Sullair LS-25 Operator's Manual And Parts List page 26

Section 2
DESCRIPTION
Figure 2-7 Air Inlet System
pressure range would operate in the same manner
except at stated pressures.
START MODE - 0 TO 50 PSIG (0 TO 3.4 BAR)
When the compressor START button is depressed,
the pressure will quickly rise from 0 to 50 psig (0 to
3.4 bar). During this period, the spiral valve is fully
closed and the inlet butterfly valve fully open. As a
result, the compressor runs at full capacity.
FULL LOAD MODE - 50 TO 100 PSI (3.4 TO 6.9
BAR)
When the compressed air rises above 50 psi (3.4
bar), the minimum pressure valve opens allowing
compressed air to flow into the service line. Both
the spiral valve as well as the inlet butterfly valve re-
main in the full load position as long as the com-
pressor is running at 100 psi (7.6 bar) or below.
MODULATION MODE - 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 pres-
sure regulator for the spiral valve gradually opens
applying air pressure to the spiral valve actuator. Air
pressure at the actuator diaphragm causes a rack,
which is engaged on a pinion, to move linearly. The
movement of the rack imparts a rotary motion to the
pinion which is attached to the spiral valve, which in
turn rotates. As the spiral valve rotates, it starts
opening the bypass ports gradually. Excess air is
then being returned back to suction. Now the com-
20
pressor is 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
position.
The spiral valve provides a modulation range from
100 to 50% capacity. During this period, the pres-
sure rises approximately from 100 to 108 psig (6.9
to 7.4 bar). As the air pressure exceeds 108 psig
(7.4 bar), the differential pressure regulator con-
trolling the Sullicon Control opens. This allows the
air pressure to the diaphragm chamber of the
Sullicon Control, which starts partially closing the
inlet butterfly valve. The inlet butterfly valve pro-
vides modulation range from 50 to 40% capacity.
During this period, the pressure rises approximate-
ly from 108 to 110 psig (8.5 to 8.6 bar). During this
range, the spiral valve remains in the unload posi-
tion.
UNLOAD MODE - IN EXCESS OF 110 PSIG (7.6
BAR)
When a relatively small amount, or no air is being
used, the service line pressure keeps on rising.
When it exceeds 110 psig (7.6 bar), the air pressure
switch opens, or Supervisor "load" contacts open,
de-energizing the pilot valve. The line pressure
through the pilot valve closes the inlet butterfly,
opens the spiral valve, and at the same time opens
the blowdown valve. Reduced sump pressure dur-