PRINCIPLES GASOLINE/DIESEL FUEL SYSTEMS - OD1620
- LESSON 1/TASK 2
(b) The inlet check valve will seat, keeping gasoline from being
pumped back to the float bowl.
(c) The outlet check ball will be forced off its seat, allowing
the gasoline to pass to the pump discharge nozzle where it will be
discharged into the throat.
(d) The pump is raised in the chamber when the throttle valve is
closed, causing the outlet check ball to seat, blocking the passageway.
(e) The inlet check ball is pulled off its seat and gasoline is
pulled into the chamber from the float bowl.
(f) The pump chamber is filled with gasoline and ready to
discharge whenever the throttle valve is opened.
(3) Diaphragm Pump (figure 20 on the following page). The diaphragm
type pump system works similarly to the pistontype, with the exception of
the pump design which includes a flat rubber diaphragm. By flexing this
diaphragm, a pressure differential is created that results in pump action.
(4) Controlling Pump Discharge. The linkage between the accelerator
pump and the throttle cannot be solid. If it were, the pump would act as a
damper, not allowing the throttle to be opened and closed readily. The
linkage usually activates the pump through a slotted shaft or something
similar. When the throttle is closed, the pump is held up by its linkage.
When the throttle is opened, the pump is activated by being pushed down by a
spring, called a duration spring.
The tension of the duration spring controls the length of time that the
injection of fuel lasts. The spring is calibrated to specific applications.
Too much spring pressure will cause fuel to be discharged too quickly,
resulting in reduced fuel economy. Too little spring pressure will cause
fuel to be discharged too slowly, resulting in engine hesitations.
e. Choke System.
(1) Purpose. When the engine is cold, the gasoline tends to condense
into large drops in the