Sullair LS-200S Operator's Manual And Parts List page 54

Section 9
VARIABLE SPEED DRIVE APPLICATIONS
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.
While at minimum speed, if the system pressure
reaches 106 psig (7.3 bar), or alternatively set
unload pressure, the compressor 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
48
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.
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.