1800-3000 USER MANUAL SECTION 2
20
2.10 VSD CONTROL SYSTEM —
FUNCTIONAL DESCRIPTION
Refer to Figure 2-4. The controls consist of:
• a VSD
• a solenoid valve
• a regulating valve
• and an inlet valve.
Depending on the model, a compressor can be
operated at a setpoint pressure from 60 to 175 psig
(4.1 to 12.1 bar). The WS Controller automatically
sets the frequency range based on the selected
pressure. (The compressor’s operating range is on
its nameplate.)
The following paragraphs apply to a compressor with
a 100 psig (6.9) operating pressure and a 6 psi (0.4
bar) load delta setting.
Compressors with different pressure operating
ranges perform in the same manner.
START MODE - 0 TO 50 PSIG (0 TO 3.5 BAR)
Pressing the WS Controller START button (1) signals
the VSD to accelerate the motor to full speed,
causing the separator/sump tank pressure to rise
from 0 to 50 psig (0 to 3.4 bar). At this time both the
pressure regulator and solenoid valves are closed;
the inlet valve is fully open and the air-end provides a
full flow to the separator/sump tank. A minimum
pressure valve set at approximately 50 psig (3.4 bar)
isolates the rising compressor air pressure from the
service line.
FULL LOAD MODE - 50 TO 100 PSIG (3.4 TO
6.9 BAR)
When the compressed air pressure rises above 50
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 2-4)
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 de-
energizes 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
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.
NOTE
The load delta default setting is 10 psi (0.7
bar). Sullair recommends a setting of 6
psi (0.4) for the most efficient operation.
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