Sullair LS-200 Operator's Manual And Parts List page 70

Section 10
VARIABLE SPEED DRIVE
pressure the compressor unloads.
MODULATING MODE WITH OPTIONAL SPIRAL
VALVE:
This option does not have inlet modulation.
As demand decreases, the variable speed drive
reduces motor speed to maintain the set point pres-
sure. When the speed approaches the minimum
setting, a solenoid valve opens feeding air pressure
to the spiral valve actuator. This in turn expands the
diaphragm and engages the pinion mounted on the
spiral valve shaft assembly, resulting in a rotary
motion and full opening of the spiral valve, effec-
tively reducing the rotor length by 50%. Excess air
will be returned back internally to the suction side of
the compressor unit. In this mode, the VSD will
modulate the motor speed within a specified range
to maintain the set point pressure as follows:
Increasing demand condition:
If demand increases, the VSD increases the motor
speed until the set point pressure is achieved. If set
point pressure is not achieved while at maximum
speed, the controller will close the spiral valve,
thereby eliminating
Consequently, the VSD will regulate the motor
speed to achieve the set point pressure.
Decreasing demand condition:
While the spiral valve is open, if demand continues
to decrease the VSD will reduce the motor speed
until the set point pressure is achieved. This action
will continue until the minimum speed is reached.
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internal air bypass.
When the system pressure reaches 106 psig (7.3
bar), or alternatively set unload pressure, the com-
pressor unloads, or turns off.
UNLOAD MODE- IN EXCESS OF 106 PSIG (7.3
BAR)
When a relatively small amount or no air is being
used, the service line pressure continues to rise.
When it exceeds 106 psig (7.3 bar), or alternative-
ly set unload pressure, the Supervisor control sys-
tem de-energizes the solenoid valve allowing sump
air pressure to be supplied directly to close the inlet
valve. Simultaneously, the solenoid valve sends a
pneumatic signal to the blow down valve. The blow-
down valve opens to the atmosphere, reducing the
sump pressure. The check valve in the air service
line prevents line pressure from returning to the
sump. The compressor will shut down after the
unload time setting expires if programmed (the
default setting is zero [0] seconds for an immediate
shutdown upon unload).
When the line pressure drops to the low setting
pressure of 100 psig (6.9 bar) The Supervisor
Controller starts the motor and energizes the sole-
noid valve which closes the blow down valve. The
re-energized solenoid valve prevents line pressure
from reaching the inlet control valve, thereby allow-
ing it to fully open.
AUTOMATIC OPERATION
For VSD applications, the Supervisor Controller
should be set in the "Automatic" mode. This mode
allows the compressor to shutdown when no com-
pressed air requirement is present and restarts
when compressed air is needed.