Compressed air is used in many operations and processes and as a source of energy for heating, ventilating, and air conditioning (HVAC) and process actuators and motors. It may also be supplied for low pressure systems and used for pneumatic control. Air can be compressed in several different ways and supplied at varying pressures and degrees of filtration depending on its use.
A typical compressed air system is capable of producing instrument quality air for pneumatic HVAC controls, tools, conveying systems, and general plant air. The system
consists of a single motor driven single stage rotary screw compressor
with inlet air filter, a safety relief valve, aftercooler, air/oil
separator, air receiver with safety relief valve, prefilter, air dryer,
afterfilter, oil/water traps, and oil/water separator.
are most often supplied skid mounted as a packaged unit.Theassembled
package includes all major components, controls, and a sound attenuation
enclosure. The unit only requires mounting to a foundation,hook up to system piping, connection to the oil water separator, and power connection.
are various types of compressors: Rotary helical screw air compressors
are positive displacement machines. Atwin-screw compressor consists of
accurately matched rotors [one lobe (male) and one helix (female)] that
mesh closely when rotating within a close tolerance common housing. One
rotor is motor driven while the other is gear driven, turning it in a
The rotors uncover inlet posts at one
end allowing air to flow in. As the rotors continue to rotate the air is
compressed by the minishing volume between the rotors . At the end of
the rotors, ports allow the now compressed air to exit. One or more
stages may be used.
These compressors are used in systems
up to 3000 cubic feet per minute (cfm). They are usually oil injected
to increase sealing, lubricate rotors, and provide cooling. They can
also be oil free. One or two stages can be used. They have
a low initial cost, no pulsation, are almost free of vibration, and do not require special foundations.
compressors compress air as it enters the center of a fluted casting,
housing a rotating impeller. The impeller imparts kinetic energy to the
gas which turns into potential energy as the gas velocity slows, thus
increasing pressure. Compression is a continuous process. One or more
stages may be used.
Centrifugal compressors are used in large systems
up to 15,000 cfm. A blow-off silencer is needed to control noise.
Centrifugal compressors require no ubrication in contact with the air
stream and therefore provide oil free air.
positive displacement compressors use a piston in a cylinder to compress
air up to a capacity of 6,000 cfm . Air enters the cylinder through a
valve when the piston is going down. The valve closes when the piston
starts to go up. As the piston approaches the top ofthe cylinder, the
air is compressed by the decreasing volume. An exhaust valve opens when
the piston is near the top of the cylinder allowing the compressed air
to exit. The cycle is them repeated.
Rotary sliding vane
compressors use a rotor eccentrically mounted in a cylinder. The rotor
has eight or more slots cut along its length .Vanes are placed in the
slots. As the rotor rotates, the vanes move out from centrifugal force.
As the rotor continues through a rotation, the rotor housing causes the
vanes to move back in the slot ofthe rotor.
The volume of air
between the housing, eccentrically mounted rotor, and two vanes changes
as the rotor rotates, compressing the air. read more