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 502 of 894
TRUCK SERVICE MANUAL
FUEL SYSTEM
Gear Pump And Pulsation Damper
The gear pump is driven by the pump main shaft and
contains a single set of gears to pick-up and deliver fuel
throughout the fuel system.
A pulsation damper
mounted to the gear pump contains a steel diaphragm
which absorbs pulsations and smooths fuel flow through
the fuel system.
From the gear pump, fuel flows through the filter screen
and.
In the PT (type G) fuel pump, to the governor
assembly as shown in Fig. 5-3.
Currently, PT (type G) gear pumps are equipped with a
bleed line (to the engine injector return line or to tank)
which prevents excessive fuel temperatures within the
fuel pump.
The bleed line functions primarily when the
pump throttle is set at Idle speed but when gear pump
output is high, due to engine rotative speed, as occurs
during down hill operation.
A special check valve and/or
fitting is used In the gear pump to accomplish the bleed
action.
Pressure Valve
The pressure valve is used only In PT (type G) VS
governor fuel pump.
The valve is located near gear
pump drive shaft.
It restricts return fuel coming from
governor barrel thereby creating low fuel pressure in
housing.
Throttle
In both fuel pumps, the throttle provides a means for the
operator to manually control engine speed above Idle as
required by varying operating conditions of speed and
load.
In the PT (type G) fuel pump, fuel flows through the
governor to the throttle shaft.
At idle speed, fuel flows
through the idle port in the governor barrel, past the
throttle shaft.
To operate above idle speed, fuel flows
through the main governor barrel port to the throttling
hole in the throttle shaft.
Shut-Down Valve
Either a manual or an electric shut-down valve is used on
Cummins fuel pumps.
With a manual valve, the control lever must be fully
clockwise or open to permit fuel flow through the valve.
With the electric valve, the manual control knob must be
fully counterclockwise to permit the solenoid to open the
valve when the "switch key" is turned on.
For emergency
operation in case of electrical failure, turn manual knob
clockwise to permit fuel to flow through the valve.
Governors
Idling And High-Speed Mechanical Governor
The mechanical governor, sometimes called "automotive
governor," is actuated by a system of springs and
weights, and has two functions.
First, the governor
maintains sufficient fuel for idling with the throttle control
in idle position; second, it cuts off fuel to the injectors
above maximum rated rpm.
The idle springs in the
governor spring pack positions the governor plunger so
the idle fuel port is opened enough to permit passage of
fuel to maintain engine idle speed.
During operation between idle and maximum speeds,
fuel flows through the governor to the injectors in accord
with the engine requirements as controlled by the throttle
and limited by the size of the idle spring plunger
counterbore on PT (type G) fuel pumps.
When the
engine reaches governed speed, the governor weights
have moved the governor plunger to close the fuel
passages to injectors.
At the same time another
passage is opened and fuel is dumped back into the
main pump body.
In this manner engine speed is
controlled and limited by the governor regardless of
throttle position.
Fuel leaving the pump flows through the
shut-down valve, supply lines and cylinder head drillings
into the injectors.
Removal Of Fuel Pump Units
Clean And Mount
1.
Clean outside of fuel pump thoroughly with an
approved solvent.
Remove lockwires and seals if used.
Note
:
Many solvent cleaners are injurious to aluminum.
Make sure your cleaner is suitable before using it on
aluminum.
2.
Remove pulsation damper from gear pump and
discard "0" ring.
Older style dampers are fitting mounted
and are removed by screwing damper from fitting on
gear pump,
3.
To remove gear pump from main housing, tap sides
of gear pump with a plastic hammer to loosen from
dowel.
Remove gear pump discard gasket.
PT (type G) Fuel Pump Service Cooling Kit
1.
Remove check valve and orifice elbow assembly
from bottom or back side of fuel pump.
Note
:
Current pumps have the check valve located at
the gear pump and older pumps should be changed over
at any time a new gear pump is used.
2.
Clean parts in clean fuel oil and dry with compressed
air blown through both ends.
Shut-Down Valve, Pulsation Damper And Gear Pump
1.
Remove shut-down valve from top of main housing
and discard "O" ring.
497
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