*
Two cap rests
*
Inlet port
*
Diaphragm
*
Two squibs
*
Outlet port
*
Debris screen.
Location
The two flow valves are behind the right sidewall lining of the forward cargo compartment, near the ceiling. The forward flow valve is above the metered bottles. The aft flow valve is above the dump bottles. Access is through the fire bottle access panels.
Functional Description
The inlet port connects to the fire extinguishing bottles. The outlet port connects to the discharge line. The valve is normally closed by the diaphragm between the inlet and outlet.
Two explosive squibs are adjacent to the diaphragm. The squibs fire when you operate the related fire extinguishing controls. The explosion tears the diaphragm and lets halon go through the valve. The debris screen catches pieces of the disc and squibs to prevent contamination of downstream components. Only one squib is necessary to tear the diaphragm. Two squibs are used to make sure the valve opens.
Training Information Point
Replace the correct flow valve after the fire extinguishing system operates. Different size inlet and outlet ports prevent incorrect installation. The two squibs have the same purpose. Connect the airplane wiring to the squibs in any sequence. The forward and aft flow valves are interchangeable.
WARNING: INSTALL THE PROTECTIVE CAPS ON THE ELECTRICAL CONNECTORS ANY TIME THE AIRPLANE WIRING IS NOT CONNECTED. ACCIDENTAL DISCHARGE OF THE SQUIBS CAN CAUSE INJURY.
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LOWER CARGO FIRE EXTINGUISHING -FLOW VALVE
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LOWER CARGO FIRE EXTINGUISHING -FLOW VALVE SQUIB
Purpose
The squibs open the flow valve to let halon go to the forward or aft cargo compartment.
Location
The squibs are in the flow valves.
Physical Description
The squib is an electrically operated explosive device. It is adjacent to a diaphragm that can break. The diaphragm normally isolates the valve inlet from the outlet.
Functional Description
The squibs fire at the same time the dump bottles discharge. The explosion opens the diaphragm. Halon flows through the flow valve to the discharge nozzles.
Training Information Point
WARNING: DO NOT TOUCH THE SQUIB BEFORE YOU DO THE PROCEDURES FOR DEVICES THAT ARE SENSITIVE TO ELECTROSTATIC DISCHARGE. ELECTROSTATIC DISCHARGE CAN CAUSE THE SQUIB TO FIRE AND CAUSE INJURY TO PERSONS.
WARNING: PUT A PROTECTIVE COVER ON THE SQUIB. IF YOU DO NOT PUT A PROTECTIVE COVER ON THE SQUIB, THE SQUIB CAN ACCIDENTLY FIRE AND CAUSE INJURY TO PERSONS.
You must replace the squib every 10 years. The service date is on the squib. Both flow valve squibs are the same. Connect the airplane wiring to the squibs in any sequence.
The lower cargo extinguishing system does a test of the squibs during each flight leg. Look at the status messages, maintenance messages or the fire protection maintenance page to see if the squibs are serviceable. You can also use the MAT to do a test of the squibs.
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LOWER CARGO FIRE EXTINGUISHING -FLOW VALVE SQUIB
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LOWER CARGO FIRE EXTINGUISHING -FUNCTIONAL DESCRIPTION -FLOW
General
An explosive squib inside the discharge assembly releases halon from the bottles. Flow valves, also operated by explosive squibs, let the halon go to the forward or aft cargo compartment. Flight and ground operation are different.
Operation -Flight
This is what happens when you operate the controls for a lower cargo fire:
*
The squibs for bottles 1A and 1B fire
*
The squibs in the selected flow valve fire
*
A twenty-minute timer in the ELMS starts.
The squib explosion opens the diaphragms in the dump bottles and in the selected flow valve. Nitrogen pressure pushes the halon from the bottles, through the open flow valve, and into the selected cargo compartment. Pressure in the discharge line operates the in-line pressure switch. This switch gives a flight deck indication of bottle discharge.
Pressure switches monitor the pressure in the dump bottles. When the pressure decreases, the switches causes low pressure indications to show in the flight deck.
After twenty minutes, the ELMS fires the squibs for bottles 2A, 2B, and 2C. Halon from the bottles goes through the filter/ regulator and into the selected cargo compartment. The filter/ regulator causes a slow and continuous flow of halon into the cargo compartment to keep the fire out.
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