(2)
Toluene TT-T-548 or JAN-T-171 Grade A
B. Tapes (Ref 20-30-51)
(1) HT1-41 Nomex tape, 4 inches wide
C. Adhesives (Ref 20-30-11)
(1)
GE RTV 133 or
(2)
BMS 5-7 Type II or
NOTE: 3M P/N EC-4419 is recommended, but P/N EC-2155 may be used until existing stock is depleted.
(3)
GE PSA-529/SRC-18
3. Remove Aft Overhead Distribution Duct
A. Remove ceiling panel.
B. Remove screws holding duct to ceiling supports.
C. Disconnect forward end of duct from overhead duct.
(1)
Insert a protective sheet metal guard between the top of the duct and the ceiling insulation to protect the insulation when cutting duct.
(2)
Cut through old tape at the joints between the edges of adjacent ducts.
CAUTION: DO NOT REMOVE OLD TAPE. DUCT JOINT WILL DISINTEGRATE UPON REMOVAL OF THE TAPE.
D. Remove tape connecting aft portion of duct to light fixture.
E. Remove duct section.
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May 01/98 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 21-23-42 Page 401
4. Install Aft Overhead Distribution Duct
A. Telescope end of duct to light fixture inlet as required to allow forward end of assembly to butt against overhead duct.
B. Secure duct to ceiling support.
C. Prepare tape for joining duct sections per one of the following procedures.
NOTE: Retaping over old tape may be made four times at any one joint. If additional taping must be made, cut away taped portion of duct and replace with a short duct section of the same size.
(1)
Use GE RTV 133 adhesive if the color of the adhesive on the initial installation is black.
CAUTION: MAKE SURE THAT YOU USE THE SAME TYPE OF ADHESIVE THAT WAS USED ON THE INITIAL INSTALLATION OF THE DUCT JOINT. THE ADHESIVE WILL NOT BOND TO THE DUCTS UNLESS THE SAME TYPE OF ADHESIVE IS USED.
(2)
Use GE PSA-529/SRC-18 if the color of the adhesive on the initial installation is clear.
(3)
Use BMS 5-7, Type II adhesive if the color of the adhesive on the initial installation is yellow and green.
(4)
Procedure 1 (Ducts without GE RTV 133 adhesive)
WARNING: PREVENT SOLVENT TO SKIN CONTACT; AVOID INHALATION OF VAPORS; USE ONLY IN AREAS WITH ADEQUATE LOCAL EXHAUST VENTILATION.
CAUTION: THIS PROCEDURE DOES NOT APPLY TO DUCTS REPAIRED OR INSTALLED WITH GE RTV 133 BLACK SILICONE ADHESIVE. USE PROCEDURE 2 FOR DUCTS WITH THIS TYPE ADHESIVE.
(a)
Clean faying surfaces of ducts with solvent using dry clean cheesecloth or wipers. Blot dry excess solvent.
(b)
Thin BMS 5-7 Type II adhesive by adding one part of toluene to two parts of adhesive, by volume. Mix thoroughly.
(c)
Install tape joint using one, or a combination of the following three methods. For all three methods the following is applicable: 1) Ensure that there is a minimum of 1.5 inch of fiberglass tape on each duct end. 2) Overlap the tape ends 1-2 inches at the tape joint. Pull out wrinkles in the tape
and smooth out any voids or air pockets between the tape and the ducts.
(d)
Method I: Apply a moderate to heavy coat of adhesive, approximately 0.020-0.030 inch thick to both the tape and to the end of the duct. While the adhesive is still wet, apply the tape to the duct. Apply a liberal topcoat of adhesive to ensure saturation of the tape.
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21-23-42 Page 402 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. Oct 20/92
G42315
502 Overhead Distribution Duct Installation
Oct 20/92 Figure 401 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 21-23-42 Page 403
(e)
Method II: Apply a 3-inch wide coat of thinned adhesive, approximately 0.040-0.060 inch thick to the outside surface of each duct end. While the adhesive is still wet, apply tape to the adhesive coated surface of duct. Apply a liberal topcoat of adhesive to ensure saturation of the tape.
(f)
Method III (For locations with limited access): 1) Place tape on a suitable flexible installation aid. 2) Apply a coat of thinned adhesive approximately 0.040-0.060 inch thick to the
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