FUEL SYSTEM MAINTENANCE
mechanism. A variable-stroke pump is shown in
The most important consideration in working
An engine-driven rotary-vane type of pump
with any fuel system maintenance task is the
and a diagram showing the operation of the unit
safety of personnel. Aircraft fuels are extremely
are shown in figure 4-28.
hazardous because of the explosive and toxic
dangers that are always present. The health
The engine-driven fuel pump is turned by a
hazards associated with aviation fuels (breathing
gear train in the accessory section of the engine.
of vapors, spillage on skin or in the eyes, or
Constant pressure is maintained by a spring-
swallowing) must be avoided. It is not possible
loaded pressure relief valve. Figure 4-28 shows the
to describe all the potential problems or dangers
pressure relief valve in operation, bypassing
that may arise in the performance of any type of
excess fuel back to the inlet side of the pump.
fuel system maintenance. As an AD, it is your
Fuel is bypassed before the engine is started,
responsibility to be thoroughly aware of all the
when the engine-driven fuel pump is not turning.
safety practices and procedures that must be
An auxiliary fuel booster pump delivers fuel under
pressure. Fuel pumped by the booster pump will
Fuel vapors are very harmful when they are
pass through the stationary engine-driven pump;
inhaled. It takes only a very small percentage of
it is necessary to incorporate a bypass valve in the
these vapors to cause very serious effects on
engine-driven pump. Both the fuel pressure relief
personnel. Fuel vapors are heavier than air and
valve and the bypass valve may be contained in
will collect in the lower areas of the fuel tank/cell.
the same mechanism.
Unless these vapors are removed by the use of
forced-air ventilation, they can present a hazard
Refer to Fluid Power, NAVEDTRA 12964,
for an indefinite period. Personnel should avoid
for a detailed description of the principles of
the inhalation of these vapors, and always be alert
operation of the various types of pumps.
Figure 4-28.-Engine-driven, rotary-vane type of pump.