THEORY OF OPERATION - CONTINUED
Fuel Tank. The fuel tank, which has a 135-gallon capacity, is mounted on the tractor portion of the 621B Scraper, on the
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
injection pump housing.
Fuel Filters (Primary and Secondary). The fuel is pulled through the primary fuel filter to fuel pump and passed along
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
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-
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
injection pump housing. The injection pump plungers are scroll type, with fuel quantity being controlled by a turning,
Fuel Injection Nozzles. Six fuel injection nozzles are installed in direct injection adapters mounted in the cylinder head.
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.