PRINCIPLES GASOLINE/DIESEL FUEL SYSTEMS - OD1620 - LESSON 2/TASK 2
as well as the maximum and idle speeds. The mechanical 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 will restrict fuel to the injectors above maximum
rated rpm. The idle springs (in the governor spring pack) position 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 injector in accordance with the engine requirements, as
controlled by the throttle and limited by the size of the idle spring
plunger counterbore on the PTG fuel pumps. When the engine reaches governed
speed, the governor weights move the governor plunger, and fuel flow to the
injectors is restricted. At the same time, another passage opens and dumps
the fuel 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 shutdown valve, inlet supply lines,
and into the injectors.
(c) 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 PTG 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
(d) The fuel shutdown valve is located on top of the fuel pump.
It shuts off fuel to the injectors. With the master switch on, the solenoid
opens the valve. With the switch off, the spring loaded valve returns to
the OFF position. In case of an electrical failure, rotation of the manual
knob clockwise will permit fuel to flow through the valve. The knob is
located on the front valve.
(3) PTD Injectors. A PTD injector is provided at each engine
of the unit