Air Inlet System, Functional Description - Sullair LS20 Operator's Manual And Parts List

proportionately with a rise of line pressure from 101
to 110 psig (7 to 7.6 bar).
MODULATING MODE WITH OPTIONAL SPIRAL
VALVE - 100 to 110 PSIG (6.9 TO 7.6 bar)
As air demand drops below the rated capacity of the
compressor, the line pressure will rise above 100
psig (6.9 bar). As a result, the differential pressure
regulator for the spiral valve gradually opens, apply-
ing air pressure to the spiral valve actuator. Air pres-
sure at the actuator expands the diaphragm. The
rack, in turn, engages with the pinion mounted on
the spiral valve shaft assembly. This results in a
rotary motion. As the spiral valve rotates, it starts
opening the bypass ports gradually. Excess air is
then being returned back internally to the suction
end of the compressor unit. Now the compressor is
fully compressing only that amount of air, which is
being used. As air demand keeps dropping further,
the spiral valve keeps opening more and more until
all the bypass ports are fully open. At this point, the
spiral valve has moved into the unload (minimum)
position.
The spiral valve provides a modulation range from
100 to 50%. During this period, the pressure rises
approximately from 100 to 105 psig (6.9 to 7.2 bar).
As the air pressure exceeds 105 psig (7.2 bar), the
differential pressure regulator controlling the inlet
poppet valve starts opening and forcing the poppet
closed, thus throttling inlet air flow to the compres-
sor. The inlet poppet valve provides a modulation
range from 50 to 40%. During this period, the pres-
sure rises approximately from 106 to 110 psig (7.3
to 7.6 bar). During this range, the spiral valve
remains in the unload position.
UNLOAD - IN EXCESS OF 110 PSIG (7.6 BAR)
LINE PRESSURE
When no air is being used,the service line pressure
rises to the setting (cut-out pressure) of the pres-
sure switch. the pressure switch opens, interrupting
the electrical power to the solenoid valve. At this
time, the solenoid valve allows dry sump tank air
pressure or service air pressure through a shuttle
valve to be applied directly to the inlet valve piston
and keep it closed. Simultaneously, the solenoid
valve sends a pneumatic signal to the blowdown
valve. The blowdown valve opens the sump to the
compressor intake reducing the sump pressure to
approximately 15 to 20 psig (1.0 to 1.4 bar). The
check valve in the air service line pressure prevents
line pressure from returning to the sump.
When the line pressure drops to the low setting
(cut-in pressure) of the pressure switch (usually 100
psig [6.9 bar]), the pressure switch closes, re-ener-
gizing the 3-way solenoid valve and allowing the
blowdown valve to close. The re-energized solenoid
valve again prevents pre sure from reaching the
inlet valve. The inlet valve is fully open and the com-
pressor delivers full rated capacity. Should the pres-
sure begin to rise, the pressure regulator will
resume its normal function as previously described.
To accommodate varied periods of time when there
are not any air requirements, "Dual-Control" is uti-
lized. This feature allows you to set the compressor
in an automatic position whereby the compressor
will shut down when no compressed air require-
ment is present and restart as compressed air is
needed.
2.8 AIR INLET SYSTEM, FUNCTIONAL DESCRIP-
TION
Refer to Figure 2-6. The Compressor Inlet System
consists of a dry-type air filter and an air inlet
valve.
The poppet-type modulating air inlet valve directly
controls the amount of air intake to the compressor
in response to the operation of the pressure regula-
tor (see Modulating Mode, Section 2.6 [Supervisor
Controller] or Section 2.7
The inlet valve also acts as a check valve, thus pre-
venting reverse rotation when the compressor is
shut down.
"The Plastic Pipe Institute recommends against
the use of thermoplastic pipe to transport com-
pressed air or other compressed gases in
exposed above ground locations, e.g. in exposed
Figure 2-6 Air Inlet System
Section 2
DESCRIPTION
[Electro-Mechanical]).
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