Section 2
DESCRIPTION
14
Figure 2 ---5 Air Inlet System
the inlet valve remains fully open for maximum air
output. The engine will continue to run at full speed
during this phase of operation.
MODULATION -- 100 TO 110 PSIG (6.9 TO 7.6
BAR) OR 150 TO 165 PSIG (10.3 TO 11.4 B AR)
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 pressure reg-
ulating valve gradually opens, applying pressure to
the inlet valve piston and speed control cylinder.
This causes the inlet valve to partially close and re-
duces the speed of the engine. As the pressure in -
creases, 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” ma-
chines.
The pressure regulating valve will close, the air inlet
valve will fully open and the engine will once again
runatapre---setfullloadspeed.
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. After the sump pressure
hasvented,theidlewarm---upvalvewillautomati-
cally reset from normal operation mode to start
mode.
2.7 AIR INLET SYSTEM, FUNCTIONAL DESCRIP-
TION
Refer to Figure 2---5. The air inlet system consists of
two air filters,acompressor air inlet valve and in-
terconnecting piping to the engine and compres -
sor.
The a ir filters are 2---stage dry element---type filters.
These filters are capable of cleaning extremely dirty
air. However, in such cases, frequent checks of the
airfilterwillberequired.
See Section 5 for Air Filter Maintenance Procedures.
2.8 INSTRUMENT PANEL GROUP, FUNCTIONAL DE-
SCRIPTION
Refer to Figure 2---6. The instrument panel group
consists of a heavy gauge panel containing an air
pressure gauge, hourmeter, starter pushbutton,
toggle ignition switch, circuit override button,
circuit breaker, warning light for alternator mal -
function, and idle warm- -up button.Ahigh--low
pressure selector switch is located on the panel
for 185H compressors.
Refer t o Figure 2---6 for locations of the following in-
dicators and controls:
S The air pressure gauge continually monitors the
sump pressure at various load or unload conditions.
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