| It is the fourth utility. Compressed
air, along with gas, electricity and water, is essential to most
modern industrial and commercial operations. It runs tools and
machinery, provides power for material handling systems, and
ensures clean, breathable air in contaminated environments. It
is used by virtually every industrial segment from aircraft and
automobiles to dairies, fish farming, and textiles.
| A plant's expense for its compressed
air is often thought of only in terms of the cost of the
equipment. Energy costs, however, represent as much as 70% of
the total expense in producing compressed air. As electricity
rates escalate across the nation and the cost of maintenance and
repair increases, selecting the most efficient and reliable
compressor becomes critical.
|Rotary Screw Compressor: The Plant
| Rotary screw compressors operate on
the principle of positive displacement. Filtered air enters the
inlet of the airend where male and female rotors unmesh. The air
is trapped between the rotors and the airend housing. This space
is reduced as the rotors remesh on the opposite side of the
airend. Thus, the air is compressed and moved to the discharge
| Oil injected into the housing mixes
with the air to seal, lubricate, and remove the heat generated
by compression. This oil forms a thin film between the rotors
that virtually eliminates metal-to-metal contact and wear. The
oil is separated from the compressed air, cooled, filtered, and
returned to the injection point. The compressed air then passes
through an aftercooler to reduce its temperature and is ready
for the air treatment equipment.
1. Dynamic Centrifugal/Axial -
Use a rotating impeller to impart velocity to the air,
which is converted to pressure.
Rotary - Compress air
through the action of rotating elements. Most common types
are rotary screw, which uses rotating male and female rotors
to compress air, and sliding vane, which uses radially
Reciprocating - Compress
air through the use of a reciprocating piston.
| Select air
compressors based on your plant needs. Positive displacement
compressors take in quantities of air and mechanically reduce
the space occupied by the air to increase pressure. Dynamic
compressors use the mechanical action of rotating impellers to
transfer pressure to the air.
a Compressed Air System / Selecting
an Air Compressor / Maintenance
/ Glossary and