(2)
When the airplane is in normal flight with full fuel tanks, the outboard vent ports are open to atmosphere.
RIB
WING TANK
Surge Tank Drain Check Valve
Figure 3
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747-400
MAINTENANCE MANUAL
WING SURGE TANK
FLAME ARRESTER
Surge Tank Vent Flame Arrester
Figure 4
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747-400
MAINTENANCE MANUAL
ACCESS DOOR
WING SURGE TANK
VALVE
A-A
Surge Tank Pressure Relief Valves
Figure 5
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MAINTENANCE MANUAL
(3)
In a wing-low attitude, the inboard vent ports are open and the outboard ports may be covered by fuel. Fuel vent float valves, connected to the outboard ports, prevent fuel from entering the vent system and flowing into the surge tanks. In a wing-high attitude, the outboard ports will be open.
(4)
Fuel entering the inboard ports will drain back into the tank through vent drain valves when the airplane returns to a normal attitude and the fuel quantity drops to below the drain level. Any fuel escaping through the vent system into the surge tanks will drain back into the inboard main tanks through drain line(s) connected to the bottom of each surge tank.
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747-400 MAINTENANCE MANUAL
FUEL VENT DRAIN VALVE - REMOVAL/INSTALLATION
____________________________________________
1. General_______
A. This section supplies instructions for the removal and installation of the drain valve in the fuel vent system.
B. The drain valves are found in all the fuel tanks. They are attached to the vent tubes in the wing tanks. In the center wing tank they are installed on the vent tubes and the hat stringers.
C. A fuel vent drain valve is also installed in each of the surge tanks.
D. The access to the drain valves is through the access doors installed in the wings lower skin. For the center wing tank, the access is through the front spar.
TASK 28-13-01-004-001
2. Remove the Fuel Vent Drain Valve (Fig. 401)________________________________
A. References
(1)
AMM 28-11-00/201, Fuel Tanks
(2)
AMM 28-11-02/401, Reserve and Wing Tank Access Door
(3)
AMM 28-11-03/401,Wing Surge Tank Access Door
(4)
AMM 28-11-09/401, Spanwise Beam Access Door
(5)
AMM 28-26-00/201, Defueling
(6)
AIPC 28-13-01 Fig. 1
B.
Access
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