(i)
Position lower shroud against upper shroud and close shroud latches.
CAUTION: MAINTAIN A MINIMUM CLEARANCE OF 0.18 INCH BETWEEN ENGINE PLUMBING, FIRE DETECTOR, CLAMPS, AND INSIDE SURFACE OF LOWER SHROUD.
EXERCISE EXTREME CARE NOT TO DAMAGE SHROUD DRAIN LINES WHEN HANDLING SHROUD.
(j) Disengage APU compartment access door support rods and stow rods. Close and latch access door.
D. High Pressure Fuel Line Purging
(1) Prepare to motor APU.
(a)
Provide airplane with external power.
(b)
Position BATTERY SWITCH to OFF and placard.
(c)
Verify all fuel system boost pump switches are OFF.
(d)
Open APU compartment access door latches and open access door. Install door support rods.
(e)
Support shroud, open shroud latches and remove shroud.
CAUTION: EXERCISE EXTREME CARE NOT TO DAMAGE SHROUD DRAIN LINES WHEN HANDLING SHROUD.
(f)
Disconnect ignition unit power supply electrical connector from ignition unit.
(g)
Disconnect high-pressure fuel line from fuel atomizer and connect fabricated hose. Place free end of hose into container.
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(2) Purge high-pressure fuel line.
(a)
Position No. 1 tank forward boost pump to ON.
NOTE: No. 1 tank boost pump requires AC power. If you must use the fuel boost pumps in the center tank, you must have a maintenance person or observer in the flight compartment to continuously monitor the LOW PRESSURE lights. Turn the applicable fuel boost pump to the OFF position if the LOW PRESSURE light for the center tank stays on.
(b)
Remove placard and position BATTERY SWITCH to ON.
(c)
Motor APU (par. 3.D.).
(d)
Observe fuel flow into container. When fuel flow comes out in steady stream, free of air bubbles, position APU MASTER SWITCH to OFF.
CAUTION: PURGING HIGH PRESSURE FUEL LINES MAY REQUIRE MORE THAN ONE START CYCLE. TO AVOID DAMAGING APU, OBSERVE OPERATING LIMITS (FIG. 201).
(e)
Restore airplane to normal configuration (par. 3.E.).
7. APU Fuel System Leak Check (Fig. 202)
A. General
(1) Test of APU fuel supply system will check the integrity of the system for leaks, which are causing pressure decay.
B. Equipment and Materials
(1)
Pressure gage (0-100 psi)
(2)
Suitable hose
(3)
Bulkhead tee fitting
C. Prepare for APU Fuel System Leak Check
(1)
Position BATTERY SWITCH to OFF and placard.
(2)
Open APU compartment access door latches and open access door. Install door support rods.
(3)
Support lower shroud, open shroud latches, and remove shroud.
CAUTION: EXERCISE EXTREME CARE NOT TO DAMAGE SHROUD DRAIN LINES WHEN HANDLING SHROUD.
D. Check APU Fuel System
(1)
Disconnect fuel hose from inlet side of low-pressure fuel filter assembly.
(2)
Remove elbow fitting from inlet side of filter head. Remove and discard packing. Save fitting for installation on filter assembly.
(3)
Install a bulkhead tee fitting in inlet port of filter head.
(4)
Connect fuel hose to one side of the bulkhead tee fitting.
(5)
Connect suitable hose and pressure gage to the other side of the bulkhead tee fitting.
(6)
Remove placard and position BATTERY SWITCH to ON.
(7)
Open APU fuel valve by positioning APU MASTER SWITCH to ON.
(8)
Connect external AC power to airplane.
(9)
Position either the forward or aft No. 1 tank AC boost pump to ON.
(10)
Observe boost pressure (approximately 20 psig) on pressure gage.
(11)
Close APU fuel valve by positioning APU MASTER SWITCH to OFF and placard.
(12)
Position No. 1 tank AC boost pump switch to OFF.
(13)
Observe fuel pressure at pressure gage:
(a)
There should be no decay in pressure.
(b)
Correct any leaks in the system which are causing pressure decay (APU fuel solenoid valve, check valve, etc.).
(14)
Bleed off fuel pressure by loosening "B" nut at hose.
(15)
Disconnect hose and pressure gage from bulkhead tee fitting.
(16)
Disconnect fuel hose from other side of the bulkhead tee fittings.
(17)
Remove bulkhead tee fitting from inlet port of filter head.
(18)
Install elbow fitting with packing in inlet port of filter head.
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