5.  Filter/Drier
____________
 A.  The filter/driers are located on the ceiling of the right side in the forward cargo compartments and in the aft cargo compartment. After the extinguishing agent is discharged from cargo bottles, the filter/drier filters water from extinguishing agent to prevent the outlet nozzle from freezing. Filter/drier must be replaced after use (AMM 26-23-04/401).
 6.  Regulators
__________
 A.  The regulators are located in the ceiling on the right side in the forward cargo compartment and in the aft cargo compartment. After the extinguishing agent passes through the filter/driers, the extinguishing agent passes through regulators which maintains a constant level of pressure discharging agent for 180 minutes (AMM 26-23-03/401).
 7.  Operation (Fig. 2)
_________
 A.  Functional Description
 (1)  
When a fire is detected in a lower cargo compartment (forward, aft, and bulk), the appropriate lights (FWD or AFT) on the fire control module illuminate.

 (2)  
The discharge circuit for the appropriate lower cargo compartment is armed by pressing ARMED switch on the fire control module. A white light in the switch will come on to verify the extinguisher bottle is armed. When the FWD ARMED switch is pressed, the following are turned off:

 (a)  
All upper and lower air conditioning recirculation fans

 (b)  
Lav fan.

 (c)  
Cooling for electrical equipment goes to override shutting off the forward cargo heat system

 (d)  
Air conditioning pack number 3 shuts off automatically. One of the remaining two air conditioning packs will be shut off by the flight crew. The remaining air conditioning pack goes into high flow mode.

 (e)  
Forward overboard valve closes

 (3)  
When the AFT ARMED switch is pressed, the following are turned off:

 (a)  
All upper and lower air conditioning recirculation fans

 (b)  
Bulk cargo vent fan

 (c)  
Air conditioning pack number 3 shuts off automatically. One of the remaining two air conditioning packs will be shut off by the flight crew. The remaining air conditioning pack goes into high flow mode.

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747-400
MAINTENANCE MANUAL

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747-400 MAINTENANCE MANUAL
M7353 EIU M7352 EIU M7351 EIU

Lower Cargo Compartment Fire Extinguishing System Simplified Schematic Figure 2 (Sheet 2)
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747-400 MAINTENANCE MANUAL
 (d)  
Cooling for electrical equipment goes to override shutting off the aft cargo heat system

 (e)  
Forward overboard valve opens

 (4)  
To discharge the extinguisher bottles into the selected compartment, press BTL DISCH switch on fire control module. The electrical signal from the bottle discharge switch detonates the squib cartridge, rupturing the retaining discs on each bottle, and releasing the extinguishing agent.

 (5)  
The first two fire bottles are discharged to flood the lower cargo compartment to five percent concentration. The third and fourth bottles are discharged thirty minutes later by using the time delay in the relay. The concentration of the extinguishing agent is maintained approximately three percent for 150 minutes. The total discharging time is 180 minutes.
　
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