tape. The adhesive will soak through and hold the tape temporarily to the installation aid.
3)  While the adhesive is still wet, position the installation aid against the duct joint with the adhesive side toward the duct. Pull the tape away from the installation aid onto the duct surface. Smooth out any wrinkles and trapped air to ensure that the tape is contacting the duct. If possible, insulation blankets should be prevented from contacting the adhesive to allow air circulation until the adhesive is dry.
(g)  
Allow the GE PSA-529/SRC-18 adhesive to cure under contact pressure for a minimum of 12 hours at 65-100°F before pressurizing the air conditioning system.

(h)  
Allow the BMS 5-7, Type II adhesive to cure under contact pressure for a minimum of 4 hours at 65-100°F before pressurizing the air conditioning system.

(5)  Procedure 2 (ducts using GE RTV 133 adhesive)
(a)  
Coat tape on one side with adhesive. Open time is approximately 30 minutes before a surface skin will begin to form. The tack-free skin interferes with adhesion. Extreme caution must be exercised during application to ensure that no adhesive is applied outside the bond area if subsequent finishing is required.

(b)  
Wrap one layer of coated tape (with adhesive down) over the joint with a minimum of

1.5 inch on each duct. Overlap the tape ends 1-2 inches at the tape joint.

(c)  
Pull out wrinkles in the tape and smooth out any voids or air pockets between the tape and the ducts.

(d)  
Apply positive pressure to ensure contact of the adhesive to the duct. A bondline thickness of 0.04 to 0.08 inches is required. This is approximately 2.0 ounces of adhesive per foot of 4-inch wide tape.

(e)  
Allow the adhesive to cure under contact pressure for a minimum of 24 hours at  65-100°F. A minimum of 20% relative humidity is required for adhesive cure.

D.  Clean area to be taped at ceiling light end of duct with solvent.
E.  Apply two laps of 2-inch vinyl plastic tape to the center of the joint. Pull taut and smooth while applying.
F.  Install ceiling panel.
503 
21-23-42 Page 404  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  Oct 20/92 

FORWARD LIGHT FIXTURE AIR SHUTOFF VALVE - REMOVAL/INSTALLATION
EFFECTIVITY
Passenger/Cargo Convertible Airplanes
1.  General
A.  The air shutoff valve connects the riser duct from the distribution manifold duct assembly to the light fixture. Removal/Installation of the shutoff valve riser ducts at the manifold duct assembly, and the aft overhead distribution duct and valve assembly may use the same procedure.
Equipment and Materials
A.  Cleaning Solvent, BMS 3-2
B.  Vinyl plastic tape, pressure sensitive adhesive, 2 inches wide
3.  Remove Forward Light Fixture Air Shutoff Valve
A.  Remove ceiling panel.
B.  Remove screws holding riser duct and valve assembly to ceiling supports.
C.  Remove tape connecting valve to light fixture.
D.  Remove tape connecting valve to riser duct.
E.  Remove valve assembly.
4.  Install Forward Light Fixture Air Shutoff Valve
A.  Telescope ends of duct to light fixture inlet as required (Fig. 401).
B.  Install screws to hold riser duct and valve assembly to ceiling support.
C.  Clean area to be taped with cleaning solvent.
D.  Apply two laps of 2-inch vinyl plastic tape to the center of the joint, pulling taut and smoothing while applying.
E.  Install ceiling panel.
Nov 15/68 21-23-51 Page 401
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.

Forward Light Fixture Air Shutoff Valve Installation  506 
21-23-51  Figure 401  Nov 15/68 
Page 402 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

VENT MUFFLER - MAINTENANCE PRACTICES
1.  General
A.  Increased noise levels can be caused by increased air velocity through restrictions in the muffler due to contamination or cracks in the muffler shell.
2.  Equipment and Materials
A.  Vinyl tape (Ref 20-30-51)
(1)  Permacel 29
B.  Cylindrical wooden plug
C.  Cleaning Solvent - BMS 3-2 (Ref 20-30-31)
3.  Vent Muffler Cleaning
A.  Remove vent muffler.
NOTE:  Access to muffler, located on LH side opposite galley service door, is gained by removing ceiling panel.
B.  Insert cylindrical wooden plug, slightly less in diameter than muffler flow diameter, through muffler.
C.  If required, repeat procedure through hoses/ducts adjoining muffler.
　
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