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TM 9-8000
Figure 4-12. Bellows-Type Electric Fuel Pump.
the armature down and repeat the pumping process.
(1) As electric current is fed to the pump, the
(6) The pump will stop when the fuel pressure is high
electromagnetic coil pulls the armature down, expanding
enough to hold the bellows expanded against the return
the bellows.
spring. The operating pressure of  the pump Is
determined by the return spring pressure.
(2) The expansion of the bellows causes fuel to be
drawn In through the inlet valve.
g. Electric, Vane-Type (Fig. 4-13). The 48 vane-type
electric fuel pump operates by the same principles as the
(3) As the bellows are fully expanded, a pair of contact
pump described in paragraph 20-6. It is driven by an
points are open, switching off the electromagnet.
electric motor.
(4) The return spring pushes the armature back up,
4-4. Fuel Tank Ventilation Systems.
contracting the bellows. This action pushes the fuel out
a. Purpose. The fuel tank needs a ventilation system to
of the pump through the outlet valve.
keep the pressure within it equal to
(5) The contact points are closed as the bellows are
fully contracted. This causes the electromagnet to pull
Figure 4-13. Vane-Type Electric Pump.


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