SECTION 2 3000P-4500 USER MANUAL
21
VSD PART LOAD CONTROL
The service line pressure increases to a value above
100 psig (6.9) if the demand is less than the
compressor's rated capacity. In this condition, the
VSD slows the motor's rpm which reduces the output
to match the demand. The drive continuously adjusts
the motor's rpm to maintain a 100 psig (6.9 bar) line
pressure.The WS Controller maintains the correct
frequency when the VSD is operating in this mode.
MODULATING MODE-100 TO 106 PSIG
(7.3 TO 6.9 BAR)
During low demand periods and with the VSD
running at minimum speed, the line pressure can
continue to rise. When the line pressure reaches
101-102 psig (approximately 7 bar), the regulator
valve (Figure 2-4) gradually opens, directing air
pressure to the inlet control valve piston. This action
causes the inlet valve to partially close, thereby
reducing the air flow entering the compressor until it
matches the demand. The control system functions
continuously in this manner between less than 101
psig (7.0 bar) to 106 psig (7.3 bar), in response to
varying system demand. The pressure regulator has
an orifice which vents a small amount of air to the
atmosphere when the pressure regulator controls the
inlet valve. The orifice also bleeds off any
accumulated moisture from the control line. When
the discharge pressure rises above 106 psig (7.3
bar), or to a preset unload pressure, the compressor
unloads.
UNLOAD MODE-IN EXCESS OF 106 PSIG
(7.3 BAR)
When there is no demand or it is at a minimal level,
the service line pressure continues to rise. When it
exceeds 106 psig (7.3 bar), or reaches a preset
unload pressure value, the WS control system
deenergizes the solenoid valve allowing separator/
sump tank air pressure to be supplied directly which
closes the inlet valve. The solenoid valve
simultaneously sends a pneumatic signal to the blow
down valve which opens to the atmosphere, and
reduces the separator/sump tank pressure. The
check valve in the air service line prevents line
1800·2200 USER MANUAL pressure from back-
flowing to the separator/sump tank. The compressor
will shut down after the programmed unload time
setting expires (the default setting is zero [0] minutes
for an immediate shutdown upon unload). When the
line pressure drops to the low pressure setting of 100
psig (6.9 bar) the WS Controller starts the motor and
energizes the solenoid valve which closes the
blowdown valve. The re-energized solenoid valve
prevents line pressure from reaching the inlet control
valve, thereby allowing it to fully open, and the
compressor supplies compressed air to the system.
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