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 B.  Air from the left-air-conditioning pack can bypass the mix manifold. This conditioned air flows into the flight-deck-distribution duct and is distributed directly to the flight compartment (Ref 21-22-00).
 C.  Whenever the airplane is parked, the air conditioning packs do not have to be used. Conditioned air can be supplied to the mix manifold through the ground air service connector. The conditioned air can be supplied by any standard air-conditioning ground cart.
 D.  ON GUN 001-004 WITH SB 21-51, AND GUN 005-999; Like the air from the left-air-conditioning pack, air from the ground-air-service connector can bypass the mix manifold and flow directly into the flight-deck-distribution duct.
 2.  Component Details_________________
 A.  Mix Manifold
____________
 (1)  
The mix manifold sits immediately aft of the forward cargo compartment aft bulkhead. Cylindrical in shape with a domed top, the manifold stands about 44 inches high and 24 inches in diameter. The manifold is constructed of thermosetting resin-impregnated aramid fiber fabric.

 (2)  
Three inlet ducts enter the mix manifold's lower section. The inlet ducts allow only tangential airflow into the manifold. Four 8.5 inch diameter outlet ducts exit the manifold from the upper section and channel the airflow to the conditioned air distribution ducts. A spacer between the bottom of the mix manifold and the airplane skin has a hole to drain condensed water from the manifold.

 (3)  
Two aluminum channels called swirl devices mount on the inside of the mix manifold. The 1.25-inch wide channel starts at the bottom of the mix manifold and makes approximately 3/4 of a revolution around the inside to just below the flow straightener. The 2-inch-wide channel starts at a point halfway up the mix manifold and makes approximately 1/3 of a revolution around the inside. The swirl devices spiral upward in a direction opposite to the normal airflow.

 (4)  
A flow straightener completes the manifold's interior. The four-inch-thick aluminum grid mounts below the outlet ducts at the flange between the upper and lower manifold assemblies.

 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú

 21-21-00
 ALL  ú ú 12 Page 1 ú Sep 28/01
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A

757
MAINTENANCE MANUAL

Main Distribution Manifold
Figure 1 (Sheet 1)

EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. GUN 001-004 WITHOUT SB 21-51 ú

 21-21-00
 ú ú 15 Page 2 ú Mar 20/89
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A

757
MAINTENANCE MANUAL

SEE B
TO PASSENGERCOMPARTMENT (2 EACH SIDE)
MIX MANIFOLD
FROM RIGHT AIR CONDITIONING PACK
TO FLIGHT COMPARTMENT
FROM RIGHT RECIRCULATION SYSTEM
FROM LEFT AIR CONDITIONING FROM LEFT
PACK RECIRCULATION SYSTEM FLOW STRAIGHTENER
GROUND AIR 
SERVICE 
CONNECTOR  SWIRL 
LOWER MIX  DEVICES 
MANIFOLD 
B  ASSEMBLY 

Main Distribution Manifold
Figure 1 (Sheet 2)

EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù.
 GUN 001-004 WITH SB 21-51, AND ú 21-21-00
 GUN 005-999  ú
 ú 14 ú BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.  Page 3Mar 20/89 

A

757
MAINTENANCE MANUAL

 (5)  
Air enters the mix manifold tangentially from the inlet ducts. This tangential entrance creates a centrifugal flow within the manifold. The swirl devices inhibit this flow, creating turbulence. The turbulence causes water to separate from the air and collect on the manifold's inner wall. The air continues to spiral up the manifold and enters the flow straightener. The straightener breaks up the swirling motion of the air, and allows an even pressure and volume distribution to each outlet duct.

 (6)  
The water removed at the swirl devices runs down the manifold's inside wall. The water collects at the bottom and is drawn off through the water drain tube and leaves the airplane through a drain port.
　
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