COMPRESSED AIR PLANTS
1. COMPONENTS OF AN AIR COMPRESSOR PLANT. Air compressor plants are used to
provide an adequate quantity of compressed air at sufficient pressure to the
v a r i o u s points of application. The main components of an air compressor plant
are the air compressor, the auxiliary equipment, and the controls. NAVFAC
MO-206 provides detailed operation and maintenance procedures of compressed
a i r plants.
2. AIR COMPRESSOR. The air compressor is the heart of a compressed air
p l a n t . Compressors are used to increase the pressure of the air from Initial
c o n d i t i o n s (air intake) to the discharge conditions (air discharge).
Compressors may be used as vacuum pumps as well. A vacuum pump has an intake
that is below atmospheric pressure and usually compresses to no higher than
atmospheric pressure. The main type of air compressors are positive
displacement and dynamic. The manufacturer's technical manual should provide
detailed operating and maintenance of the compressor.
2.1 Positive Displacement Compressors. There are two basic types of positive
displacement compressors. In one, the air is compressed as the volume of the
enclosed space is reduced. I n the other, a definite quantity of air is
trapped and transferred from the suction intake to the discharge port without
reducing its volume. The pressure increase is caused by backflow into the
casing when the discharge port is uncovered. Example of the first type are
the reciprocating compressors, rotary sliding vane compressors, and rotary
liquid piston compressors. An example of the second type is the rotary
2.2 Dynamic Compressors. Dynamic compressors operate by imparting velocity
a n d pressure to the admitted air, through the action of a rapidly spinning
i m p e l l e r or rotating vanes. The main types of dynamic compressors are the
centrifugal and the axial compressors.
3. AUXILIARY EQUIPMENT. T h e following auxiliary equipment is required for
the proper operation of an air compressor plant.
3 . 1 Air Intake Filters. Filters prevent the admission of atmospheric dust to
the air compressor.
3 . 2 Silencers. Silencers reduce objectionable compressor suction noise.
3 . 3 Intercoolers and Aftercoolers. Intercoolers are used between consecutive
stages of compression to remove the heat of compression. A f t e r c o o l e r s are
installed on the compressor's discharge lines to remove the heat of
compression after compression is completed. They are effective in removing
moisture and oil from the compressed air as well.
3.4 Separators. Separators remove and collect the entrained water and oil
p r e c i p i t a t e d from the air.
3.5 Traps. Traps drain condensed moisture and oil from separators,
i n t e r c o o l e r s , aftercoolers, receivers, and distribution piping.