PRINCIPLES GASOLINE/DIESEL FUEL SYSTEMS - OD1620 - LESSON 2/TASK 2
pressure developed in the pump chamber unseats the delivery valve.
flows into the distribution chamber and is sent by the slot in the plunger
to whatever injector is scheduled to receive it.
(g) The amount of fuel delivered by each injection charge will
increase proportionately as the plunger sleeve is moved from its extreme
downward to its extreme upward position. The higher the plunger sleeve, the
longer the effective pump stroke (plunger movement before the spill port is
pressure for the following reasons:
(1) The injection pumps lack the suction ability to draw fuel from
the tank by themselves.
(2) It is important to supply fuel in excess to the injection pump so
that fuel may be used to cool and lubricate the system before bypassing it
back to the tank.
(3) Without a supply pump, the system would lose its prime whenever
the pump is in no-delivery mode.
The supply pumps in use generally are of the positive displacement type with
a performance that is independent of any reasonable variations in viscosity,
pressure, or temperature of the fuel. In a majority of the equipment, the
fuel supply pump is built into the injection pump unit. This cuts down on
fuel tubing and the complexity of the equipment, and allows the supply pump
to share the same engine power takeoff as the injection pump.
b. Vane-Type Supply Pump. The basic overall operation of the vane-type
supply pump is the same as the vane-type oil pump.
c. Plunger-Type Supply Pump (figure 57 on the following page).
(1) This type of pump is always mounted on the injection pump, where
it is driven by the injection pump camshaft. It is a variable-stroke, self-
regulating pump that will build pressure only up to a predetermined point.