3000PB, 3700B, 4500B, 3000PVB, 3700VB, 4500VB User Manual 2: Description
02250216-786 R01
Subject to EAR, ECCN EAR99 and related export control restrictions. 15
2.6 Control system, functional
description
Refer to Figure 2-5. The purpose of the compressor con-
trol system is to regulate
the amount of air being com-
pressed to match the amount of compressed air being
used. The cap
acity control system consists of a solenoid
valve, regulator valve and an inlet valve. The functional
description of the control system is described below in four
distinct phases of operation. For explanatory purposes,
this description will apply to a compressor with an operat-
ing range of 100 to 110 psig (6.9 to 7.6 bar). A compressor
with any other p
ressure range would operate in the same
manner except stated pressures.
Start mode—0 to 50 psig (0 to 3.5 bar)
When the controller (Start) pad is depressed, the
separator/sump tank pressure will quic
kly rise from 0 to
50 psig (0 to 3.4 bar). The compressor initially
starts
unloaded with the solenoid valve open and the inlet valve
closed. It then switches to full load when full rpm has
been achieved. During this period, both the pressure reg-
ulator and the solenoid valve are closed, the inlet valve is
fully ope
n and the compressor pumps at full rated capac-
ity. The rising compressor air pressure is isolated from
th
e service line in this phase by the minimum pressure
valve set at approximately 50 psig (3.4 bar).
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
co
mpressed air to flow into the service line. From this
point on, the line air pressure is continually monitored by
the controller. The pressure regulator and the solenoid
valve remain closed during this phase. The inlet valve is
in the fully open position as long as the compressor is
running at 100 psig (6.9 bar) or below.
Modulating mode—100 to 110 psig (6.9 to 7.6 bar)
If less than the rated capacity of compressed air is being
used, the service line pressure will rise above 100 psig
(6
.9 bar). The pressure regulator valve gradually opens,
d
irecting air pressure to the inlet control valve, reducing
air entering the compressor until it matches the amount
of air being used. The control system functions continu-
ally in this manner between th
e limits of 100 to 110 psig
(6.9 to 7.6 bar) in response to var
ying demands from the
service line. The integrated inlet valve has an orifice
which vents a small amount of air to the compressor inlet
when the pressure regulator controls the inlet control
valve. The orifice also bleeds any accumulated moisture
from the control lines.
Unload mode—in excess of 110 psig (7.6 bar)
When a relatively small amount or no air is being used,
the service line pressure continues to rise. When it
exceeds 110 psig (7.6 bar), the controller control
system
de- energizes the solenoid valve allowing separator/
sump tank air pressure to be supplied directly to close
the inlet valve. Simultaneously, the solenoid valve sends
a pneumatic signal to the blowdown valve. The blow-
down valve opens to the atmosphere, located in
the com-
pressor separator/sump tank, reducing the separator/
sump
tank pressure to approximately 17 psig (1.2 bar).
T
he check valve in the air service line prevents line pres-
sure from returning to the separator/sump tank.
When the line pressure drops to the low setting (cut-in
pr
essure; usually 100 psig (6.9 bar) on low pressure
(7 bar) compressors and 125 psig (8.6 bar) on high pres-
sure (9 bar) compressors, 150 psig (10.3 bar) on (10 bar)
comp
ressors, 175 psig (12.0 bar) on (12 bar) compres-
sors), the controller energize
s the solenoid valve and
allows the blowdown valve to close. The re- energized
solenoid valve again prevents line pressure from reach-
ing the inlet control valve. Sho
uld the pressure begin to
rise, the pressure regulator will resume its normal func-
tion as previously described.
Load / no load control
If desired by the customer, the compressor can be set to
operate load/no load without modulating control. This
control mode is often selected when a large amount of
compressed air storage (air tank) is available. Using the
controller keypad, select Modulate from the menu and
set it to NO. On a machine rated for 100 psig (7 bar) the
compres
sor will run in the full load mode up to 100 psig
(7 bar). If less than the rated capacity is required, pres-
sure will rise above 100 psig and the controller will de-
en
ergize the solenoid valve, causing the compressor to
run in the unload mode. When the system pressure falls
to 90 psig (6.3 bar), the controller energizes the solenoid
valve, cau
sing the compressor to return to the full load
mode. The compressor will thus operate to keep the sys-
tem pressure in the range of 90 – 100
psig (6.3 –
6.9 bar).
Automatic operation
For applications with varied periods of time when there
are no air requirements, the controller’s AUTOMATIC
mode allows the compressor to shutdown (time delayed)
when no compressed air requirement is present and
restart as compressed air is needed.
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