Editing Air compressor

{{short description|Machine to pressurize air}}
[[File:AirCompressorHusky.JPG|thumb|Air compressor supplies air into a [[nail gun]].]]
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 [[Pneumatics|pneumatic]] device that [[energy conversion|converts mechanical power]] (from an [[electric motor]], [[Diesel engine|diesel]] or [[gasoline engine]], etc.) 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.<ref>{{Cite news|url=http://www.popularmechanics.com/home/how-to/a151/how-air-compressors-work/|title=How Do Air Compressors Work?|date=2015-03-18|newspaper=Popular Mechanics|access-date=2017-01-12}}</ref> 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.

==Classification==
===Power source===
*Internal combustion engine: Petrol, petrol without oil, diesel
*Electric: AC, DC

===Drive type===
*Direct drive
*Belt drive

Compressors may be classified according to the pressure delivered:
* Low-pressure air compressors, which have a discharge pressure of {{convert|150|psi|bar}} or less<ref name="Classification">{{Cite web |title=Classification of air compressors |url=http://www.tpub.com/fireman/102.htm |access-date=2017-01-12 |website=www.tpub.com}}</ref>
* Medium-pressure compressors which have a discharge pressure of {{convert|151 to 1,000|psi|bar}}<ref name="Classification" />
* High-pressure air compressors, which have a discharge pressure above {{convert|1,000|psi|bar}}<ref name="Classification" />

There are numerous methods of air compression, divided into either positive-displacement or roto-dynamic types.<ref>{{cite web|title=Air Compressor Types and Controls|url=http://www.nrcan.gc.ca/energy/products/reference/14970|website=Natural Resources Canada|date=4 February 2014 }}</ref>
* Single-stage [[reciprocating compressor]]
* Multi-stage reciprocating compressor<ref>{{Cite web |last=Davis |first=Jeff |date=2022-02-23 |title=What is a Two Stage Air Compressor – Air Compressor Insider |url=https://aircompressorinsider.com/what-is-a-two-stage-air-compressor/ |access-date=2023-07-26 |language=en-US}}</ref>
* [[Rotary-screw compressor|Single stage rotary-screw compressor]]
* Two-stage rotary screw compressor
* [[Rotary vane pump]]
* [[Scroll compressor]]
* [[Centrifugal compressor|Centrifugal (roto-dynamic or turbo) compressor]]
* [[Axial compressor]], often used in [[jet engine]]s.
* Another way of classification, is by lubrication type: oil lubricated and oil-free. The oil-less (or oil-free) system has more technical development such as they do not require oil for lubrication. oil-less air compressors are also lighter and more portable than oil-lubricated models but require more maintenance. On other side Oil-lubricated air compressors are the more traditional type of air compressor. They require oil to lubricate the motor which helps prolong the compressor's life. One of the benefits of oil-lubricated compressors is that they tend to be more durable and require less maintenance than oil-free compressors.[https://compressorvenue.com/oil-vs-oil-free-air-compressors/]{{dead link|date=May 2025|bot=medic}}{{cbignore|bot=medic}}

===Positive displacement compressors===

Positive-displacement compressors work by forcing air through a chamber whose volume is decreased to compress the air. Once the pressure is greater than the pressure outside the discharge [[valve]], a port or valve opens and air is discharged into the outlet system from the compression chamber.<ref>{{Cite news|url=http://www.thecompressedairblog.com/compressor-selection-basics-positive-displacement-versus-dynamic-compression/|title=Compressor Selection Basics: Positive Displacement versus Dynamic Compression|access-date=2017-01-12|via=The 5th Utility}}</ref> Common types of positive displacement compressors are
[[File:Two-Stage_Air_Compressor_assembled_on_a_vertical_tank_and_equipped_with_a_Joule-Thomson_(JT)_type_refrigerated_compressed_air_dryer.jpg|thumb|Technical illustration of a two-stage air compressor]]
[[File:Portable_Single_Stage_Air_Compressor.jpg|thumb|Technical illustration of a portable single-stage air compressor]]
* Piston-type air compressors, which compress air by pumping it through cylinders by reciprocating pistons. They use one-way valves to admit air into the cylinder on the induction stroke and prevent it from leaving by the same route, and out of the cylinder through the exhaust valve to the high pressure side on the compression stroke, again using a non-return valve to prevent it leaking back on the next induction stroke. Piston compressors can be single or multi-stage, and may also have one or more sets of cylinders in parallel (at the same pressure). Multi-stage compressors provide greater efficiency than their single-stage counterparts for high compression ratios, and generally use interstage cooling to improve efficiency.

The capacities for both single-stage and two-stage compressors are generally specified in [[Standard cubic feet per minute|Standard Cubic feet per Minute]] (SCFM)  or litres per minute and [[Pounds per square inch|pounds per square Inch]] (PSI) or bar.  To a lesser extent, some compressors are rated in [[actual cubic feet per minute]] (ACFM).{{clarify|date=June 2023}}{{citation needed|date=June 2023}}  Still others are rated in [[cubic feet per minute]] (CFM).{{clarify|date=June 2023}}{{citation needed|date=June 2023}} Using CFM alone to rate a compressor is ambiguous because it represents a flow rate without a pressure reference. i.e. 20 CFM ''at 60 PSI.''

Single stage compressors usually fall into the fractional through 5 [[horsepower]] range.{{citation needed|date=June 2023}} Two-stage compressors normally fall into the 5 through 30 [[horsepower]] range.{{citation needed|date=June 2023}}{{clarify|Is this multi-stage or multi cylinder?|date=June 2023}}

* [[Rotary-screw compressor|Rotary screw compressors]] provide positive-displacement compression by matching two helical screws that, when turned, guide air into a chamber, whose volume is decreased as the screws turn. Rotary screw compressors can be single-stage or two-stage.{{clarify|date=June 2023}}
* [[Rotary vane pump|Vane compressors]]: use a slotted rotor with varied blade placement{{clarify|date=June 2023}} to guide air into a chamber and compress the volume. This type of compressor delivers a fixed volume of air at high pressures.{{clarify|date=June 2023}}

=== Roto-dynamic or turbo compressors ===
Roto-dynamic air compressors include [[centrifugal compressor]]s where Rotating vanes impart kinetic energy to a gas and stationary passages convert velocity into a rise in pressure, and [[axial compressor]]s, where rotor blades impart the kinetic energy and stator blades convert it to a rise in pressure.

== Cooling ==
Due to [[adiabatic heating#Adiabatic heating and cooling|adiabatic heating]], air compressors require some method of disposing of [[waste heat]].  Generally this is some form of [[Air cooling|air-]] or water-cooling, although some (particularly rotary type) compressors may be cooled by oil (that is then in turn air- or water-cooled).<ref>{{cite web|url=http://www.engineeringtoolbox.com/air-compressor-types-d_441.html|title=Types of Air Compressors|website=The Engineering ToolBox}}</ref> The atmospheric changes are also considered during cooling of compressors.{{clarify|What atmospheric changes?|date=June 2023}} The type of cooling is determined by considering the factors such as inlet temperature, ambient temperature, power of the compressor and area of application. There is no single type of compressor that could be used for any application.

== Applications ==
{{Main|Compressed air}}
[[File:CompAir Fahrbarer Kompressor Typ C38.jpg|thumb|Portable diesel powered air compressor for powering tools, such as [[jackhammer]]s]]
Air compressors have many uses, such as supplying clean high-pressure air to fill [[gas cylinder]]s, supplying clean moderate-pressure air to a submerged [[Surface-supplied diving|surface supplied air diver]], supplying moderate-pressure clean air for driving some office and school building [[pneumatic]] [[HVAC control system]] valves, supplying a large amount of moderate-pressure air to power [[pneumatic tool]]s, such as [[jackhammer]]s, filling [[Pressure vessel|high pressure air tanks]] (HPA, air tank), for filling [[tire]]s, blown fibre installation and to produce large volumes of moderate-pressure air for large-scale industrial processes (such as oxidation for petroleum coking or cement plant bag house purge systems).<ref>{{Cite web|url=http://www.industry.siemens.com/topics/global/en/pumps-fans-compressors/compressor-drives/applications-for-compressors/pages/default.aspx|title=Applications for Compressors|website=www.industry.siemens.com|language=en|access-date=2017-01-12}}</ref>

Air compressors are also widely used in oil and gas, mining and drilling applications as the flushing medium, aerating muds in underbalanced drilling and in air pigging of pipelines.

Most air compressors either are reciprocating piston type, rotary vane or [[rotary screw compressor|rotary screw]]. [[Centrifugal compressors]] are common in very large applications, while rotary screw, scroll,<ref>{{cite web |last1=Hislop |first1=Reid |title=Plug Power Places Large Production Order for Air Squared Compressors to be used in GenDrive Fuel Cell Units |url=https://s21.q4cdn.com/824959975/files/doc_news/PLUG-POWER-PLACES-LARGE-PRODUCTION-ORDER-FOR-AIR-SQUARED-COMPRESSORS-TO-BE-USED-IN-GENDRIVE-FUEL-CELL-UNITS.pdf |website=Plug Power |access-date=10 May 2019}}</ref> and reciprocating air compressors are favoured for small and medium-sized applications.

== Power source ==
Air compressors are designed to utilize a variety of power sources. While direct drive gasoline or diesel-engines and electric motors are among the most popular, air compressors that utilize vehicle engines, [[Power take-off|power-take-off]], or hydraulic ports are also commonly used in mobile applications.<ref>{{Cite news|date=2018-10-16|title=Easy Guide To Rotary Screw Air Compressors For Vehicles – By VMAC|language=en-US|work=VMAC|url=https://www.vmacair.com/blog/easy-guide-to-rotary-screw-air-compressors-for-trucks-vans/|access-date=2018-10-30}}</ref>

The power of a compressor is measured in HP ([[horsepower]]) and CFM ([[cubic foot|cubic feet per minute]] of intake air).<ref>{{cite web|url=http://www.truetex.com/aircompressors.htm|title=Evaluating True Horsepower and CFM Ratings of Air Compressors}}</ref>
The volume of the pressure vessel and the stored pressure indicate the volume of compressed air (in reserve) available.

Gasoline and diesel-powered compressors are widely used in remote areas with problematic access to electricity. They are noisy and require ventilation for exhaust gases, particularly if the compressed air is to be used for a breathing air supply. Electric-powered compressors are widely used in production, workshops and garages with permanent access to electricity. Common workshop/garage compressors are 110-120 Volt or 230-240 Volt. Compressor tank shapes are: "pancake", "twin tank", "horizontal", and "vertical". Depending on a size and purpose compressors can be stationary or portable.

== Maintenance ==
[[File:Niger, Kodo (9), tire repair shop.jpg|thumb|A small air compressor in use at a roadside tire repair shop in the village of Kodo, Niger]]
To ensure all compressor types run efficiently with no leaks, it is necessary to perform routine maintenance. The cost of maintenance only accounts for 8% of the life cycle cost of owning an air compressor.<ref>{{cite web|url=https://aircompressoruniverse.com/how-many-watts-does-an-air-compressor-use/|title=How Many Watts Does An Air Compressor Use|date=11 August 2023 }}</ref>

==Air compressor isentropic efficiency==
According to [[Compressed Air and Gas Institute|CAGI]] air compressor performance verification data sheets, the higher the isentropic efficiency is, the better the energy saving is. The better air compressor isentropic efficiency has reached 95%.
<ref name="CAGI Performance Verification Data Sheets">[https://www.cagi.org/performance-verification/data-sheets.aspx CAGI Performance Verification Data Sheets] {{webarchive|url=https://web.archive.org/web/20220121211200/https://www.cagi.org/performance-verification/data-sheets.aspx}}.</ref>

Approximately 70~80% of the air compressor's total lifetime cost is energy consumption, so using the high-efficiency air compressor is one of the energy-saving methods.{{citation needed|date=June 2023}}

==See also==
* [[Vacuum pump]]
* [[Free-piston engine]]
* [[Gas compressor]]
* [[Pneumatics]]
* [[Gas cylinder]]
* "[[The Blue Air Compressor]]"

==References==
{{Commons category}}
{{Reflist}}

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[[Category:Gas compressors]]
[[Category:Gases]]
[[Category:Diving support equipment]]
[[Category:Gas technologies]]
[[Category:Industrial gases]]