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3.11.11 Fuel feed pump
(1) Feature
Fuel feed pump is double action piston type with four
check valves. It is installed on the side of the injection
pump and driven by a cam.
The feed pump sucks up fuel from the fuel tank and sends
it to the fuel injection pump through a fuel filter. It also
automatically adjusts the fuel delivery pressure.
Two oil seals are used on the push rod to prevent lube oil
from mixing with the fuel from entering the cam cham-
ber.
(2) Double action piston and automatic pressure
control mechanism
When the piston moves upward, the pressure in the
upper chamber rises and the pressure in the lower cham-
ber becomes negative. As to the check valve in the upper
chamber, right vale is closed and left valve is opened.
Thus, the fuel is delivered to the outlet.
As the pressure in the lower chamber is negative, left
valve in the lower chamber is closed and right valve is
opened, and then fuel flows into the lower chamber.
When piston moves downward, the pressure in the lower
chamber rises and left check valves are opened and right
valves are closed, and then fuel in the lower chamber is
delivered to the outlet.
When the delivery pressure of the fuel pump rises up to
the extent that the pressure at the back of the piston over-
comes the piston spring force, the movement of the pis-
ton is hindered.
Thus, the fuel flow is automatically stopped, and the fuel
pressure is maintained within a fixed range.
- 3-43-13 -
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