PRINCIPLES GASOLINE/DIESEL FUEL SYSTEMS - OD1620 - LESSON 2/TASK 2
PRESSURE-TIMED GEAR PUMP.
(a) The gear-type pump draws fuel from the supply tanks and forces
it through the pump filter screen to the governor. It is driven by the pump
main shaft and picks up and delivers fuel throughout the fuel system.
pulsation damper mounted to the gear pump contains a steel diaphragm that
absorbs pulsations and smooths fuel flow through the fuel system. From the
gear pump, fuel flows through the filter screen to the governor screen. The
PTG pumps are equipped with a bleed line that is attached to the engine
injector return line or to the tank.
This prevents excessive fuel
temperature within the fuel pump by using the surplus fuel as a coolant.
The bleed line functions primarily when the pump throttle is set at idle
speed, but gear pump output is high due to engine operating speed, as occurs
during downhill operation. A special check valve and/or fitting is used in
the gear pump to accomplish the bleed action.