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An air compressor is a
pneumatic 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 ...
device that converts power (using an
electric motor An electric motor is an electrical machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a wire winding to generate f ...
,
diesel Diesel may refer to: * Diesel engine, an internal combustion engine where ignition is caused by compression * Diesel fuel, a liquid fuel used in diesel engines * Diesel locomotive, a railway locomotive in which the prime mover is a diesel engi ...
or gasoline engine, etc.) into
potential energy In physics, potential energy is the energy held by an object because of its position relative to other objects, stresses within itself, its electric charge, or other factors. Common types of potential energy include the gravitational potenti ...
stored in pressurized air (i.e., compressed air). By one of several methods, an air compressor forces more and more air into a storage tank, increasing the pressure. When the tank's pressure reaches its engineered upper limit, the air compressor shuts off. The compressed air, then, is held in the tank until called into use. The kinetic energy provided by the compressed air can be used for a variety of applications such as
pneumatic tool 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 compressed carbon dioxide () stored in small cylinders ...
as it is released air and the tank depressurizes. When tank pressure reaches its lower limit, the air compressor turns on again and re-pressurizes the tank. An air compressor must be differentiated from a pump because it works for any gas/air, while pumps work on a liquid.


Classification

Compressors may be classified according to the pressure delivered: # Low-pressure air compressors (LPACs), which have a discharge pressure of or lessreciprocating compressor 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 c ...
# Multi-stage reciprocating compressor # Compound compressor # Single stage rotary-screw compressor #Two-stage rotary screw compressor # Rotary vane pump #
Scroll compressor A scroll compressor (also called ''spiral compressor'', scroll pump and scroll vacuum pump) is a device for compressing air or refrigerant. It is used in air conditioning equipment, as an automobile supercharger (where it is known as a scroll- ...
# Centrifugal (roto-dynamic or turbo) compressor In another way of classification, there are two main types of air-compressors: oil-injected and oil-less. The oil-less (or Oil-Free) system has more technical development and delivers air of better quality for critical applications where oil contamination cannot be tolerated (such as food and medicine production) although it is more expensive, louder and lasts for less time than oil-lubed pumps. There are numerous methods of air compression, divided into either positive-displacement or roto-dynamic types. # Medium-pressure compressors which have a discharge pressure of # High-pressure air compressors (HPACs), which have a discharge pressure above


Positive displacement compressors

Positive-displacement compressors work by forcing air in a chamber whose volume is decreased to compress the air. Once the maximum pressure is reached, a port or valve opens and air is discharged into the outlet system from the compression chamber. Common types of positive displacement compressors are * Piston-type: air compressors use this principle by pumping air into an air chamber through the use of the constant motion of pistons. They use one-way valves to guide air into and out of a chamber whose base consists of a moving piston. When the piston is on its down stroke, it draws air into the chamber. When it is on its up stroke, the charge of air is forced out and into a storage tank. Piston compressors generally fall into two basic categories, single-stage and two-stage. Single stage compressors usually fall into the fractional through 5
horsepower Horsepower (hp) is a unit of measurement of power, or the rate at which work is done, usually in reference to the output of engines or motors. There are many different standards and types of horsepower. Two common definitions used today are t ...
range. Two-stage compressors normally fall into the 5 through 30 horsepower range. Two-stage compressors provide greater efficiency than their single-stage counterparts. For this reason, these compressors are the most common units within the small business community. The capacities for both single-stage and two-stage compressors is generally provided in horsepower (HP), Standard Cubic feet per Minute (SCFM)* and
Pounds per Square Inch The pound per square inch or, more accurately, pound-force per square inch (symbol: lbf/in2; abbreviation: psi) is a unit of pressure or of stress based on avoirdupois units. It is the pressure resulting from a force of one pound-force applied t ...
(PSI). *To a lesser extent, some compressors are rated in
Actual Cubic Feet per Minute Actual cubic feet per minute (ACFM) is a unit of volumetric flow. It is commonly used by manufacturers of blowers and compressors. This is the actual gas delivery with reference to inlet conditions, whereas cubic foot per minute (CFM) is an unqua ...
(ACFM). Still others are rated in Cubic Feet per Minute (CFM). Using CFM to rate a compressor is incorrect because it represents a flow rate that is independent of a pressure reference. i.e. 20 CFM ''at 60 PSI.'' * Rotary screw compressors: use 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 * Vane compressors: use a slotted rotor with varied blade placement to guide air into a chamber and compress the volume. This type of compressor delivers a fixed volume of air at high pressures.


Roto-dynamic or turbo compressors

Roto-dynamic air compressors include centrifugal compressors and axial compressors. Rotating vanes impart kinetic energy to a gas and stationary passages convert velocity into a rise in pressure.


Cooling

Due to adiabatic heating, air compressors require some method of disposing of
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 utilit ...
. Generally this is some form of air- or water-cooling, although some (particularly rotary type) compressors may be cooled by oil (that is then in turn air- or water-cooled). The atmospheric changes are also considered during cooling of compressors. 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

Air compressors have many uses, including: supplying high-pressure clean air to fill
gas cylinder A gas cylinder is a pressure vessel for storage and containment of gases at above atmospheric pressure. High-pressure gas cylinders are also called ''bottles''. Inside the cylinder the stored contents may be in a state of compressed gas, vap ...
s, supplying moderate-pressure clean air to a submerged surface supplied diver, supplying moderate-pressure clean air for driving some office and school building
pneumatic 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 ...
HVAC control system valves, supplying a large amount of moderate-pressure air to power
pneumatic tool 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 compressed carbon dioxide () stored in small cylinders ...
s, such as jackhammers, filling high pressure air tanks (HPA, air tank), for filling
tire A tire (American English) or tyre (British 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 (engineering), t ...
s, 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). 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. Centrifugal compressors are common in very large applications, while rotary screw, scroll, and reciprocating air compressors are favored for small and medium sized applications.


Driver options

Air compressors are designed to utilize a variety of power sources. While gas/diesel-powered and electric air compressors are among the most popular, air compressors that utilize vehicle engines, power-take-off, or hydraulic ports are also commonly used in mobile applications. The power of a compressor is measured in HP (
horsepower Horsepower (hp) is a unit of measurement of power, or the rate at which work is done, usually in reference to the output of engines or motors. There are many different standards and types of horsepower. Two common definitions used today are t ...
) and CFM ( cubic feet per minute of intake air). The gallon size of the tank specifies the volume of compressed air (in reserve) available. Gas/diesel powered compressors are widely used in remote areas with problematic access to electricity. They are noisy and require ventilation for exhaust gases. 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

To ensure all compressor types run efficiently with no leaks, it is imperative to perform routine maintenance, such as monitoring and replacing air fuel management components and lubricant maintenance as well as draining water from the tank and replacing seals. Most air compressors can be operated by following the instructions from the included manual. It is suggested that air compressor owners perform daily inspections of their equipment, such as: * Checking for oil and air leaks * Checking the differential pressure in the compressed air filter * Determining whether or not the oil in the compressor should be changed * Verifying safe operating temperature * Draining
condensation Condensation is the change of the state of matter from the gas phase into the liquid phase, and is the reverse of vaporization. The word most often refers to the water cycle. It can also be defined as the change in the state of water vapo ...
from air receiver tanks


Air compressor isentropic efficiency

According to 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%. CAGI Performance Verification Data Sheets
.
Approximately 70~80% of the air compressor total life time cost is energy consumption, so using the high efficiency air compressor is one of energy saving methods.


See also

*
Vacuum pump A vacuum pump is a device that draws gas molecules from a sealed volume in order to leave behind a partial vacuum. The job of a vacuum pump is to generate a relative vacuum within a capacity. The first vacuum pump was invented in 1650 by Otto ...
* Free-piston engine * Gas compressor * Pneumatics *
Gas cylinder A gas cylinder is a pressure vessel for storage and containment of gases at above atmospheric pressure. High-pressure gas cylinders are also called ''bottles''. Inside the cylinder the stored contents may be in a state of compressed gas, vap ...


External links


CAGI Isentropic Efficiency


References

{{Authority control Gas compressors Gases Diving support equipment Gas technologies Industrial gases