TM-5-3805-254-14-P-2
TRUCK, DUMP, 20 TON, 6X4, ON-OFF HIGHWAY 71,000 GVW, IHC MODEL F-5070 (CCE)
TECHNICAL MANUAL; OPERATOR’S, ORGANIZATIONAL, DIRECT SUPPORT, GENERAL SUPPORT AND DEPT MAINTENANCE MANUAL (INCLUDING REPAIR PARTS INFORMATION AND SUPPLEMENTAL MAINTENANCE INSTRUCTIONS)
JUNE 1980
TM-5-3805-254-14-P-2 - Page 545 of 894
TRUCK SERVICE MANUAL
FUEL SYSTEM
Aneroid
Aneroid Adjustments
Aneroids must not be removed, disconnected or otherwise
rendered ineffective on these engines, nor should settings be
altered to exceed those specified for the aneroid as shown In
Table 521.
Description
1.
During
acceleration
or rapid engine
load changes,
turbocharger speed
(intake manifold
pressure) change
inherently lags behind the power or fuel demand exercised by
opening of the throttle.
2.
This lag does not exist in fuel system.
therefore, an
over rich or high fuel to air ratio, usually accompanied by
heavy smoke, , occurs until the turbocharger
“catches up "
3.
The function of the aneroid is to create a lag In fuel
system
so response is equivalent to that of turbocharger, thus
controlling engine smoke level.
Fuel Flow
1.
Fuel from outlet side of fuel pump enters aneroid and
goes through starting check valve area (5, Fig.
522).
Aneroid
AR40600 series does not have a starting check valve but must
have a fuel check valve in supply line.
2.
The starting check valve (3) prevents aneroid
from
bypassing fuel at engine cranking speeds.
For speeds above
cranking,
fuel
pressure
forces
the
check
valve open,
allowing fuel to flow to valve port (4) of shaft (9)
3.
Shaft (9) and Its bore form the bypass valve This
shaft and
bore allow passage or restriction of fuel flow
in a
similar manner as throttle shaft and sleeve In PT fuel pump
4.
allowed to pass through bypass valve is returned (2)
to
suction
side
(inlet
fitting) of
PT
gear pump
The
bypassed fuel reduces fuel pump output to engine and
reduces fuel manifold pressure In proportion to the bypass
rate.
Fig.
521.
5.
The shaft and sleeve are bypassing fuel when arm
(10) of lever is resting against adjusting screw (1).
The
amount of fuel bypassed is adjusted by this screw, which
protrudes from bottom of aneroid.
6.
The lever arm connected to piston (8) by actuating
shaft (6)., rotates shaft, closing valve port.
The lever is rotated
by action of air Intake manifold pressure (11) against piston
and
diaphragm
(7), moving
actuating
shaft
downward
against resisting spring force.
Fig.
522.
7.
Anytime engine Intake manifold air pressure is above
preset bellows "air actuation pressure," aneroid is "out of
system.
8.
The aneroid begins dumping when Intake manifold air
pressure drops below preset value as happens after
deceleration In traffic, deceleration during gear shifts, down
grade motoring with closed throttle or down grade operation on
light load portion of governor droop curve.
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