533 Gasper Fan Circuit Schematic
Feb 15/72 Figure 2 21-24-0
Page 5
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
GASPER AIR DUCT - APPROVED REPAIRS
1. General
A. Cracked or broken polycarbonate (lexan) gasper air ducts are repairable. Two types of repair are used, cementing a patch over the defect, and wrapping tape around the defective area. When properly applied, the patch usually makes a more permanent repair, however, wrapping is usually the faster procedure. The degree of damage considered to be repairable is at the operator’s discretion.
2. Repair by Patching
A. Equipment and Materials
(1)
Sheet material for patch, allowing minimum of 1-inch overlap. Use either:
(a)
Polycarbonate-lexan, approximately 0.020 thickness.
(b)
Aluminum - any thickness and hardness that can readily be shaped to fit damaged area contour.
(2)
Adhesive. Use any adhesive applicable to the specifications listed below (Ref 20-30-11).
(a)
BMS 5-19, Class B
(b)
BMS 5-26, Class B (Proseal 890 only)
(c)
BMS 5-44, Class B (Proseal 890 only)
(d)
BMS 5-79, Class B
(3)
Solvent - Isopropyl alcohol, ethel alcohol or naphtha (Ref 20-30-31)
(4)
Sandpaper - medium grit (commercially available)
B. Repair Duct
(1)
Gain access to damaged section of gasper duct.
(2)
Loosen or remove duct clamps as required, to make duct available for repair.
(3)
Determine area to be repaired and obtain sheet patching material. Trim the damaged area with a sharp knife to provide smooth rounded edges.
(4)
Clean area to be patched.
(a)
If insulation is on duct, remove insulation down to plastic duct.
(b)
Lightly sand areas to be coated with cement to eliminate gloss.
(c)
Clean areas with solvent. Wipe solvent with clean lintless cloth before solvent evaporates.
(5)
Mix adhesive thoroughly and apply uniform brush coat to each faying surface.
(6)
Assemble immediately, applying sufficient pressure to ensure complete contact of faying surfaces. A continuous bead of extruded adhesive usually indicates proper contact.
(7)
Temporarily secure patch with string or tape during initial cure period. Final cure is obtained in a week or more at normal room temperature.
(8)
If insulation was removed from duct in repair area, install section of insulation by using same adhesive.
(9)
Install duct clamps removed above.
(10)
Reinstall items removed to gain access to duct.
500 Severed Duct Joint Repair
May 01/98 Figure 801 21-24-11
Page 801
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
3. Repair by Wrapping
A. Equipment and Materials
(1)
Tape - thermosetting, 1 and 3 inches wide. Fiberglass tape is preferred (Ref 20-30-51)
(2)
Solvent - Isopropyl alcohol, ethel alcohol or naphtha (Ref 20-30-31)
B. Repair Duct
(1)
Gain access to damaged section of gasper duct.
(2)
Loosen or remove clamps as required, to make duct available for repair.
(3)
If crack extends into duct area with insulation, remove insulation from the complete area.
(4)
If duct is severed, remove sharp edges of duct with a file. Areas of cracks in which edges align, thus not exposing a raw edge, do not need filing. If damage is extensive, remove damaged section and install a short section of new duct.
(5)
Clean area to be taped with solvent. Wipe solvent with clean lintless cloth before solvent evaporates.
(6)
Align ducts, if severed, so that gap is 1/8 inch minimum to 3/8 inch maximum and apply tape, using either method:
(a)
Apply two wraps of 3-inch tape, centering tape on joint, smoothing tape to eliminate all wrinkles.
(b)
Apply one wrap of 3-inch tape, centering tape on joint, and overlap tape about 1 inch. Apply a wrap of 1-inch tape around each edge of the 3-inch tape, centering the 1-inch tape on tape edge (Fig. 801).
(7)
On cracked ducts, in which the duct is not severed, apply 3-inch tape to overlap edges and ends of crack 1 inch minimum. Tape may be positioned and overlapped as required, to cover crack.
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