Figure 8-5.—Typical screw
and to cool the air during the compression cycle. Oil is
removed from the compressed air by an oil separator
before it leaves the service valves.
SCREW TYPE OF COMPRESSOR
The screw type of air compressor is an oil-injected,
helical screw, direct drive, positive displacement air
compressor. It maybe single or dual stage (fig. 8-5). The
design is relatively simple, being a pair of precisely
matched spiral-grooved rotors (fig. 8-6) turning within
a single-piece twin-bore cylinder. The rotors provide
positive-displacement-internal
compression-smoothly,
without surging. The matched rotors, one lobed and one
grooved, intermesh in the twin bores of the single-piece
cylinder. As the rotors turn and unmesh at one end, air
is taken in, compressed, and moved through the
twin-bore cylinder by the rotors as they rotate. Figure
8-7 shows the steps of airflow past the rotors; figure 8-8
shows aside view of the airflow through the compressor.
Compression takes place within the twin-bore cylinder
Figure 8-6.—Male and female screw type of air compressor
rotors (matched set).
type of air compressor.
Figure 8-7.—The compression cycle of a screw type of air
compressor.
8-4
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