S 434-017

 (10)
 Install the clamp to hold the flexible duct to the check valve.

 (a)  Tighten the clamp nuts to 40 - 50 pound-inches
 (4.52 - 5.64 newton-meters.
 D. Do the Installation Test for the Check Valve
 S 864-025
 (1)  
Remove the DO-NOT-OPERATE tag from the applicable PACKS selector, on the P5 panel.

 S 864-019

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

 S 794-020

 (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 414-021
 (1)  
Close the applicable access door or panel, 191F-L, 191N-L, 192F-R (Ref 06-09-03/201).

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

 S 864-024
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A
747-400 MAINTENANCE MANUAL
 COOLING AIR CHECK VALVE - INSPECTION/CHECK
__________________________________________
 1.  General
_______
 A.  This procedure has instructions to do an inspection of the cooling air check valves. One check valve is installed in each ram-air inlet duct.
 TASK 21-51-14-206-001
 2.  Cooling Air Check Valve Inspection
__________________________________
 A.  References
 (1)  
21-51-14/401, Cooling Air Check Valve

 (2)  
IPC 21-62-56 Fig. 1 and 2

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

 (2)  
Access Panels
 191F-L Air Conditioning Access Panel
 191N-L Air Conditioning Access Door
 192F-L Air Conditioning Access Panel

 C.  Do the Inspection
 S 026-002
 (1)
Do the Cooling Air Check Valve Removal (Ref 21-51-14/401).

 S 216-008

 (2)  
Make sure these conditions occur on the check valve.

 (a)  
There is no corrosion or other damage to the check valve.

 (b)  
The check valve does not have a crack.

 (c)  
The flappers in the check valve are not bent, broken, or loose.

 (d)  
The flappers move easily. 1) Push each flapper to the fully open position. 2) Release the flapper. 3) Make sure the flapper moves easily to the closed position.

 NOTE: If the pin is worn or the spring is broken, the
____ flapper will not close.
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A 747-400 MAINTENANCE MANUAL
 (3)  S 966-006If one of the conditions did not occur, replace the check valve.
 (4)  S 426-007Do the Cooling Air Check Valve Installation (Ref 21-51-14/401).

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400 MAINTENANCE MANUAL
 RAM-AIR SCREEN - REMOVAL/INSTALLATION
_____________________________________
 1.  General_______
 A.  This procedure has instructions to remove and install the ram-air screens. One screen is attached to each fan diffuser and inlet housing. You must remove the fan diffuser and inlet housing before you can isolate the ram-air screen.
 TASK 21-51-15-004-001
 2.  Ram-Air Screen Removal (Fig. 401)______________________
　
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