Compressors come in a variety of styles, the differences lying in the power sources they use, their method of operation and their size. Industrial air compressors are available in three main configurations: reciprocating compressors, rotary screw compressors and centrifugal compressors. Reciprocating air compressors create air compression with pistons; these have a broad range of output capabilities and are fairly cost-effective. Rotary screw compressors are generally configured as regular, lubricated compressors, which may be designed as oilless air compressors, while centrifugal air compressors are always oil-free. Rotary screw and reciprocating compressors may be designed as portable air compressors or as central facility units. The oil-free compressor style is being adopted by another common design, the rotary air compressor. This air compressor comes in a variety of sizes, including the mini air compressor, which can be as small as ten pounds. Regardless of the type of air compressor a buyer is shopping for, they can buy it new or pay a slimmer price and get a used air compressor that is often in excellent shape and will last long enough to be worthwhile. Air compressors vary in size as well as the ways in which they are powered; they can be powered by electricity or a gas motor. Electric air compressors come equipped with a power cord, while 12 volt batteries, which are always a part of 12 volt air compressors, can be recharged in an electrical outlet or a car cigarette lighter, depending on the size. Gas air compressors operate by way of a gasoline run motor.
Automotive industries use air compressors extensively for tire inflation, parts cleaning and surface finishing; homes and commercial businesses use air compressors in a range of appliance and recreational product applications such as paintball gun canisters. Gas stations use compressors for gas pumps; airbrush paint applications also use air compressors in auto body shops, commercial and private airbrush art and home painting projects. Power tools such as jackhammers, jacklegs, needle scalers, tuggers/winches, air chisels, chipping hammers and rock drills use compressors or portable air compressors. Sandblasters also operate on compressed air. Other tools that use compressed air include nail guns, sanders, drills, staplers and spray guns. Industrial air compressors provide air for air purification systems, air lock systems, blast forges and temperature control systems. Another use for air compressors is filling the metal oxygen cylinders used by deep sea divers to swim and research. Air compressors are usually made from one of three basic metals: aluminum, steel and cast iron. However, when lightweight compressors are needed, such as a mini compressor or portable compressor, plastic is used in place of metal.
Air compressors are mechanical devices that compress air by pulling it in from the atmosphere and decreasing its volume while simultaneously increasing its pressure. Reciprocating air compressors use pistons to do this work, which move in and out of a cylindrical mouth piece that lets the air go in and out without altering the compression process and only releasing the air when it will be useful. Rotary screw compressors use two helical screws fitted into one another, rotating quickly in opposite directions, which pulls the air in small doses, compressing it while it cycles through the rotating screws. Both of these use oil to lubricate internal parts, and oil separators are often attached downstream to filter out contaminating lubricants, although some rotary screw compressors are oil-free. Using oilless air compressors is ideal for applications where a pure air stream is required, as downstream filter cleaning can add to maintenance costs and is not guaranteed to capture every drop of oil. Centrifugal air compressors are dynamic compressors that use a rotating impeller to create air velocity, which is pushed through a diffuser and converted into pressure. The compressed air is then stored in a holding tank or released into a pressure system, ready for work.
Compressors have two components: a compressing mechanism and a power source for the compressing mechanism. The energy for compression can be taken from a gas-powered motor, an electrical motor or a power takeoff. The various compressing mechanisms that do the actual work of compression are pistons, vanes and impellers. By storing and compressing the air, air compressors convert mechanical energy into pneumatic energy. Air compressor manufacturers often design products that can be driven by natural gas, which greatly reduces cost and energy consumption. Until recently, air compressors have mainly been used for surface finishing, cleaning and inflating applications - its use as a power generator has not been seriously explored until now. As automotive manufacturers search for alternatives to internal combustion engines, many manufacturers are beginning to experiment with the clean pneumatic power provided by air compressors. Because of air compressors' importance to an extensive variety of industrial operations, their widespread use will continue into the foreseeable future.
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Air Compressor Types
- 12 volt air compressors are machines that require 12 volts of power
to reduce the volume of air in a tank in order to increase the
pressure.
-
have flow in the axial direction by accelerating air tangentially with
blades attached to the rotors. This increases the kinetic energy of
the air and diffuses it through static vanes to increase its pressure.
-
act on air with blades on a rotating impeller. The rotary motion of
the air causes an outward velocity from the centrifugal force, and then
a diffuser transforms this outward velocity into pressure.
- are mechanisms used for compressing
air to higher than atmospheric levels.
-
achieve compression with the use of a flexing diaphragm that moves back
and forth in a closed chamber; the design is an alteration of the reciprocating
piston concept. The motion of the connecting rod under the diaphragm
causes the flexing and only a short stroke is needed to generate similar
pressure effects as those of a reciprocating piston compressor.
-
use both sides of the piston to compress the air, both the forward and
the back stroke.
-
use a high-pressure jet stream. The drive of the stream is transferred
to the low pressure of the air.
- Electric air compressors are machines that use electrical power to pressurize air before releasing it in a high energy form.
-
have an adjustable compression piston that moves along the length of
a steel cylinder column. The guiding and compression pistons collide
at the return stroke because the compressed air pushes back the compression
piston in the last stage.
- Gas air compressors are gas-fueled machines that reduce the volume of air in order to use
the pressurized air for power.
- are
mechanical devices used for industrial purposes that provide air at
higher than
atmospheric pressure.
-
are oil-free and work without piston rings. A series of labyrinths creates
the seal between the cylinder wall and the piston.
-
have only one moving part, the impeller shaft assembly. The service
liquid rotating in its casing forms the liquid ring seal, and air enters
through the suction port, moves between the impeller blades and is compressed
before discharging.
-
use two mating lobes on different shafts that rotate in opposite directions
to capture incoming air and compress it against the casing. Lobe compressors
supply very high flows at pressure ranges between non-positive displacement
compressors and other types of positive displacement units.
- Mini air compressors are machines that reduce the volume of air in order to pressurize it and
convert mechanical energy into pneumatic power. The pressurized air can
then be used for a variety of applications; due to the limited size of
mini air compressors, however, the output is small and limited to 250
pounds per square inch (PSI).
- depend on motion to transfer energy from the compressor
rotor to the air. Initial acceleration of the air produces a negative
(suction) pressure at the inlet port, which draws air in.
- Oilless air compressors provide air and power for various tools, machinery and manufacturing processes in industries that require clean air.
- Portable air compressors are hand-held systems that do
not require an electrical outlet.
- work by successively trapping a volume of air and
reducing it, thereby increasing the pressure. The quantity of heat produced
rises proportionally to the pressure rise, resulting in substantial
temperature increases of the air and the compressor itself.
-
move a piston to the top of a cylinder to create compression. These
require either water or air cooled.
- reduce the volume of air by compressing it between
intermeshing, counter-rotating components that force the air into a
tank.
- Screw compressors
use two contra-rotating rotors that turn in a synchronous mesh. As air
enters the sealed chamber, the rotors revolve, reducing the volume of
trapped air and sending it compressed through the discharge port at
the designated pressure level.
-
move pistons parallel to the crankshaft, either by a cam or by a plate
mounted axially on the shaft and inclined to it.
- Used air compressors are previously owned machines that reduce the volume of air in order to increase its pressure.
-
have an eccentrically mounted rotor that is the only moving part and
rotates within the stator. As the rotor rotates, centrifugal force forces
the vanes from their slots, forming compression cells, and this pumping
action of the vanes sliding in and out moves the air from the inlet
side of the compressor to the outlet side.
Air Compressor Terms
-
The removal of heat when the compression process is complete.
- A component
of an air compressor that allows the user to adjust the air pressure in
the air line.
- A condition caused
by a difference in pressure in which air will flow back into the distribution
pipes rather than in the intended direction.
- The element that houses
the rotor and related internal components of an air compressor. This includes
the integral inlet and discharge connections.
- The lowest
amount of differential pressure something is able to withstand without
deformation.
-
The ratio of the absolute inlet pressure to the absolute outlet pressure.
Compression/pressure ratio typically applies to a single stage of compression
but could also apply to a full multistage compressor.
- The piston compartment
in an actuator or reciprocating compressor.
- The piping
between the aftercooler and the compressor and the air receiver and the
cooler separator.
- A flange-mounted belt
drive, motor or direct coupling between the engine or motor and the compressor.
- The operation of
an air compressor at full speed, having a completely open inlet and discharge
delivering upper limit airflow.
- An adjustable fixed
part that directs the flow of air approaching the inlet of an impeller.
- The component of
the rotating element of a dynamic compressor that gives energy to the
flowing medium through centrifugal force. An impeller is comprised of
blades that rotate with the shaft.
- A valve
intended to stop air pressure and volume from slipping out of the compressor
tank back into compressor heads when the compressor is not running.
- Heat Exchangers that eliminate heat produced during compression between
the stages of a compressor.
- The ratio of the
maximum rated compressor load to the average compressor load within a
certain period.
- A method
of control that permits the compressor to run either at no load or at
complete load at the same time that the driver remains at a constant speed.
Load/unload control is an attempt to match air delivery to the demand.
- The
highest-pressure level recommended for a compressor.
- When an air compressor
is running at full RPM and is wide open, but no air is sent because the
inlet is either closed off or modified and will not allow inlet air to
be trapped.
-
Compressor cylinders on a reciprocating compressor that run at low compression
ratios and undergo little temperature change. These are used mainly in
oil and gas field applications.
- The total pressure
(static plus velocity) at the inlet flange of the compressor.
- The difference
between the intake pressure and the discharge pressure
- The reversal
of flow in a dynamic compressor. Pumping/surge takes place when the handled
capacity is reduced to an insufficient pressure in order to maintain flow.
- A revolving element
of a compressor. It consists of the impeller and shaft and may have shaft
sleeves and a thrust balancing device.
- The part that the rotating
elements are attached to and through which energy is transferred from
the prime mover.
- Mechanisms used
to position the impeller or to shield the shaft.
- The pad the compressor
is mounted on. This is implanted in concrete and usually metallic.
- The interaction between
the stages of a centrifugal compressor. In the design of a multi-stage
compressor, every stage can only run at one point of its characteristic
curve, and the determination of this point is done through the design
conditions of temperature, flow and pressure.
- The capacity in
a dynamic compressor under which the process becomes unsteady.
- Part
of a revolving element that offsets the thrust of compressor impellers.
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