Sullair LS20 Operator's Manual And Parts List page 17

Figure 2-5B Control System with Electro-Mechanical Controller
and thereby reducing the latter's air delivery. The air
throttling of the inlet poppet valve system increases
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
DESCRIPTION
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.
Section 2
11