CONTROLS AND ACCESSORIES

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. 1 - 10