Piper Navajo PA-31 Service Manual page 602

9-13e. DEFECT REPAIRS OF FUEL CELL.
a. Blisters: Remove loose material by trimming. Apply an outside and inside repair patch.
b. Holes, Punctures, Cuts, Tears and Deep Abraded Areas: Trim away any ragged material and apply an
outside and inside repair patch.
c. Loose Seams: Buff loose edge and contact surface with emery cloth. Wash three times with Methyl
Ethyl Ketone. Apply 80C27 mixed cement two coats as with repair patch. Clamp and cure. Either method may
be used. See repair patch. Loose seams may be trimmed if minimum lap remains.d. Loose Fitting Flange
- Inside: Buff edge of flange and contact surface under flange. Apply 30C27 mixed repair cement, cellophane,
padded plates and clamp. Follow procedure as outlined for repair patch, except for patch itself.
e. Looseness Against Metal: Prepare metal as per metal fitting - sealing surfaces. Apply 80C27 mixed
cement and cure.
9-14.
TESTING FUEL CELLS. Either of the following test procedures may be used to detect leaks in the
bladder cells.
a. Soap Suds Test.
1. Attach test plates to all fittings.
2. Inflate the cell with air to a pressure of 1/4 psi MAXIMUM.
3. Apply a soap and water solution to all repaired areas and any areas suspected of leakage. Bubbles
will appear at any point where leakage occurs.
4. After test, remove all plates and wipe soap residue from the exterior of the cell.
b. Chemical Test.
1. Attach test plates to all fitting openings except one.
2. Make up a phenolphthalein solution as follows: Add 40 grams phenolphthalein crystals in 1/2 gallon
of Ethyl Alcohol, mix, then add 1/2 gallon of water.
3. Pour ammonia on an absorbent cloth in the ratio of 3ml. per cubic foot of cell capacity. Place the
saturated cloth inside the cell and install remaining test plate.
4. Inflate the cell with air to a pressure of 1/4 psi maximum, cap and maintain pressure for fifteen
minutes.
5. Soak a large white cloth in the phenolphthalein solution, wring it out thoroughly, and spread it
smoothly on the outer surface of the cell. Press the cloth down to insure detection of minute leaks.
6. Check the cloth for red spots which will indicate a leak. Mark any leaks found and move the cloth
to a new location. Repeat this procedure until the entire exterior surface of the cell has been covered. If red
spots appear on the cloth, they may be removed by resoaking the cloth in the solution.
7. The solution and test cloth are satistactory only as long as they remain clean. Indicator solution
that is not in immediate use should be stored in a closed rust proof container to prevent evaporation and
deterioration.
After the test, remove all plates and test equipment. Allow the cell to air out.
In conducting either test outlines above, the cell need not be confined by a cage or jig, providing the
1/4 psi pressure is not exceeded.
NOTE
The chemical test is the more sensitive and preferred test.
9-14a. LOCKING FUEL CAP (Optional). On aircraft S/N 31-8212001 and up, an optional Shaw Aero locking
gas cap is available for each fuel cell.
Revised: 2/18/94
FUEL SYSTEM
3B10
PIPER NAVAJO SERVICE MANUAL