(a)
P6 Main Power Supply Panel
1) 6K18 APU ALTN CONT
(b)
P83 Panel, E8 Aft Equipment Center
1) APU PRIMARY CONT
S 016-001
(3)
Open the APU access doors.
(a)
Open the latches on the APU access doors.
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747-400 MAINTENANCE MANUAL
(b)
Open the APU access doors.
(c)
Engage the support rods for the APU access doors.
S 216-010
(4)
Examine the exhaust V-band clamp.
(a)
Visually examine the V-band clamp for cracks, burrs, or worn areas.
(b)
Examine the V-band to see if it is loose.
(c)
If the V-band is loose, do a torque check as follows: 1) Lightly hit the outer edge of the clamp with a mallet that
is not metal to correctly engage the clamp. 2) Tighten the clamp to 45-55 pound-inches (5.1-6.2 N.m). 3) Do steps 1) and 2) until the clamp nut does not lose its
torque value of 45-55 pound-inches (5.1-6.2 N.m).
S 416-004
(5)
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 for 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 866-007
(6)
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 866-006
(7) Remove the DO-NOT-OPERATE tag from the APU control switch on the P5 panel.
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2.
3.
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747-400 MAINTENANCE MANUAL
APU OIL EXTERNAL DISTRIBUTION SYSTEM - DESCRIPTION AND OPERATION
________________________________________________________________
General
_______
A. The APU oil external distribution system provides primary and secondary engine oil cooling by channeling pressure oil through two externally mounted heat exchange units. The system consists of an air cooled oil cooler (ACOC) and fuel cooled oil cooler (FCOC).
Air-Cooled Oil Cooler (Fig. 1)
_____________________
A. The ACOC is mounted on top of the load gearbox. Oil flow through the ACOC is two-pass, cross-contra and the coolant airflow from the fan is single-pass. The ACOC exchanges heat between the engine oil and the cooling air. A thermal/pressure relief valve, fully open to the bypass under cold conditions, begins to close when oil temperature reaches 150 degrees fahrenheit (66 degrees celsius), and is fuly closed at oil temperatures of 175 degrees fahrenheit (80 degrees celsius) and above. In the event of a pressure drop at the ACOC exceeding 20 psi when the valve is closed under the influence of the thermal element, a pressure relief spring allows the poppet to move so as to re-open the bypass.
Fuel-Cooled Oil Cooler (Fig. 1)
______________________
A. The FCOC is mounted on the oil filter assembly. Drained pressure fuel collects heat from the lubricating oil as the fuel and oil streams each make two passes within the cooler internal matrix. The fuel and oil flow is in opposite directions, giving a contra-flow arrangement. A pressure relief valve assembly is fitted in the oil system so as to limit maximum oil pressure drop through the matrix exceeds a set pressure, the relief valve operates allowing oil to flow through the bypass.
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