2: Description 600H, 750, 750H, 750HH, 825, 900, 900H, 1050 T3 CAT User Manual
02250197-981 R01
22 Subject to EAR, ECCN EAR99 and related export control restrictions.
2.5 Capacity control system,
functional description
Refer to Figure 2-4. The purpose of the control system is
to regulate the amount of air intake in accordance with
the amount of compr
essed air demand. The control sys-
tem consists of an inlet valve, the high and low pressure
regulato
rs, the pressure reducing regulator, the blow-
down/ running blowdown valve, the Compass
®
Control-
ler, a START/RUN selector switch, and the HIGH/LOW
selec
tor switch.
2.5.1 Start—0 to 65 psig (0 to 4.5 bar)
Push OFF/ON/START switch to “ON” position to initialize
the Compass Controller. Once the Compass Controller
says “READY” on LCD, press OFF/ON/START switch to
the “START” position. In the “START” position, the inlet
valve is held closed by the springs in the inlet valve. The
valve is cracked open by vacuum in the compressor and
is allowed to build up to 65 psig (4.5 bar). The reason for
keeping the valve closed during start is to allow the
engine to warm up without being loaded by the compres-
sor. Air pressure is contained in the receiver tank by the
min
imum pr
essure valve which has a set point of 65 psig
(4.5 bar). At this point the valve opens allowing the air to
pass to the service valve. After engine has warmed up
the machine automatically transfers to “RUN” mode.
2.5.2 Low pressure—80 to 100 psig (5.5 to
6.9 bar)
With the HIGH/LOW switch in the “LOW” position, and
the controller in “RUN” mode, the service valve can now
be opened. Pressure from the 60 psig (4.1 bar) reducing
regulator opens up the inlet valve and the Compass Con-
troller increases the engine speed to full load (1800 rpm).
As the demand
for air decreases, the Compass Control-
ler commands the engine to reduce speed to idle (1400
rpm) and the inlet valve closes, where it st
abilizes until
the air demand is required again. If the machine is not
marked with an “H” or “HH”, it is a single pressure
machine and will not have a HIGH/LOW switch. The
machine will run as if it is in the “LOW” position.
2.5.3 High Pressure—80 to 150 psig (5.5 to
10.3 bar) for “H” models or 80 to 175
psig (5.5 to 12.1 bar) for “HH” models
When the HIGH/LOW switch is switched to the “HIGH”
position, the low pressure regulator is blocked off allow-
ing the high pressure regulator to take over control of the
mach
ine. The 60 psig (4.1 bar) reducing regulator fully
opens the inlet valve and the Compass Controller com-
mands maximum speed (1800 rpm) from the engine. As
the
pressure
reaches the set point of the system the high
pressure regulator cracks open and closes the inlet valve
and the Compass Controller returns the engine back to
idle, until a demand for air is seen.
2.5.4 Shutdown
The blowdown valve is normally closed. When the com-
pressor is shutdown, system pressure
backs up to the
inlet valve causing the check spring in the inlet valve to
close the air inlet valve. This sends a pressure signal to
the blowdown valve causing it to open and vent the pres-
sure in the system. After the pressure is vented, the
blo
wdown va
lve spring returns the blowdown valve to the
closed position.
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