4500P-7500 USER MANUAL SECTION
22
psig (3.4 bar) the minimum pressure valve opens
allowing compressed air to flow into to the service
line. From this point on the WS Controller monitors
the line pressure which controls the VSD. The
pressure regulator and solenoid valves remain
closed with the inlet valve fully open, running at 100
psig (6.9 bar) or lower.
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 2-5) 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 de-
energizes the solenoid valve allowing receiver 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 receiver
tank pressure. The check valve in the air service line
prevents line pressure from back-flowing to the
receiver 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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