(c)
Make sure there are no bubbles, defects, or small holes in the paint.
(d)
Make sure the paint thickness is not less than 0.03 inch (7.6 mm).
S 418-014
(6)
Close the APU access doors:
(a)
Do a visual check of the EGT bus bars:
1) Make sure the bus bars are not damaged.
2) Make sure no metal parts touch the bus bars.
3) Make sure the bus bars do not touch each other.
(b)
Disengage the support rods on the APU access doors.
(c)
Put the support rods in the clips on the inner side of the APU access doors.
(d)
Make sure the insulation covers correctly attach to the APU compartment firewall.
(e)
Close the APU access doors.
(f)
Close the latches on the APU access doors.
S 868-020
(7)
Remove the DO-NOT-CLOSE tags and close these circuit breakers:
(a)
P6 Main Power Supply Panel
1) 6K18 APU ALTN CONT
(b)
P83 Panel, E8 Aft Equipment Center
1) APU PRIMARY CONT
S 868-021
(8) Remove the DO-NOT-OPERATE tag from the APU control switch on the P5 panel.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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747-400 MAINTENANCE MANUAL
APU ENGINE LUBRICATION SYSTEM - DESCRIPTION AND OPERATION
_________________________________________________________
General
_______
A. The lubrication system supplies lubricating oil to the bearings, gears and generator drive splines. Oil flow rate is 64 pounds/minute at a constant pressure of 80 |5 psig. The oil flow lubricates and cools the bearings and carries foreign matter to the oil filter where it is retained. The oil tank is integral with the load gearbox and is of the 'hot tank' type, as scavenge oil is not cooled before returning to the tank. The total capacity of the oil tank is 4.81 U.S. gallons (18.2 liters). The oil quantity that can be used is 4.2 U.S. gallons (15.9 liters).
Oil Filter (Fig. 1)
__________
A. Pressure oil enters the oil filter from the air cooled oil cooler and flows on to the load gearbox. The oil filter consists of a filter cover assembly, filter element and attaching hardware. The oil filter is located on the right hand side of the accessory gearbox below the air inlet plenum.
Chip Detectors (Fig. 1)
______________
A. Two bayonet type magnetic chip detectors are installed on the APU. One is located on the bottom right side of the accessory gearbox and the other is located on the bottom left side of the load gearbox near the drain collector bracket. The chip detectors are intended to be used as a trouble shooting aid and not as a conditional monitoring tool.
Operation (Fig. 2)
_________
A. Pressure Oil System
(1)
Oil drawn from the tank by the pressure pump is routed through a filter screen to the pressure regulating valve (PRV) inlet of the oil filter assembly. The cold start valve provides a safeguard against excessive pressure buildup due to cold weather operation. The valve opens and diverts oil to the pump inlet via internal cored passages in the pump housing should the oil pressure exceed 200 psi. The pressure regulating valve also bypasses pressure oil to the pump inlet, thereby maintaining a constant oil system pressure.
(2)
Oil from the PRV flows through an oil filter to the fuel cooled oil cooler (FCOC) which is mounted on the oil filter assembly. Primary cooling of the lubricating oil is carried out by the FCOC which transfers heat from the oil to the incoming fuel. A check valve installed upstream of the filter prevents oil leakage when the cooler is removed. A bypass valve is fitted in the oil stream to limit maximum oil pressure drop through the cooler.
(3)
Pressure oil from the FCOC flows through external tubing to the air cooled oil cooler (ACOC). The ACOC provides secondary cooling for the lubricating oil. Heat from the oil is transferred to air from the cooling fan. A thermal/pressure relief valve is fitted integrally with the ACOC oil inlet/outlet ports. The ACOC oil return tube is connected to the load gearbox through an anti siphon oil nozzle strainer. An oil pressure switch and temperature sensor, fitted in the oil stream, provide signals to the APU Controller. An external tube routes pressure oil to a boss at the 11 o'clock position on the load gearbox.
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