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An air compressor is a device that converts power (usually from an electric motor, a diesel

engine or a gasoline engine) into kinetic energy by compressing and pressurizing air, which, on

command, can be released in quick bursts. There are numerous methods of air compression,divided into either positive-displacement or negative-displacement types.

[1][2]

Types of air compressor:

1. According to the design and principle of operation1. Reciprocating compressor2. Rotary compressor

2. According to the number of stages1. Single stage compressor2. Multi stage compressor

3. According to the pressure limits1. Low pressure compressors2. Medium pressure compressors3.

High pressure compressors4. Super high pressure compressors

4. According to the capacity1. Low capacity compressors2. Medium capacity compressors3. High capacity compressors

5. According to the method of cooling1. Air cooled compressor2. Water cooled compressor

Positive-displacement air compressors work by forcing air into a chamber whose volume is

reduced to compress the air. Piston-type air compressors use this principle by pumping air intoan air chamber through the use of the constant motion of pistons. They use unidirectional valvesto guide air into a chamber, where the air is compressed.

[1]Rotary screw compressors also use

positive-displacement compression by matching two helical screws that, when turned, guide air

into a chamber, the volume of which is reduced as the screws turn. Vane compressors use aslotted rotor with varied blade placement to guide air into a chamber and compress the volume.

Negative-displacement air compressors include centrifugal compressors. These devices usecentrifugal force generated by a spinning impeller to accelerate and then decelerate captured air,

which pressurizes it.[1]

Conventional air compressors are used in several different applications:

To supply high-pressure clean air to fillgas cylinders To supply moderate-pressure clean air to a submergedsurface supplied diver To suppy moderate-pressure clean air for driving some office and school building

pneumaticHVAC control systemvalves

To supply a large amount of moderate-pressure air to powerpneumatic tools For fillingtires

http://en.wikipedia.org/wiki/Air_compressor#cite_note-PM-0http://en.wikipedia.org/wiki/Air_compressor#cite_note-PM-0http://en.wikipedia.org/wiki/Air_compressor#cite_note-PM-0http://en.wikipedia.org/wiki/Air_compressor#cite_note-PM-0http://en.wikipedia.org/wiki/Air_compressor#cite_note-PM-0http://en.wikipedia.org/wiki/Air_compressor#cite_note-PM-0http://en.wikipedia.org/wiki/Air_compressor#cite_note-PM-0http://en.wikipedia.org/wiki/Air_compressor#cite_note-PM-0http://en.wikipedia.org/wiki/Air_compressor#cite_note-PM-0http://en.wikipedia.org/wiki/Gas_cylinderhttp://en.wikipedia.org/wiki/Gas_cylinderhttp://en.wikipedia.org/wiki/Gas_cylinderhttp://en.wikipedia.org/wiki/Surface_supplied_divinghttp://en.wikipedia.org/wiki/Surface_supplied_divinghttp://en.wikipedia.org/wiki/Surface_supplied_divinghttp://en.wikipedia.org/wiki/Pneumatichttp://en.wikipedia.org/wiki/HVAC_control_systemhttp://en.wikipedia.org/wiki/HVAC_control_systemhttp://en.wikipedia.org/wiki/HVAC_control_systemhttp://en.wikipedia.org/wiki/Pneumatic_toolhttp://en.wikipedia.org/wiki/Pneumatic_toolhttp://en.wikipedia.org/wiki/Pneumatic_toolhttp://en.wikipedia.org/wiki/Tirehttp://en.wikipedia.org/wiki/Tirehttp://en.wikipedia.org/wiki/Tirehttp://en.wikipedia.org/wiki/Tirehttp://en.wikipedia.org/wiki/Pneumatic_toolhttp://en.wikipedia.org/wiki/HVAC_control_systemhttp://en.wikipedia.org/wiki/Pneumatichttp://en.wikipedia.org/wiki/Surface_supplied_divinghttp://en.wikipedia.org/wiki/Gas_cylinderhttp://en.wikipedia.org/wiki/Air_compressor#cite_note-PM-0http://en.wikipedia.org/wiki/Air_compressor#cite_note-PM-0http://en.wikipedia.org/wiki/Air_compressor#cite_note-PM-0http://en.wikipedia.org/wiki/Air_compressor#cite_note-PM-0

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To produce large volumes of moderate-pressure air for macroscopic industrial processes(such as oxidation for petroleum coking or cement plant bag house purge systems).

Most air compressors are either reciprocating piston type, rotary vane orrotary screw.

Centrifugal compressors are common in very large applications. There are two main types of air

compressor's pumps: Oil lubed and oil-less. The oil-less system has more technical development,but they are more expensive, louder and last for less time than the oiled lube pumps. However,

the air delivered has better quality.

air compressors used in a wide range of situationsfrom corner gas stations to majormanufacturing plants. And, more and more, air compressors are finding their way into home

workshops, basements and garages. Models sized to handle every job, from inflating pool toys to

powering tools such as nail guns, sanders, drills, impact wrenches, staplers and spray guns are

now available through local home centers, tool dealers and mail-order catalogs.

The big advantage of air power is that each tool doesn't need its own bulky motor. Instead, a

single motor on the compressor converts the electrical energy into kinetic energy. This makes for

light, compact, easy-to-handle tools that run quietly and have fewer parts that wear out.

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Air compressor typesReciprocating (Piston) Air Compressor

A reciprocating air compressor makes use of piston(s) to compress air and store it in a storage tank.

Based on the number of compression stages, reciprocating compressor can be a single-stage or double-

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stage configuration. In the single-stage unit, only one piston is used to compress air, whereas there are

two pistons for air compression in the double-stage air compressor.

Rotary Air Compressor

A rotary air compressor is similar to the positive displacement configuration of a reciprocating

compressor. Over here, two spinning helical screws or rotors are involved for compressing air (instead of

using pistons), hence the name. As the screws mesh towards each other, air is compressed and pushed

inside a storage tank.

Centrifugal Air Compressor

A centrifugal air compressor is also called a dynamic compressor. It is applicable when the demand for

compressed air is high. In this unit, a high-speed rotating impeller increases velocity of air, which is

directed towards a diffuser that converts the velocity of air into pressure. A centrifugal air compressor

requires more energy to operate than the other two air compressors.

While there are compressors that use rotating impellers to generate air pressure, positive-

displacement compressors are more common and include the models used by homeowners,

woodworkers, mechanics and contractors. Here, air pressure is increased by reducing the size of

the space that contains the air. Most of the compressors you'll run across do this job with areciprocating piston.

Like a small internal combustion engine, a conventional piston compressor has a crankshaft, a

connecting rod and piston, a cylinder and a valve head. The crankshaft is driven by either anelectric motor or a gas engine. While there are small models that are comprised of just the pump

and motor, most compressors have an air tank to hold a quantity of air within a preset pressurerange. The compressed air in the tank drives the air tools, and the motor cycles on and off to

automatically maintain pressure in the tank.

At the top of the cylinder, you'll find a valve head that holds the inlet and discharge valves. Both

are simply thin metal flaps

one mounted underneath and one mounted on top of the valve plate.As the piston moves down, a vacuum is created above it. This allows outside air at atmospheric

pressure to push open the inlet valve and fill the area above the piston. As the piston moves up,the air above it compresses, holds the inlet valve shut and pushes the discharge valve open. The

air moves from the discharge port to the tank. With each stroke, more air enters the tank and the

pressure rises.

Typical compressors come in 1- or 2-cylinder versions to suit the requirements of the tools they

power. On the homeowner/contractor level, most of the 2-cylinder models operate just like

single-cylinder versions, except that there are two strokes per revolution instead of one. Some

commercial 2-cylinder compressors are 2-stage compressorsone piston pumps air into a second

cylinder that further increases pressure.

Compressors use a pressure switch to stop the motor when tank pressure reaches a preset limitabout 125 psi for many single-stage models. Most of the time, though, you don't need that much

pressure. Therefore, the air line will include a regulator that you set to match the pressure

requirements of the tool you're using. A gauge before the regulator monitors tank pressure and agauge after the regulator monitors air-line pressure. In addition, the tank has a safety valve that

opens if the pressure switch malfunctions. The pressure switch may also incorporate an unloader

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valve that reduces tank pressure when the compressor is turned off.

Many articulated-piston compressors are oil lubricated. That is, they have an oil bath that splash-lubricates the bearings and cylinder walls as the crank rotates. The pistons have rings that help

keep the compressed air on top of the piston and keep the lubricating oil away from the air.

Rings, though, are not completely effective, so some oil will enter the compressed air in aerosolform.

Having oil in the air isn't necessarily a problem. Many air tools require oiling, and inline oilers

are often added to increase a uniform supply to the tool. On the down side, these models requireregular oil checks, periodic oil changes and they must be operated on a level surface. Most of all,

there are some tools and situations that require oilfree air. Spray painting with oil in the airstream

will cause finish problems. And many new woodworking air tools such as nailers and sanders are

designed to be oilfree so there's no chance of fouling wood surfaces with oil. While solutions tothe airborne oil problem include using an oil separator or filter in the air line, a better idea is to

use an oilfree compressor that uses permanently lubricated bearings in place of the oil bath.

A variation on the automotive-type piston compressor is a model that uses a one-piece

piston/connecting rod. Because there is no wrist pin, the piston leans from side to side as the

eccentric journal on the shaft moves it up and down. A seal around the piston maintains contact

with the cylinder walls and prevents air leakage.

Where air requirements are modest, a diaphragm compressor can be effective. In this design, a

membrane between the piston and the compression chamber seals off the air and preventsleakage.

Compressor powerOne of the factors used to designate compressor power is motor horsepower. However, this isn't

the best indicator. You really need to know the amount of air the compressor can deliver at aspecific pressure.

The rate at which a compressor can deliver a volume of air is noted in cubic feet per minute(cfm). Because atmospheric pressure plays a role in how fast air moves into the cylinder, cfmwill vary with atmospheric pressure. It also varies with the temperature and humidity of the air.

To set an even playing field, makers calculate standard cubic feet per minute (scfm) as cfm at sea

level with 68 degrees F air at 36% relative humidity. Scfm ratings are given at a specificpressure3.0 scfm at 90 psi, for example. If you reduce pressure, scfm goes up, and vice versa.

You also may run across a rating called displacement cfm. This figure is the product of cylinder

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displacement and motor rpm. In comparison with scfm, it provides an index of compressor pump

efficiency.

The cfm and psi ratings are important because they indicate the tools that a particular compressor

can drive. When choosing a compressor, make sure it can supply the amount of air and the

pressure that your tools need.