Sullair LS20T Operator's Manual And Parts List page 15

control pressure regulator valve modulates the inlet
poppet valve.
UNLOAD MODE - EXCESS OF 535 PSIG (36.8
BAR)
As the required air is reduce, the discharge pres-
sure and line pressure rise above the 535 psig (36.8
bar), the Supervisor Controller activates the unload
solenoid valve which in turn pressurizes the blow-
down valve. This opens the blowdown valve, which
allows discharge air to flow back to the compressor
inlet. Since the inlet poppet valve is fully closed, the
air pressure from the sump tank will be relieved
through the blowdown valve, which will reduce the
sump pressure. Some of the outgoing air will flow
directly into the compressor inlet to avoid cavitation
during this time of blowdown. As the sump pres-
sure drops, motor power consumption is also
reduced. The unload pressure regulator is set to
maintain the unload pressure at the designated
value, 170 psig (11.7 bar). At this time, the com-
pressor is in the unload mode.
When the line pressure drops back to the load point
(cut-in pressure) of the pressure transducer, usual-
ly 525 psig (36.1 bar), the compressor will change
state back to the modulating mode as discussed
earlier. This cycle will repeat itself, maintaining the
demand required on the system line supply.
SHUTDOWN MODE
When the compressor is shut down based on a
manual shutdown, a safety shutdown or an auto-
matic shutdown from the Supervisor Controller
touch pad, the unload solenoid valve is energized
allowing air to flow through the check valve and into
the poppet valve keeping the inlet poppet valve
closed. This also opens the blowdown valve to
allow compressed air to vent back above inlet pop-
pet valve through the inlet filter. The control lines
are properly sized and routed to allow the com-
pressed air to relieve to atmosphere rather than
below the inlet poppet valve.
If the compressor Supervisor Controller is in the
automatic mode, the compressor will shut down
after running unloaded for a specific amount of
time. The reverse also holds true, if the system line
pressure requires additional compressed air, the
compressor will start automatically to satisfy this
demand.
Section 2
DESCRIPTION
9