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C.  The main distribution manifold is located aft of the forward cargo compartment aft bulkhead in a pressurized area (Fig. 1).
2.  Main Distribution Manifold Relief Valve (Not on all Airplanes)
A.  The main distribution manifold relief valve begins to open at approximately 17 inches of water and limits pressure in the manifold to approximately 27 inches of water. This relief valve protects the manifold and all the conditioned air ducts from excessive pressure surges.
B.  The relief valve is located in the duct section extending from the ground service conditioned air connector to the manifold (Fig. 1). An opening in the duct is covered by a flapper-type plate which is spring-loaded closed. Two adjustable springs hold the plate closed unless duct pressure exceeds 17 inches of water.
503 
Feb 20/85  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  21-21-0 Page 1 

 

G93939 E62192
Main Distribution Manifold  535 
21-21-0  Figure 1 (Sheet 1)  Feb 20/85 
Page 2 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

536  Main Distribution Manifold 
Feb 20/85  Figure  1 (Sheet 2)  21-21-0 
Page 3 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

3.  Ground Service Conditioned Air Connection
A.  A ground service connection is provided to allow use of a ground service cart for conditioned air to the cabin when airplane air conditioning is off. A check valve in the duct prevents loss of air when airplane air conditioning is on.
B.  The connection is a short duct section, which is fastened to the pressure skin, and the duct and check valve assembly at its upper flange and has three slotted holes in its lower flange to match fasteners on the ground service cart. (See figure 1.) An access door must be opened to make the connection.
C.  A swing check valve in the duct and check valve assembly opens with pressure from the ground service cart and closes when air is being supplied from the airplane air conditioning system.
525 
21-21-0 Page 4  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  Dec 15/70 

GROUND SERVICE CONDITIONED AIR CONNECTION DUCT AND CHECK
VALVE ASSEMBLY - REMOVAL/INSTALLATION

1.  General
A.  The duct and check valve assembly hinge is spring-loaded to hold the swing check valve slightly open when air conditioning is off. When air conditioning is on the pressure in the distribution ducts is enough to overcome the spring-load and cause the check valve to close. Before installation of a duct and check valve assembly the check valve should be checked and the hinge adjusted, if required, to obtain the open or closed position.
2.  Equipment and Materials
A.  Primer - RTV 1200, Dow Corning, or equivalent
B.  Adhesive - 30-121, Dow Corning, or equivalent
C.  Solvent – Final Cleaning of Metal Prior to Non-structural Bonding (Series 88)
(Ref. AMM/SOPM 20-30-88)

3.  Remove Duct and Check Valve Assembly
A.  Remove center portion of forward cargo compartment aft bulkhead to gain access to air conditioning distribution bay.
B.  Remove band clamps and disconnect flexible duct from duct and check valve assembly.  (Fig. 401)
C.  Remove bolts and washers from lower flange of duct and check valve assembly.
D.  Remove duct and check valve assembly.
503 
May 01/98  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  21-21-11 Page 401 

Duct and Check Valve Assembly  505 
21-21-11  Figure 401 (Sheet 1)  Feb 20/85 
Page 402 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

E63143
503  Duct and Check Valve Assembly 
Feb 15/71  Figure 401 (Sheet 2)  21-21-11 
Page 403 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

4.  Prepare Duct and Check Valve for Installation
A.  Check that gasket bonded to pan is not damaged. If damaged, replace.
(1)  
Remove gasket.

(a)  Remove gasket and old adhesive with putty knife or similar tool with a medium sharp edge. Clean the remaining adhesive with solvent, Series 88 (Ref AMM/SOPM 20-30-88).

(2)  
Install gasket.

(a)  
Brush a coat of RTV 1200 primer on bonding surface except the silicone rubber gasket.

CAUTION: DO NOT USE IF THE PRIMER TURNS CLOUDY OR MILKY.
　
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