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CHAPTER 1.
DEFINITIONS AND RESPONSIBILITIES
Section 1.
AIR COMPRESSOR PLANT
1 COMPONENTS OF AN AIR COMPRESSOR PLANT.  Compressed air is a form of power
that has many important uses in industrial activities. Air compressor plants
are used to provide an adequate quantity of compressed air at sufficient
pressure to various points of application. Distribution of compressed air is
found in NAVFAC MO-209, Maintenance of Steam, Hot Water, and Compressed Air
Distribution Systems.
Components of a plant are:  air compressor, intercool-
ers, aftercoolers, moisture separator, air receiver, and controls (figure l-l).
2 AIR COMPRESSOR.  The air compressor is the heart of a compressed air
plant.  Compressors are used to increase the pressure of air from the initial
conditions (air intake) to the discharge conditions (air discharge).
Compressors may be used as vacuum pumps. A vacuum pump has an intake that is
below atmospheric pressure and usually compresses to no higher than
atmospheric pressure.  The degree of vacuum attainable is dependent upon the
type of system, leakage into the system, and limitations of the equipment.
The main types of air compressors are positive displacement and dynamic.
2.1 Positive Displacement Compressors. There are two basic types of positive
displacement compressors.
In one, air is compressed as the volume of the
enclosed space is reduced. In the other, a definite quantity of air is
trapped and transferred from the suction intake to the discharge port without
reducing its volume.  Pressure increase is caused by backflow into the casing
when the discharge port is uncovered. Examples of the first type are
reciprocating compressors,  rotary sliding vane compressors, and rotary liquid
piston compressors.
An example of the second type is the rotary twin-lobe
compressor.  Refer to chapter 2 for details.
2.2 Dynamic Compressors.  Dynamic compressors operate by imparting velocity
and pressure to the admitted air, through the action of a rapidly spinning
impeller or rotating vanes. The main types of dynamic compressors are
centrifugal and axial compressors. Refer to chapter 3 for details.
2.3 Maximum Pressures and Capacities of Air Compressors. The approximate
maximum pressures in pounds-force per square inch gauge (psig), and the
approximate maximum capacities in cubic feet per minute (cfm) for various
types of compressors are given in table l-l.
3 AUXILIARY EQUIPMENT.  The 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. Refer to chapter 4, section 1 for details.
3.2 Silencers. Silencers reduce objectionable compressor suction noise.
Refer to chapter 4, section 2.
3.3 Intercoolers and Aftercoolers. Intercoolers are used between consecutive
stages of multistage compressors to remove the heat of compression.
Aftercoolers are installed on the compressor discharge lines to remove the
heat of compression after compression is completed. Both are effective in
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