(2)
Perform steps 2.B.(1) thru 2.B.(9).
(3)
Position APU BLEED AIR switch to CLOSE (allow duct pressure to stabilize at zero).
(4)
Position APU BLEED AIR switch to OPEN.
(5)
Measure time from actuation of APU BLEED VALVE switch to stabilize minimum frequency reading. This should occur within 12 to 14 seconds.
NOTE: APU bleed air (load control) valve opening should occur 12 to 14 seconds from time APU bleed air valve switch is actuated till time frequency meter indicates minimum frequency.
In addition, the duct pressure indicator will show minimum duct pressure, indicating that the bleed air (load control) valve has reached full open position.
(6)
Position air conditioning R PACK and L PACK valve switches to OFF.
(7)
Position APU BLEED AIR switch to CLOSE.
(8)
Allow engine to operate at "no load" governed frequency for one minute minimum.
(9)
Position APU master switch to OFF.
(10)
If time in step (5) was not met, adjust bleed air valve rate control adjustment screw as follows:
(a)
Make sure BATTERY switch is OFF and placard.
(b)
Open APU compartment access door latches and open access door. Install door support rods.
(c)
Support shroud, open shroud latches, and remove shroud.
CAUTION: EXERCISE EXTREME CARE NOT TO DAMAGE SHROUD DRAIN LINES WHEN HANDLING SHROUD.
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(d) Adjust bleed air valve rate control adjustment screw as follows (Fig. 502): 1) Loosen jamnut on rate control adjustment screw. 2) Turn adjustment screw clockwise to increase opening time or counterclockwise
to decrease opening time. 3) Tighten jamnut on adjustment screw. 4) Repeat steps (2) thru (9) and (10)d) [1) thru 3)] until valve is adjusted correctly.
(11) Restore airplane to normal configuration.
(a)
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.
(b)
Disengage APU compartment access door support rods and stow rods. Close latch access door.
(c)
Remove placard from BATTERY switch.
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G02916
589 Bleed Air Valve Adjustments
Aug 15/80 Figure 502 49-11-0
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AUXILIARY POWER UNIT - INSPECTION/CHECK
1. General
A. The APU inspection/check consists of checks of the APU as a whole, as well as examinations and checks of certain engine and engine system components. These components are accessible directly or with minimum parts removal such as removal of shroud doors or exhaust duct. If distress is found when performing checks 3.A.(2), and 3.A.(3) the distress may be indicative of critical engine condition, and detailed examination of APU should be considered.
B. APU condition monitoring consists of a periodic check of those critical parameters of APU operation, which indicate the condition of the APU.
2. Materials and Equipment
A. Fiber Optics (Borescope)
3. Examine Auxiliary Power Unit
A. Check engine for the following:
(1)
Compressor air inlet for loose fasteners.
(2)
Combustion chamber liner assembly for damage. Remove combustor unit (Ref 49-31-42). Examine per Fig. 601.
(3)
Examine critical engine condition for damage as follows (Fig. 601):
NOTE: If cracks, erosion, deformation or other obvious damage is greater than the limits in Fig. 601, remove APU for hot section inspection. Instructions for performing HSI are outlined in Heavy Maintenance Section of the APU Engine Overhaul Manual, 49-20-31.
(a)
Remove exhaust duct muffler (Ref 49-80-11, R/I).
(b)
Visually check that oil tank vent hose ID and opening in fitting are not obstructed.
(c)
Visually examine exhaust flange assembly for cracks.
(d)
Visually examine turbine plenum assembly for cracks in welds and adjoining material.
(e)
Visually examine turbine wheel and exducer for cracks, rubbing, blade tip bending and thinning due to erosion.
(f)
Check turbine plenum gasket for evidence of deterioration and leakage.
(g)
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