747-400 MAINTENANCE MANUAL
LOWER FORWARD CARGO OVERBOARD EXHAUST STACK
SEE G
STA
770
LOWER FORWARDCARGO EXHAUST CHECK VALVE
LOWER FORWARD CARGO OVERBOARD VALVE
LOWER FORWARD CARGO OVERBOARD BACK-UP VALVE
ELECTRICAL INLET SCREEN CONNECTOR
LOWER FORWARD CARGO OVERBOARD
EXHAUST STACK
G
Ventilation - Component Location Figure 1 (Sheet 7)
D08980
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A
747-400
MAINTENANCE MANUAL
4. Bulk Cargo Flapper Valve
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A. The bulk cargo flapper valves are installed on the compartment left and right sidewalls just forward of the aft bulkhead. A solenoid, which is mounted above the flapper valve, holds the valves in the normally open position. When open the valves provide an outlet for air discharged into the compartment by the aft cargo conditioned air system. The valves close to isolate the cargo compartment when the compartment fire suppresion sytem is discharged.
5. Forward Cargo Ventilation Fans
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A. The forward cargo vent fans are single stage vaneaxial fans installed in the ceiling area of the forward cargo compartment. The fans are installed on the left hand side at Sta 660 and 900. The fans are powered by 115 volt ac, 400 Hz, three phase power from the 115 vac bus 3.
B. The fan motor has a thermal switch which will open the control circuit in event of excessive temperature in the motor windings.
6. Aft Cargo Ventilation Fan
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A. The aft cargo vent fan is identical to the forward cargo vent fan and is installed behind the compartment sidewall linings at Sta 1740.
7. Bulk Cargo Ventilation Fan
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A. The Bulk cargo ventilation fan is identical to the forward and aft cargo ventilation fans and is installed in the compartment sidewall lining at Sta 2118.
8. Lower Forward Cargo Overboard Exhaust Stack
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A. The lower forward cargo overboard exhaust stack consists of a ground exhaust valve,a back-up ground exhaust valve, and a check valve. The valves are identical 5 inch, motor-operated shutoff valves with limit switches which shut off power in either direction. An override handle, which acts as a position indicator during electrical operation, is provided to allow positioning the valve when power is unavailable or the valve fails.
B. The check valve prevents water from entering the airplane in a ditch condition.
C. The ground exhaust valves are powered by 28 volt dc.
9. Operation
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A. Functional Description - Forward Overboard Valve
(1) The forward overboard valve is controlled by the ECS miscellaneous card. The ECS miscellaneous card utilizes inputs from the CPCS, the pack temperature controllers, an alterate system air/ground relay and an engines on indicator relay for forward overboard valve control logic.
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747-400
MAINTENANCE MANUAL
(2)
With the alternate air/ground relay system in the ground position the forward overboard valve is open. With at least one engine per wing at greater than 50% N2 (i.e. the airplane is configured for takeoff or flight) the engines on indicator relay energizes and the ECS miscellaneous card deenergizes the forward overboard valve relay closing the forward overboard valve.
(3)
During climb, the ECS miscellaneous card will command the forward overboard valve open when a greater than 25,000 feet altitude signal is received from the CPCS and the pack temperature controllers indicate at least two packs are operating.
(4)
During cruise, the forward overboard valve remains open as long as at least two packs are operating.
(5)
When the ECS miscellaneous card receives a decent detect signal from the CPCS the forward overboard valve will close and stay closed until the airplane is on the ground with engines off.
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