Vsd Control Operation; Description Of Components; Control System, Functional Description; Start Mode- 0 To 50 Psig (0 To 3.5 Bar) - Sullair 3007 Operators Manual & Parts Lists

7.1 DESCRIPTION OF COMPONENTS

The variable speed drive unit is located in the machine
electrical enclosure. The heat sink for the drive extends
through the back of the enclosure, and is cooled by airflow
through the compressor enclosure.
7.2 CONTROL SYSTEM,
FUNCTIONAL DESCRIPTION
Refer to Figure 2-5. The purpose of the compressor control
system is to regulate the amount of the air being
compressed to match the amount of compressed air being
used. The Capacity Control System consist of variable
speed drive, solenoid valve, regulating valve, and the inlet
valve. The functional description of the control system is
described below in six distinct phases of operation. The
following description text applies to 3000V, 3000PV,
3700V and 4500V series variable speed drive
compressors with WS Controller. Depending on the
model, the compressor can be operated at a setpoint
pressure from 60 to 175 psig (4.1 to 12.1 bar). Refer to the
nameplate for operating pressure range. The WS
Controller will automatically set the frequency range based
on the selected pressure. For explanatory purposes, this
description will apply to a compressor with an operating
pressure of 100 psig (6.9 bar), and load delta setting of 6
psi (0.4 bar). The load delta has a default setting of 10 psi
(0.7 bar), but is recommended to set at 6 psi (0.4 bar) for
most efficient operation. A compressor with any other
pressure range would operate in the same manner except
stated pressures.

Start Mode- 0 to 50 PSIG (0 to 3.5 Bar)

When the WS Controller "
depressed, the VSD ramps the motor to full speed and the
receiver tank pressure will quickly rise from 0 to 50 psig
( 0-3.4 bar). During this period, both the regulator and
solenoid valves are closed, the inlet valve is fully open and
the air-end delivers full capacity to the receiver tank. The
rising compressor air pressure is isolated from the service
line in this phase by the minimum pressure valve set at
approximately 50 psig (3.4 bar).
SULL AIR
® ®
SULL AIR
®
Section 7
VSD CONTROL
OPERATION
" (START) button is
3000-4500 Operator's Manual and Parts List
®
Full Load Mode- 50 to 100
PSIG (3.4 to 6.9 Bar)
When the compressed air pressure rises over 50 psig
(3.4 bar) the minimum pressure valve opens allowing
compressed air to flow into the service line. From this point
on the line pressure is continually monitored by the WS
Controller, which controls the variable speed drive. The
pressure regulator and solenoid valve remain closed with
the inlet valve fully open running at 100 psig (6.9 bar) or
below.

Variable Speed Drive Part Load Control

If less than rated capacity of compressed air is being used,
the service line pressure will rise above 100 psig
(6.9 bar). Consequently, the Variable Speed Drive will
begin to decelerate the motor, thereby reducing the output
capacity to match demand. The drive will continuously
adjust the motor speed (accelerate or decelerate) to
maintain a line pressure of 100 psig (6.9 bar). In this mode
the VSD will operate within the appropriate frequency
range determined by the WS Controller.
Modulating Mode- 100 to 106
PSIG (7.3 to 6.9 Bar)
During low demand periods and with the Variable Speed
Drive 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 7-7)
gradually opens, directing air pressure to the inlet control
valve piston. This action causes the inlet valve to partially
close, thereby reducing the air entering the compressor
until it matches the amount of air being used. The control
system functions continually in this manner between the
limits of > 101 psig (7.0 bar) to 106 psig (7.3 bar), in
response to varying flow 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 any accumulated moisture
from the control line. When the discharge pressure rises
above 106 psig (7.3 bar), or alternatively set unload
pressure the compressor unloads.
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