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Compressed air is
air An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosph ...
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 eve ...
that is greater than
atmospheric pressure Atmospheric pressure, also known as air pressure or 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 1,013. ...
. Compressed air in vehicle
tire A tire (North American English) or tyre (Commonwealth English) is a ring-shaped component that surrounds a Rim (wheel), wheel's rim to transfer a vehicle's load from the axle through the wheel to the ground and to provide Traction (engineeri ...
s and
shock absorber A shock absorber or damper is a mechanical or hydraulics, hydraulic device designed to absorb and Damping ratio, damp shock (mechanics), shock impulses. It does this by converting the kinetic energy of the shock into another form of energy (typic ...
s are commonly used for improved traction and reduced vibration. Compressed air is an important medium for the transfer of energy in industrial processes and is used for
power tool A power tool is a tool that is actuator, actuated by an additional engine, power source and mechanism (engineering), mechanism other than the solely manual labour, manual labor used with hand tools. The most common types of power tools use electric ...
s such as air hammers, drills, wrenches, 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. The diver may carry it 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 scub ...
, or supplied from the surface at lower pressure through an air line or 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 A kilowatt-hour ( unit symbol: kW⋅h or kW h; commonly written as kWh) is a non-SI unit of energy equal to 3.6 megajoules (MJ) in SI units, which is the energy delivered by one kilowatt of power for one hour. Kilowatt-hours are a commo ...
s consumption per year. Industrial use of piped compressed air for power transmission was developed in the mid-19th century; unlike
steam Steam is water vapor, often mixed with air or an aerosol of liquid water droplets. This may occur due to evaporation or due to boiling, where heat is applied until water reaches the enthalpy of vaporization. Saturated or superheated steam is inv ...
, 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 in Italy and France in 1861, where a 600 kPa (87 psi) compressed air plant provided power to 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 a prolific American inventor, engineer, and entrepreneurial industrialist based in Pittsburgh, Pennsylvania. He is best known for his creation of the railway air brake and for bei ...
invented 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 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 air for bloomery furnaces ...
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 Scuba diving is a Diving mode, mode of underwater diving whereby divers use Scuba set, breathing equipment that is completely independent of a surface breathing gas supply, and therefore has a limited but variable endurance. The word ''scub ...
and self-contained breathing apparatus (SCBA) or used by firefighters and industrial workers, or produced continuously to meet requirements, as in
surface-supplied diving Surface-supplied diving is a mode of underwater diving using equipment supplied with breathing gas through a diver's umbilical from the surface, either from the shore or from a diving support vessel, sometimes indirectly via a diving bell. ...
. 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 as if it alone occupied the entire volume of the original mixture at the same temperature. The total pressure of an ideal g ...
. 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, 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 c ...
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, the steam engine, the centrifug ...
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 or
decompression sickness Decompression sickness (DCS; also called divers' disease, the bends, aerobullosis, and caisson disease) is a medical condition caused by dissolved gases emerging from Solution (chemistry), solution as bubbles inside the body tissues during D ...
. Many workers were killed by the disease on projects such as the Brooklyn Bridge and the
Eads Bridge The 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, St. Louis, Lacled ...
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 The term narcotic (, from ancient Greek ναρκῶ ''narkō'', "I make numb") originally referred medically to any psychoactive compound with numbing or paralyzing properties. In the United States, it has since become associated with opiates ...
effect on the nervous system. Nitrogen narcosis is a hazard when diving. For diving much beyond , it is less safe to use air alone and special breathing mixes containing helium are often used. In land-based applications,
SCBA A self-contained breathing apparatus (SCBA) is a respirator worn to provide an autonomous supply of breathable gas in an atmosphere that is immediately dangerous to life or health from a gas cylinder. They are typically used in firefighting a ...
s, UEBSS (USA), and EBBS (EU) provide breathable air for emergency responders, industrial workers, and military personnel in hazardous environments. These devices use compressed air cylinders to supply clean air to the wearer, ensuring safety in oxygen-deficient or contaminated atmospheres. To enhance operational safety and efficiency, Kee Connections Buddy Breather coupling allows users to share air in emergency situations. This coupling system enables firefighters or other SCBA users to connect their breathing apparatuses, providing life-saving air support when needed. Such innovations help improve survivability and teamwork in high-risk conditions.


Uses

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 the use of gas or pressurized air in mechanical systems. Pneumatic systems used in industry are commonly powered by compressed air or compressed inert gases. A centrally located and electrically- ...
, the use of pressurized gases to do work ** Pneumatic post, using capsules to move paper and small goods through tubes. ** Air tools **
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 s ...
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 compressor, air—to atomize and direct the pa ...
* Vehicle propulsion (''see'' 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 (energy), accumulator or Batte ...
(''see'' compressed-air energy storage) * Recreation – Amusement Parks, Golf Courses (Sprinkler Systems), Hotel elevators, Ski Resorts (Snow making) * Air brakes, including: ** Railway braking systems ** Road vehicle braking systems *
Underwater diving Underwater diving, as a human activity, is the practice of descending below the water's surface to interact with the environment. It is also often referred to as diving (disambiguation), diving, an ambiguous term with several possible meani ...
, for breathing, to inflate buoyancy compensator devices and lifting bags, and for airlift dredging *
Refrigeration Refrigeration is any of various types of cooling of a space, substance, or system to lower and/or maintain its temperature below the ambient one (while the removed heat is ejected to a place of higher temperature).IIR International Dictionary of ...
using a vortex tube * Air-start systems in engines * Ammunition propulsion in: **
Air gun An air gun or airgun is a gun that uses energy from compressed air or other gases that are mechanically pressurized and then released to propel and accelerate projectiles, similar to the principle of the primitive blowgun. This is in contr ...
s **
Airsoft Airsoft, also known as survival game () in Japan where it was popular, is a team sport, team-based shooting sport, shooting game in which participants eliminate opposing players out of play by shooting them with airsoft pellets, spherical plast ...
equipment **
Paintball Paintball is a competitive sport, competitive team sport, team shooting sport in which players eliminate opponents from play by hitting them with spherical dye-filled gelatin capsules called Paintball equipment#Paintballs, paintballs that b ...
equipment * Cleaning dust and small debris in tiny spaces *
Abrasive blasting Sandblasting, sometimes known as abrasive blasting, is the operation of forcibly propelling a stream of abrasive material against a surface under high pressure to smooth a rough surface, roughen a smooth surface, shape a surface or remove sur ...
for removing corrosion products and coatings *
Injection molding Injection moulding (U.S. spelling: injection molding) is a manufacturing process for producing parts by injecting molten material into a mould, or mold. Injection moulding can be performed with a host of materials mainly including metals (for ...
*
Airbrush An airbrush is a small, air-operated tool that atomizes and sprays various media, most often paint, but also ink, dye, and make-up. Spray painting developed from the airbrush and is considered to employ a type of airbrush. History Up unt ...
ing used by model railroaders and other hobbyists to paint and weather cars, boats, planes and trains * Food and beverage capping and
fermentation Fermentation is a type of anaerobic metabolism which harnesses the redox potential of the reactants to make adenosine triphosphate (ATP) and organic end products. Organic molecules, such as glucose or other sugars, are catabolized and reduce ...
* Compressed air from Lysefjorden/ Preikestolen (Norway) is being sold in cans, mostly to China.


Emergency services and firefighting

* Self-Contained Breathing Apparatus (
SCBA A self-contained breathing apparatus (SCBA) is a respirator worn to provide an autonomous supply of breathable gas in an atmosphere that is immediately dangerous to life or health from a gas cylinder. They are typically used in firefighting a ...
) – Used by firefighters, rescue workers, and hazmat teams for breathing in hazardous environments. *
Fire Suppression Systems Fire suppression systems are used to extinguish, control, or in some cases, entirely prevent fires from spreading or occurring. Fire suppression systems have an incredibly large variety of applications, and as such, there are many different types ...
– Some fire suppression systems, such as dry chemical and CO₂ systems, use compressed air to discharge fire-extinguishing agents. * Rescue Tools (Pneumatic Jaws of Life) – Hydraulic or pneumatic-powered rescue tools used to cut through vehicles and debris during emergency extrications. * Inflatable Rescue Devices – Air-powered inflatable boats, flotation devices, and emergency life rafts.


Medical

*
Ventilator A ventilator is a type of breathing apparatus, a class of medical technology that provides mechanical ventilation by moving breathable air into and out of the lungs, to deliver breaths to a patient who is physically unable to breathe, or breathi ...
s and
Respirator A respirator is a device designed to protect the wearer from inhaling hazardous atmospheres including lead, lead fumes, vapors, gases and particulate matter such as dusts and airborne pathogens such as viruses. There are two main categories o ...
s – Compressed air is used in hospitals and ambulances to power ventilators and oxygen delivery systems. * Dental Equipment – Dentists use compressed air to power drills and cleaning tools *
Hyperbaric chamber A diving chamber is a vessel for human occupation, which may have an entrance that can be sealed to hold an internal pressure significantly higher than ambient pressure, a pressurised gas system to control the internal pressure, and a supply of ...
s – Used for treating decompression sickness, wound healing, and other medical conditions requiring high-pressure oxygen therapy. * Portable Oxygen Systems – Some emergency and home healthcare oxygen systems use compressed air for efficient delivery.


Energy Costs of a Compressed Air System

Regarding operating costs, it is important to consider that compressed air represents a significant portion of total energy costs. Roughly, every 1 kW of power produced requires 8 kW of electrical power. Additionally, considering the lifecycle of a compressed air system (about 10–15 years), the total costs can be broken down as follows: * 70–75%: Energy costs * 15–20%: Compressor, accessories, piping, and installation costs * 10%: Maintenance costs


Design of systems

Compressor rooms must be designed with ventilation systems to remove
waste heat Waste heat is heat that is produced by a machine, or other process that uses energy, as a byproduct of doing work. All such processes give off some waste heat as a fundamental result of the laws of thermodynamics. Waste heat has lower utility ...
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 Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation (meteorology), precipitation, dew, or fog t ...
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 ; 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 . Breathing gases Gas technologies Energy storage Industrial gases Pneumatics Respiration