(d)
Do a check of the bonding resistance between the fuel tube(s) and the airplane structure (SWPM 20-20-00).
NOTE: The resistance must not be more than 0.010 ohm.
____
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747-400 MAINTENANCE MANUAL
G. Do a Leak Check for the Fuel Line in the Strut Area
NOTE: The purpose of this check is to make sure the fuel line in
____ the strut area is installed correctly. Use one or both methods to leak check the fuel line in the strut area. A fuel pressure leak check is the preferred method, however, it is recommended that both an air pressure leak check and a fuel pressure leak check be done. If METHOD 1 is done first, it will reduce the possibility of a fuel leak and the possible time delay caused by the removal of fuel from the fuel line if maintenance action is necessary to repair a leak.
METHOD 1:
Air Pressure Leak Check. This method uses 40 psi air pressure
with the fuel spar valve closed to check the fuel line in the
strut area for leaks.
METHOD 2:
Fuel Pressure Leak Check. This method uses a visual inspection of
the fuel line in the strut area with the fuel spar valve open and
the fuel line pressurized with fuel from the fuel tank pumps.
S 784-089
(1) METHOD 1;
Air Pressure Leak Check.
NOTE: Use one of these equipment set-ups:
____ -G28018 air pressure equipment or,
-Air pressure check equipment set-up at the engine fuel pump (Fig. 403).
(a)
If available, install the G28018 equipment at the fuel quick-disconnect (service disconnect panel). 1) Connect the G28018 pressure check equipment to the air
pressure source.
(b)
To install the air pressure check equipment set-up at the applicable engine fuel pump, do these steps (AMM 73-11-01/401). 1) Remove the bolts and washers which hold the hose and the
bracket to the engine fuel pump. 2) Disconnect the hose for the fuel pump. 3) Remove the gasket. 4) If the gasket has no damage, keep it for the installation. 5) Install a cap on the open end of the fuel hose. 6) Connect the pressure check equipment to the air pressure
source and the flange on the airplane fuel supply tube on the applicable engine (Fig. 406).
(c)
Use the air pressure source to apply 40 psig pressure to the fuel line from the airplane fuel supply tube to the fuel spar valve.
(d)
Close the shutoff valve on the pressure check equipment.
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MAINTENANCE MANUAL
(e) Monitor the pressure gage for 10 minutes.
1) If the pressure stays the same or the pressure decreases by less than 1.5 psi in 10 minutes, the fuel line is satisfactory. a) If the fuel line is satisfactory, remove the pressure
check equipment.
2) If the pressure decreases more than 1.5 psi in 10 minutes, there is a leak in the fuel line. a) If there is a leak, do the subsequent steps.
(f) Do a check for air leaks.
1) Use the air pressure source to apply 40 psig pressure to the fuel line from the airplane fuel supply tube to the fuel spar valve.
2) Close the shutoff valve on the pressure equipment.
3) Listen for air leaks in the fuel line.
4) When you find the leak, remove the air pressure from the
fuel line.
CAUTION: YOU CANNOT TIGHTEN THE FUEL LINE COUPLING AFTER THE
_______ INITIAL INSTALLATION. YOU MUST INSTALL A NEW O-RING WHEN YOU TIGHTEN THE FUEL LINE COUPLING OR A FUEL LEAK CAN OCCUR.
5) If a coupling has a leak, disconnect the coupling, replace the O-rings, and then connect the coupling again (AMM 28-00-00/201). a) Make sure the O-ring(s) are lubricated with the
petrolatum. 6) If a fuel tube has a leak, replace the fuel tube. 7) After you have repaired the leak, remove the air pressure
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