PRINCIPLES GASOLINE/DIESEL FUEL SYSTEMS - OD1620 - LESSON 1/TASK 2
chamber to cushion the pulsating action inherent to the diaphragmtype pump.
(10) An oil seal is provided to keep crankcase oil from entering the
lower chamber and leaking from the venthole.
d. Mechanical, Positive Type. The positivetype mechanical pump
operates in the same manner as the nonpositivetype. The difference is that
the diaphragm pull rod is solidly linked to the rocker arm. The pump,
therefore, will not regulate fuel line pressure. When this type of pump is
used, a separate fuel pressure regulation device must be employed which will
bypass excess fuel back to the fuel tank.
e. Double Action Fuel Pump (figure 5). Vehicles that use vacuum
operated windshield wipers will often use a supply pump that is built into
the fuel pump. The pump serves to operate the windshield wipers during
periods of high engine load when the
FIGURE 5. DOUBLE ACTION PUMP.