Section 2
DESCRIPTION
16
MODULATION - 100 TO 110 PSIG (6.9 TO 7.6
BAR) OR 150 TO 165 PSIG (10.3 TO 11.4 BAR)
FOR “H” MACHINES
Should less than the rated capacity of air be used,
the service line pressure will rise above 100 psig
(6.9 bar) low or single pressure rating, 150 psig
(10.3 bar) dual or high pressure rating. The pres-
sure regulating valve gradually opens, applying
pressure to the inlet valve piston and speed control
cylinder . This causes the inlet valve to partially
close and reduces the speed of the engine. As the
pressure increases, the inlet valve piston will further
close the inlet valve and continue reducing the
speed until it reaches a pre-set idle speed. Now as
air demand increases, the sump pressure will fall
below the 110 psig (7.6 bar) or 165 psig (11.4 bar)
for “H” machines.
The pressure regulating valve will close, the air inlet
valve will fully open and the engine will once again
run at a pre-set full load speed.
Between the pressure regulating valve and inlet
valve, a small orifice is installed which vents a small
amount of air to the atmosphere, when the pressure
regulating valve is open. This allows variance of air
output to match air demand. The orifice also bleeds
any accumulated moisture from the regulator.
SHUTDOWN
The blowdown valve is normally closed. Upon shut-
down, the back pressure in the compressor inlet
signals the blowdown valve to vent the sump pres-
sure to the atmosphere.
2.7 AIR INLET SYSTEM, FUNCTIONAL DESCRIP-
TION
Refer to Figure 2-5A or 2-5B. The air inlet system
consists of two air filters, a compressor air inlet
valve and interconnecting piping to the engine
and compressor.
The air filters are two-stage dry element-type filters.
These filters are capable of cleaning extremely dirty
air. However, in such cases, frequent checks of the
air filter will be required.
See Section 5 for Air Filter Maintenance
Procedures.
2.8 INSTRUMENT PANEL GROUP, FUNCTIONAL
DESCRIPTION
Refer to Figure 2-6. The instrument panel group
consists of a molded panel containing an air pres-
Figure 2-5A Air Inlet System - Caterpillar and Perkins Models
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