747-400
MAINTENANCE MANUAL

COMPRESSOR BYPASS CHECK VALVE (3 PLACES)
FWD 
SEE  A 
SEE  A 
EQUIPMENT BAY AIR CONDITIONING SEE  A  (2 PLACES) COUPLING  DUCT 
(2 PLACES) COUPLING 
SEE  B 
DUCT  SEAL ASSEMBLY (2 PLACES) B 

CHECK VALVE
AFT A
Compressor Bypass Check Valve Installation Figure 401
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 ALL  ú ú 01 Page 402 ú Jun 10/88
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400 MAINTENANCE MANUAL
 S 034-005
 CAUTION:_______DO NOT TOUCH THE PACK DUCTS WHEN THEY ARE HOT. IF THE PACK WAS ON, THE DUCTS CAN BE HOT AND CAN CAUSE INJURY TO PERSONS.
 (1)  
Remove the couplings from each end of the check valve.

 S 024-006

 (2)  
Remove the check valve.

 S 284-020

 (3)  
Do a detailed visual inspection of the check valve. If you find any of the following conditions, then replace the check valve.

 (a)  
missing or worn components

 (b)  
cracks, corrosion, or damage

 (c)  
flappers do not operate freely

 TASK 21-51-06-404-008
 3.  Compressor Bypass Check Valve Installation (Fig. 401)__________________________________________
 A. References
 (1)  
06-09-03/201, Body Section 44 Access Doors and Panels

 (2)  
21-00-00/201 Air Conditioning

 (3)  
IPC 21-51-06 Fig. 1

 B. Access
 (1)  
Location Zone
 133 Air Conditioning Equipment Bay, LH
 134 Air Conditioning Equipment Bay, RH

 (2)  
Access Panel
 191A-L Air Conditioning Access Door
 191H-L Air Conditioning Access Door
 192A-R Air Conditioning Access Door

 C. Install the Check Valve
 S 964-017
 CAUTION:_______DO NOT TOUCH THE PACK DUCTS WHEN THEY ARE HOT. IF THE PACK WAS ON, THE DUCTS CAN BE HOT AND CAN CAUSE INJURY TO PERSONS.
 (1)  
If the seals in the duct flanges are damaged, worn, or have a crack, then replace the seals.

 (2)
Put the check valve in its position in the air cooling pack.

 S 024-010
 NOTE: Make sure the flow arrow on the check valve points aft.
____ The check valve flanges are different diameters to make sure you do not install the check valve in the incorrect direction.
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 ALL  ú ú 01 Page 403 ú Oct 18/01
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400 MAINTENANCE MANUAL
 S 034-011
 (3) Install the couplings on each end of the check valve.
 (a)  Tighten the coupling nuts to 65 - 75 pound-inches
 (7.35 - 8.47 newton-meters).
 D. Do the Installation Test for the Check Valve
 S 864-018
 (1)  
Remove the DO-NOT-OPERATE tag from the applicable PACKS selector, on the P5 panel.

 S 864-012

 (2)  
Operate the applicable air cooling pack (Ref 21-00-00/201).

 S 794-016

 (3)  
Feel for leaks around the check valve.

 (a)  
Small leaks are permitted.

 (b)  
You must repair a large leak.

 E. Put the airplane to its usual condition
 S 414-014
 (1)  
Close the applicable access door, 191A-L, 191H-L, 192A-R
 (Ref 06-09-03/201).

 S 864-015

 (2)
Do the procedure to stop the air cooling pack (Ref 21-00-00/201).

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