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 hydroxide.
 c)  Fully clean the solid.
 d)  Make a saturated solution of the solid in ammonium
 hydroxide.
 2)  Put the element in the saturated solution at the ambient
 temperature for 60 minutes.
 a)  Flush the element in hot water at 150-200°F (66-93°C)
 for 1-5 minutes. b) Dry the element with the air for 1-3 minutes.
 (c)  If there are copper particles, do these steps: 1) Remove the copper particles on the element end caps with a
 5-10 percent nitric acid solution. 2) Flush the element with pressure in cold water. 3) Dry the element with the air.
 S 227-012
 (4)  
Examine the element for broken wires or cracks in the epoxy bonds.

 (a)  
Look at the element with a magnifying glass (10 power). 1) Replace the element if the wires are broken. 2) Replace the element if the epoxy bonds are damaged. 3) Sharp or large dents are permitted if the wires are not

 broken.
 NOTE: Do not try to remove sharp or large dents.
____
 S 797-013
 (5)  
Do the bubble point test.

 (a)  
Put the element 0.5 inches (1.3 cm) below the surface of the cleaning fluid, 72°F (22°C) maximum.

 (b)  
Slowly increase the pressure in the ultrasonic sump.

 NOTE: If you increase the pressure too quickly, you will
____ make ambient vibrations in the ultrasonic sump.
 (c)
Turn the element slowly until the first air bubble shows.

 1)  If the bubble shows when the pressure is less than 8 inches of water on the gage, replace the element.

 (d)  
Dry the element with the air for 1-3 minutes.

 S 937-014
 (6)  
Use the engraver to write the date adjacent to the part number on the element.

 (7)  
Put the element into a clean polyethylene bag until you install it.

 S 557-015
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400 MAINTENANCE MANUAL
 S 427-018
 (8)  Do this task: P3 Air Filter Element Installation (AMM 49-52-08/401).
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
 1.

2.

3.

4.

5.

A
747-400 MAINTENANCE MANUAL
 APU CONTROL SYSTEM - DESCRIPTION AND OPERATION
______________________________________________
General
_______
 A.  The APU controls consist of manual and automatic controls for starting, stopping, and maintaining the APU within safe limits during APU operation. Once an APU start is obtained, further control of the unit is fully automatic. The controls consist of speed sensors, exhaust gas thermocouples, trim box, air and pressure sensors and a serial number identification unit. Electrical power for the APU control circuit is 28 volts dc.
 B.  The APU controls transmit signals to the APU controller for processing. The APU controller transmits information via the ARINC 429 data bus, for read out on the Engine Indicating and Crew Alerting System (EICAS) display in the flight deck.
Speed Sensors (Fig. 1)
_____________
 A.  The load compressor (N1) and gas generator (N2) speed sensors are both dual coil pulse pick-up sensors. The No. 1 coil in each sensor is for controlling the APU and No. 2 coil is for overspeed protection. The N1 sensor measures the speed of the load gearbox input shaft and the N2 sensor measures the speed of the oil pump drive.
Exhaust Gas Thermocouples (Fig. 1)
_________________________
 A.  There are six exhaust gas thermocouples (T6) located in the gas path downstream of the power turbine. The T6 signal is corrected in the APU controller for trim and ambient conditions to ensure that turbine entry temperature limitations are not exceeded. The thermocouples are K type (chromel/alumel) and sheathed. The thermocouple tips are swaged down for fast response. Each thermocouple is connected to circumferential busbars by pigtails.
　
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