This article is about air under pressure. For canisters inaccurately marketed as "compressed air", see Gas duster.
Compressed air is air kept under a pressure that is greater than atmospheric pressure. Compressed air is an important medium for transfer of energy in industrial processes, and is used for power tools 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. It may be carried by the diver in a high-pressure diving cylinder, or supplied from the surface at lower pressure through an air line or diver's umbilical.[1] 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 hours consumption per year.[2][3]
Industrial use of piped compressed air for power transmission was developed in the mid-19th century; unlike 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 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 invented air brakes for trains starting in 1869; these brakes considerably improved the safety of rail operations.[4] 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 could directly obtain compressed air from the force of falling water.[5]
Breathing
Air for breathing may be stored at high pressure and gradually released when needed, as in scuba diving, or produced continuously to meet requirements, as in 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. 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.[6]
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 bells 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 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. Many workers were killed by the disease on projects such as the Brooklyn Bridge and the 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.[7]
Air under moderately high pressure, such as is used when diving below about 20 metres (70ft), has an increasing narcotic effect on the nervous system. Nitrogen narcosis is a hazard when diving. For diving much beyond 30 metres (100ft), it is less safe to use air alone and special breathing mixes containing helium are often used.[8]
Uses
Air compressor station in a power plant
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.[9]
Technical Illustration of portable single-stage air compressorTwo-stage air compressor assembled on a horizontal tank and equipped with a Joule-Thomson (JT) type refrigerated compressed air dryer
Compressed air is used for many purposes, including:
Pneumatics, the use of pressurized gases to do work
Pneumatic post, using capsules to move paper and small goods through tubes.
Compressed air from Lysefjorden/Preikestolen (Norway) is being sold in cans, mostly to China.[11]
Design of systems
Compressor rooms must be designed with ventilation systems to remove waste heat produced by the compressors.[12]
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.[13] After compressed air cools, then the vaporized water turns to liquefied water.[14][15]
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.[16]
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.[17] 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,[18] or due to turbulence at pipe fittings.[19]
Compressor– Machine to increase pressure of gas by reducing its volume
Gas duster– Product used for cleaning or dusting sensitive devices that cannot be cleaned using water – (generally use fluorocarbons but some use compressed air.)
↑ Lance Day, Ian McNeil (ed.), Biographical Dictionary of the History of Technology, Routledge, 2002, ISBN1134650205, p. 1294
↑ Peter Darling (ed.), SME Mining Engineering Handbook, Third Edition Society for Mining, Metallurgy, and Exploration (U.S.) 2011, ISBN0873352645, p. 705
↑ U.S. Navy Supervisor of Diving (2008). U.S. Navy Diving Manual(PDF). SS521-AG-PRO-010, revision 6. U.S. Naval Sea Systems Command. Archived from the original(PDF) on 2014-12-10. Retrieved 2014-01-21.
↑ E. Hugh Snell, Compressed Air Illness Or So-called Caisson DiseaseH. K. Lewis, 1896 pp.
↑ Bennett, Peter; Rostain, Jean Claude (2003). "Inert Gas Narcosis". In Brubakk, Alf O; Neuman, Tom S (eds.). Bennett and Elliott's physiology and medicine of diving (5thed.). United States: Saunders. ISBN0-7020-2571-2. OCLC51607923.
↑ Yuan, C., Zhang, T., Rangarajan, A., Dornfeld, D., Ziemba, B., and Whitbeck, R. “A Decision-based Analysis of Compressed Air Usage Patterns in Automotive Manufacturing”, Journal of Manufacturing Systems, 25 (4), 2006, pp.293-300
A compressed-air car is a compressed-air vehicle powered by pressure vessels filled with compressed air. It is propelled by the release and expansion of the air within a motor adapted to compressed air. The car might be powered solely by air, or combined with other fuels such as gasoline, diesel, or an electric plant with regenerative braking.
Pneumatics is a branch of engineering that makes use of gas or pressurized air.
An air compressor is a machine that takes ambient air from the surroundings and discharges it at a higher pressure. It is an application of a gas compressor and a pneumatic device that converts mechanical power into potential energy stored in compressed air, which has many uses. A common application is to compress air into a storage tank, for immediate or later use. When the delivery pressure reaches its set upper limit, the compressor is shut off, or the excess air is released through an overpressure valve. The compressed air is stored in the tank until it is needed. The pressure energy provided by the compressed air can be used for a variety of applications such as pneumatic tools as it is released. When tank pressure reaches its lower limit, the air compressor turns on again and re-pressurizes the tank. A compressor is different from a pump because it works on a gas, while pumps work on a liquid.
Saturation diving is diving for periods long enough to bring all tissues into equilibrium with the partial pressures of the inert components of the breathing gas used. It is a diving mode that reduces the number of decompressions divers working at great depths must undergo by only decompressing divers once at the end of the diving operation, which may last days to weeks, having them remain under pressure for the whole period. A diver breathing pressurized gas accumulates dissolved inert gas used in the breathing mixture to dilute the oxygen to a non-toxic level in the tissues, which can cause decompression sickness if permitted to come out of solution within the body tissues; hence, returning to the surface safely requires lengthy decompression so that the inert gases can be eliminated via the lungs. Once the dissolved gases in a diver's tissues reach the saturation point, however, decompression time does not increase with further exposure, as no more inert gas is accumulated.
Fluid power is the use of fluids under pressure to generate, control, and transmit power. Fluid power is conventionally subdivided into hydraulics and pneumatics. Although steam is also a fluid, steam power is usually classified separately from fluid power. Compressed-air and water-pressure systems were once used to transmit power from a central source to industrial users over extended geographic areas; fluid power systems today are usually within a single building or mobile machine.
A compressor is a mechanical device that increases the pressure of a gas by reducing its volume. An air compressor is a specific type of gas compressor.
A diving air compressor is a breathing air compressor that can provide breathing air directly to a surface-supplied diver, or fill diving cylinders with high-pressure air pure enough to be used as a hyperbaric breathing gas. A low pressure diving air compressor usually has a delivery pressure of up to 30 bar, which is regulated to suit the depth of the dive. A high pressure diving compressor has a delivery pressure which is usually over 150 bar, and is commonly between 200 and 300 bar. The pressure is limited by an overpressure valve which may be adjustable.
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.
Gas blending for scuba diving is the filling of diving cylinders with non-air breathing gases such as nitrox, trimix and heliox. Use of these gases is generally intended to improve overall safety of the planned dive, by reducing the risk of decompression sickness and/or nitrogen narcosis, and may improve ease of breathing.
A reciprocating compressor or piston compressor is a positive-displacement compressor that uses pistons driven by a crankshaft to deliver gases at high pressure. Pressures of up to 5,000 PSIG are commonly produced by multistage reciprocating compressors.
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 to operate many other pneumatic systems.
In geotechnical engineering, a caisson is a watertight retaining structure used, for example, to work on the foundations of a bridge pier, for the construction of a concrete dam, or for the repair of ships.
An air brake or, more formally, a compressed-air-brake system, is a type of friction brake for vehicles in which compressed air pressing on a piston is used to both release the parking/emergency brakes in order to move the vehicle, and also to apply pressure to the brake pads or brake shoes to slow and stop the vehicle. Air brakes are used in large heavy vehicles, particularly those having multiple trailers which must be linked into the brake system, such as trucks, buses, trailers, and semi-trailers, in addition to their use in railroad trains. George Westinghouse first developed air brakes for use in railway service. He patented a safer air brake on March 5, 1872. Westinghouse made numerous alterations to improve his air pressured brake invention, which led to various forms of the automatic brake. In the early 20th century, after its advantages were proven in railway use, it was adopted by manufacturers of trucks and heavy road vehicles.
The breathing performance of regulators is a measure of the ability of a breathing gas regulator to meet the demands placed on it at varying ambient pressures and temperatures, and under varying breathing loads, for the range of breathing gases it may be expected to deliver. Performance is an important factor in design and selection of breathing regulators for any application, but particularly for underwater diving, as the range of ambient operating pressures and temperatures, and variety of breathing gases is broader in this application. A diving regulator is a device that reduces the high pressure in a diving cylinder or surface supply hose to the same pressure as the diver's surroundings. It is desirable that breathing from a regulator requires low effort even when supplying large amounts of breathing gas as this is commonly the limiting factor for underwater exertion, and can be critical during diving emergencies. It is also preferable that the gas is delivered smoothly without any sudden changes in resistance while inhaling or exhaling, and that the regulator does not lock up and either fail to supply gas or free-flow. Although these factors may be judged subjectively, it is convenient to have standards by which the many different types and manufactures of regulators may be objectively compared.
A hydraulic compressor is a type of compressor that is designed to convert hydraulic power to pneumatic power. It is used across various industries to improve the efficiency of certain types of machinery. Hydraulic compressors have a hydraulic pump to push air through a pipe, which forces a motor to spin. The motor powers the internal air compressor, releasing air in a chamber as a result. Compressors became more popularized in 1799 when Englishman George Medhurst invented a motorized air compressor as a means for propulsion. They have technologically advanced to the point where they can achieve greater force and precision than humans.
A booster pump is a machine which increases the pressure of a fluid. It may be used with liquids or gases, and the construction details vary depending on the fluid. A gas booster is similar to a gas compressor, but generally a simpler mechanism which often has only a single stage of compression, and is used to increase pressure of a gas already above ambient pressure. Two-stage boosters are also made. Boosters may be used for increasing gas pressure, transferring high pressure gas, charging gas cylinders and scavenging.
Compressed air dryers are special types of filter systems that are specifically designed to remove the water that is inherent in compressed air. The compression of air raises its temperature and concentrates atmospheric contaminants, primarily water vapor, as resulting in air with elevated temperature and 100% relative humidity. As the compressed air cools down, water vapor condenses into the tank(s), pipes, hoses and tools connected downstream from the compressor which may be damaging. Therefore water vapor is removed from compressed air to prevent condensation from occurring and to prevent moisture from interfering in sensitive industrial processes.
The following index is provided as an overview of and topical guide to underwater diving:
Diving support equipment is the equipment used to facilitate a diving operation. It is either not taken into the water during the dive, such as the gas panel and compressor, or is not integral to the actual diving, being there to make the dive easier or safer, such as a surface decompression chamber. Some equipment, like a diving stage, is not easily categorised as diving or support equipment, and may be considered as either.
A built-in breathing system is a source of breathing gas installed in a confined space where an alternative to the ambient gas may be required for medical treatment, emergency use, or to minimise a hazard. They are found in diving chambers, hyperbaric treatment chambers, and submarines.
This page is based on this Wikipedia article Text is available under the CC BY-SA 4.0 license; additional terms may apply. Images, videos and audio are available under their respective licenses.
