air line An air line is a tube, or hose, that contains and carries a compressed air supply. In industrial usage, this may be used to inflate car or bicycle tyres or power tools worked by compressed air, for breathing apparatus in hazardous environments and ...

air line
or
diver's umbilical Surface-supplied diving is diving using equipment supplied with breathing gas using a diver's umbilical from the surface, either from the shore or from a diving support vessel, sometimes indirectly via a diving bell. This is different from scuba ...

diver's umbilical
. Similar arrangements are used in breathing apparatus used by firefighters, mine rescue workers and industrial workers in hazardous atmospheres. In Europe, 10 percent of all industrial electricity consumption is to produce compressed air—amounting to 80
terawatt hour The kilowatt-hour (SI symbol: kW⋅h or kW h; commonly written as kWh) is a unit of energy equal to 3600 kilojoules (3.6 megajoules). The kilowatt-hour is commonly used as a billing unit for energy delivered to consumers by electri ...

terawatt hour
s consumption per year.


History

Industrial use of piped compressed air for power transmission was developed in the mid 19th century; unlike
steam Steam is water in the gas phase. This may occur due to evaporation, to due to boiling, where heat is applied until water reaches the enthalpy of vaporization. Steam that is saturated or superheated is invisible; however, "steam" often refers to ...

steam
, compressed air could be piped for long distances without losing pressure due to condensation. An early major application of compressed air was in the drilling of the
Mont Cenis Tunnel Mont may refer to: Places * Mont., an abbreviation for Montana, a U.S. state * Mont, Belgium (disambiguation), several places in Belgium * Mont, Hautes-Pyrénées, a commune in France * Mont, Pyrénées-Atlantiques, a commune in France * Mont, Saô ...

Mont Cenis Tunnel
in Italy and France in 1861, where a 600 kPa (87 psi) compressed air plant provided power to
pneumatic drills
pneumatic drills
, increasing productivity greatly over previous manual drilling methods. Compressed air drills were applied at mines in the United States in the 1870s.
George Westinghouse George Westinghouse Jr. (October 6, 1846 – March 12, 1914) was an American entrepreneur and engineer based in Pennsylvania who created the railway air brake and was a pioneer of the electrical industry, receiving his first patent at the age of 1 ...

George Westinghouse
invented
air brakes
air brakes
for trains starting in 1869; these brakes considerably improved the safety of rail operations. In the 19th century, Paris had a system of pipes installed for municipal distribution of compressed air to power machines and to operate generators for lighting. Early air compressors were steam-driven, but in certain locations a
trompe 180px|A Catalan forge trompe A trompe is a water-powered air compressor, commonly used before the advent of the electric-powered compressor. A trompe is somewhat like an airlift pump working in reverse. Trompes were used to provide compressed ai ...

trompe
could directly obtain compressed air from the force of falling water.


Breathing

Air for breathing may be stored at high pressure and gradually released when needed, as in
scuba diving#REDIRECT Scuba diving#REDIRECT Scuba diving {{R from other capitalisation ...
{{R from other capitalisation ...

scuba diving
, or produced continuously to meet requirements, as in
surface-supplied diving Surface-supplied diving is diving using equipment supplied with breathing gas using a diver's umbilical from the surface, either from the shore or from a diving support vessel, sometimes indirectly via a diving bell. This is different from scuba ...

surface-supplied diving
. Air for breathing must be free of oil and other contaminants; carbon monoxide, for example, in trace volumetric fractions that might not be dangerous at normal atmospheric pressure may have deadly effects when breathing pressurized air due to proportionally higher
partial pressure In a mixture of gases, each constituent gas has a partial pressure which is the notional pressure of that constituent gas if it alone occupied the entire volume of the original mixture at the same temperature. The total pressure of an ideal gas mixt ...

partial pressure
. Air compressors, filters, and supply systems intended for breathing air are not generally also used for pneumatic tools or other purposes, as air quality requirements differ. Workers constructing the foundations of bridges or other structures may be working in a pressurized enclosure called a
caisson
caisson
, where water is prevented from entering the open bottom of the enclosure by filling it with air under pressure. It was known as early as the 17th century that workers in
diving bell A diving bell is a rigid chamber used to transport divers from the surface to depth and back in open water, usually for the purpose of performing underwater work. The most common types are the open-bottomed wet bell and the closed bell, which ca ...

diving bell
s experienced shortness of breath and risked asphyxia, relieved by the release of fresh air into the bell. Such workers also experienced pain and other symptoms when returning to the surface, as the pressure was relieved.
Denis Papin Denis Papin FRS (; 22 August 1647 – 26 August 1713) was a French physicist, mathematician and inventor, best known for his pioneering invention of the steam digester, the forerunner of the pressure cooker and of the steam engine. Early life a ...

Denis Papin
suggested in 1691 that the working time in a diving bell could be extended if fresh air from the surface was continually forced under pressure into the bell. By the 19th century, caissons were regularly used in civil construction, but workers experienced serious, sometimes fatal, symptoms on returning to the surface, a syndrome called
caisson disease
caisson disease
or
decompression sickness Decompression sickness (DCS; also known as divers' disease, the bends, aerobullosis, or caisson disease) describes a condition arising from dissolved gases coming out of solution into bubbles inside the body on depressurisation. DCS most common ...

decompression sickness
. Many workers were killed by the disease on projects such as the
Brooklyn Bridge The Brooklyn Bridge is a hybrid cable-stayed/suspension bridge in New York City, spanning the East River between Manhattan Island and Brooklyn on Long Island. Opened on May 24, 1883, the Brooklyn Bridge was the first fixed crossing of the East R ...

Brooklyn Bridge
and the
Eads Bridge Eads Bridge is a combined road and railway bridge over the Mississippi River connecting the cities of St. Louis, Missouri and East St. Louis, Illinois. It is located on the St. Louis riverfront between Laclede's Landing, to the north, and the gr ...

Eads Bridge
and it was not until the 1890s that it was understood that workers had to decompress slowly, to prevent the formation of dangerous bubbles in tissues. Air under moderately high pressure, such as is used when diving below about , has an increasing
narcotic Heroin, a powerful opioid and narcotic The term narcotic (, from ancient Greek ναρκῶ ''narkō'', "to make numb") originally referred medically to any psychoactive compound with numbing or paralysing properties. In the United States, it has ...

narcotic
effect on the nervous system.
Nitrogen narcosis Narcosis while diving (also known as nitrogen narcosis, inert gas narcosis, raptures of the deep, Martini effect) is a reversible alteration in consciousness that occurs while diving at depth. It is caused by the anesthetic effect of certain gase ...

Nitrogen narcosis
is a hazard when diving. For diving much beyond , it is less safe to use air alone and
special breathing mixes
special breathing mixes
containing helium are often used.


Uses of compressed air

In industry, compressed air is so widely used that it is often regarded as the fourth utility, after electricity, natural gas and water. However, compressed air is more expensive than the other three utilities when evaluated on a per unit energy delivered basis. Compressed air is used for many purposes, including: *
Pneumatics Pneumatics (from Greek ‘wind, breath’) is a branch of engineering that makes use of gas or pressurized air. Pneumatic systems used in industry are commonly powered by compressed air or compressed inert gases. A centrally located and electri ...

Pneumatics
, the use of pressurized gases to do work **
Pneumatic post
Pneumatic post
, using capsules to move paper and small goods through tubes. **
Air toolDrilling a blast hole with a pneumatic drill (jackhammer). A pneumatic tool, air tool, air-powered tool or pneumatic-powered tool is a type of power tool, driven by compressed air supplied by an air compressor. Pneumatic tools can also be driven by c ...

Air tool
s **
HVAC control system HVAC (Heating, Ventilation and Air Conditioning) equipment needs a control system to regulate the operation of a heating and/or air conditioning system. Usually a sensing device is used to compare the actual state (e.g. temperature) with a target st ...

HVAC control system
s **
spray painting Spray painting is a painting technique in which a device sprays coating material (paint, ink, varnish, etc.) through the air onto a surface. The most common types employ compressed gas—usually air—to atomize and direct the paint particles. Spra ...

spray painting
* Vehicle propulsion (''see''
compressed air vehicle A compressed-air vehicle (CAV) is a transport mechanism fueled by tanks of pressurized atmospheric gas and propelled by the release and expansion of the gas within a Pneumatic motor. CAV's have found application in torpedoes, locomotives used in ...

compressed air vehicle
) *
Energy storage Energy storage is the capture of energy produced at one time for use at a later time to reduce imbalances between energy demand and energy production. A device that stores energy is generally called an accumulator or battery. Energy comes in mul ...

Energy storage
(''see''
compressed air energy storage Compressed-air energy storage (CAES) is a way to store energy generated at one time for use at another time using compressed air. At a utility scale, energy generated during periods of low energy demand (off-peak) can be released to meet higher de ...

compressed air energy storage
) * Air brakes, including: **
railway braking systems
railway braking systems
**
road vehicle braking systems
road vehicle braking systems
*
Underwater diving#REDIRECT Underwater diving#REDIRECT Underwater diving {{R for alternate capitalisation ...
{{R for alternate capitalisation ...

Underwater diving,
for breathing
for breathing
, to inflate
buoyancy compensator devices
buoyancy compensator devices
and
lifting bag A lifting bag is an item of diving equipment consisting of a robust and air-tight bag with straps, which is used to lift heavy objects underwater by means of the bag's buoyancy. The heavy object can either be moved horizontally underwater by the d ...

lifting bag
s, and for
airlift dredging
airlift dredging
*
Refrigeration The term refrigeration means cooling a space, substance or system to lower and/or maintain its temperature below the ambient one (while the removed heat is rejected at a higher temperature).International Dictionary of Refrigeration, http://diction ...

Refrigeration
using a
vortex tube , revealed by colored smoke In fluid dynamics, a vortex (plural vortices/vortexes) is a region in a fluid in which the flow revolves around an axis line, which may be straight or curved. Vortices form in stirred fluids, and may be observed in smo ...

vortex tube
*
Air-start system 250px|Cutaway of an air-start system of a General Electric J79 [[turbojet. The small turbine (next to yellow shaft) and [[epicyclic gearing (to right of perforated metal screen) are clearly visible. An air-start system is a power source used to prov ...

Air-start system
s in engines * Ammunition propulsion in: ** [[Air guns ** [[Airsoft equipment ** [[Paintball equipment * Cleaning dust and small debris in tiny spaces * [[Abrasive blasting for removing corrosion products and coatings * [[Injection molding * [
irbrush
irbrush
ing used by
model railroaders
model railroaders
and other hobbyists to paint and weather cars, boats, planes and trains * Food and beverage capping and
fermentation Fermentation is a metabolic process that produces chemical changes in organic substrates through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in the absence of oxygen. In food prod ...

fermentation
* Compressed air from Lysefjorden/[[Preikestolen (Norway) is being sold in cans, mostly to China.


Design of systems

Compressor rooms must be designed with ventilation systems to remove [[waste heat produced by the compressors.


Water and oil vapor removal

When air at atmospheric pressure is compressed, it contains much more water vapor than the high-pressure air can hold. [[Relative humidity is governed by the properties of water and is not affected by air pressure. After compressed air cools, then the vaporized water turns to liquefied water. Cooling the air as it leaves the compressor will take most of the moisture out before it gets into the piping. Aftercooler, storage tanks, etc. can help the compressed air cool to 104 °F; two-thirds of the water then turns to liquid. Management of the excessive moisture is a requirement of a compressed air distribution system. System designers must ensure that piping maintains a slope, to prevent accumulation of moisture in low parts of the piping system. Drain valves may be installed at multiple points of a large system to allow trapped water to be blown out. Taps from piping headers may be arranged at the tops of pipes, so that moisture is not carried over into piping branches feeding equipment. Piping sizes are selected to avoid excessive energy loss in the piping system due to excess velocity in straight pipes at times of peak demand, or due to turbulence at pipe fittings.


See also

* * * * * – (generally use fluorocarbons but some use compressed air.) *


Notes


External links

* {{DEFAULTSORT:Compressed Air [[Category:Compressed air power|. [[Category:Breathing gases [[Category:Gas technologies [[Category:Energy storage [[Category:Industrial gases [[Category:Pneumatics [[Category:Respiration