Lesson 1/learning Event 1
When the carburetor bowl is filled, a needle valve blocks the flow of fuel. This causes back pressure in the
fuel discharge line and in the pumping chamber of the fuel pump. The diaphragm now has full back
pressure on top of it and diaphragm spring pressure below. When the fuel pressure is the same as that of
the compressed spring, the diaphragm will stop in its intake position (down). At this time, the rocker arm
still pivots up and down, following the camshaft eccentric. However, the rocker arm will no longer move
the link, because they are two separate pieces. (The rocker arm can move the link down, but it can never
push it back up.)
When the carburetor needs more fuel, the needle valve of the carburetor opens, and the back pressure in the
discharge line is relieved. This allows the diaphragm spring to push the diaphragm up, forcing more fuel
into the carburetor past the opened needle valve. As the eccentric on the cam rotates, it causes the
diaphragm to be pulled down again and pumping is resumed.
Electric Fuel Pumps
There are two types of electric fuel pumps used in military wheeled vehicles. These pumps are operated by
either an electric motor or a solenoid.
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