TM 5-3805-248-23-1
THEORY OF OPERATION - CONTINUED
0003 00
FUEL SYSTEM
0003 00
Fuel Tank. The fuel tank, which has a 135-gallon capacity, is mounted on the tractor portion of the 621B Scraper, on the
1.
right side of engine compartment. Fuel level is indicated by dipstick located inside fuel cap.
Fuel Pump. The fuel pump is mechanically driven by the engine and provides a low pressure fuel supply to the fuel
2.
injection pump housing.
Fuel Filters (Primary and Secondary). The fuel is pulled through the primary fuel filter to fuel pump and passed along
3.
under low pressure to the secondary fuel filter.
Priming Pump. The priming pump, part of the primary fuel filter housing, is used for bleeding the fuel lines after
4.
replacement of fuel filter elements. This pump must not be used while the engine is running. The pump has a locking
position which disables it under normal conditions.
Anti-Siphon Block. The anti-siphon block ensures the injection pumps a positive head of fuel pressure while in opera-
5.
tion and eliminates the possibility of over-pressurizing the low pressure lines. When the 621B Scraper is off, it elimi-
nates the siphon effect on the fuel lines, which would cause a no-fuel and no-start condition.
Injection Pump Plungers. Six injection pump plungers and lifters are internally cam-actuated and mounted in the
6.
injection pump housing. The injection pump plungers are scroll type, with fuel quantity being controlled by a turning,
calibrated plunger.
Fuel Injection Nozzles. Six fuel injection nozzles are installed in direct injection adapters mounted in the cylinder head.
7.
These injection nozzles are connected to the injection pump-plungers, where fuel is time-injected under high pressure
with a specific fuel pattern for good combustion in the cylinders.
INJECTION
PUMP
PRIMING
ANTI-SIPHON
PUMP
BLOCK
FUEL
INJECTION
INJECTOR
NOZZLES
NOZZLES
SECONDARY
FUEL
FILTER
FUEL
TANK
394-1601
FUEL
PRIMARY
FUEL
PUMP
FILTER
0003 00-2
