TM 55-2835-209-23
1-16 CONTROLS AND ACCESSORIES
a.
The controls and accessories
section includes those ele-
ments required for proper APU
operation:
electronic se-
quence unit (ESU), fuel sys-
tem, lubrication system and
ignition system.
The APU is
equipped with a fully-
automatic control system that
properly sequences control of
fuel and ignition during
starting and operation.
All
APU speed control, switching
and protection functions are
controlled by the ESU which is
mounted separately from the
APU.
APU speed is regulated
by a signal from the. ESU to
the fuel control torque motor
assembly which provides deliv-
ery of the correct amount of
fuel regardless of ambient
conditions and load require-
ments.
Overspeed protection
is provided by an electronic
overspeed switch that is auto-
matically actuated if re-
quired.
b.
The fuel system contains com-
ponents which function auto-
matically to provide proper
starting and acceleration to
maintain constant APU speed
under all operating
conditions.
Components of the
fuel system are: fuel filter
assembly, fuel control assem-
bly, fuel solenoid valve, fuel
manifold assembly, fuel check
valve and three primary and
three secondary fuel nozzle
assemblies.
c.
The lubrication system pro-
vides lubrication for all
gears, shafts and bearings
within the APU. The lubri-
cation system consists of an
oil pump, oil filter element,
low oil pressure switch, oil
temperature bulb, magnetic
drain plug, fill to spill plug
and oil fill cap with dip-
stick.
The system oil pump
maintains operating oil pres-
sure.
d.
The electrical system provides
automatic actuation in proper
sequence of the circuits which
control APU starting, ig-
nition, acceleration, fuel
flow and monitoring. Compo-
nents of the electrical system
include ignition unit, igniter
plug lead, igniter plug assem-
bly, motional pickup trans-
ducer, hourmeter assembly,
thermocouple, APU and fuel
control wiring harness assem-
blies.
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