D. The pressure gage indicates pressure in the extinguisher bottle. The gage also contains a pressure switch that will close and activate the bottle discharge lights when the bottles are discharged or pressure drops. The pressure gages are visible on the left side of the main wheel well.
E. The discharge port is sealed by a frangible restraining diaphragm to retain the pressurized extinguishing agent. The discharge plug is installed at the discharge port and serves as an adapter between the bottle and manifold, and provides the means to discharge the bottle. When the squib receives a signal from the applicable fire switch, it is detonated (Fig. 2). The detonation creates a shock wave which ruptures the diaphragm allowing the extinguishing agent to escape.
NOTE: The fire extinguisher bottles are not designed for recharging while installed in the airplane. A low pressure or discharge bottle should be replaced with a charged bottle.
F. A manifold connecting the two bottles includes a tee fitting or a double check valve. The check valve (if installed), prevents extinguishing agent from entering a discharged bottle. A tee fitting in the manifold connects each engine selector valve with both extinguisher bottles.
4. Selector Control Valves
A. Two selector control valves are provided, one for each engine (Fig. 1). Each valve is solenoid controlled by the applicable fire switch handle (Fig. 2). The valves are mounted on the aft bulkhead in the left wheel well on the outboard side.
B. Each selector valve is solenoid controlled, pressure actuated. When the fire switch handle is turned, the squib is detonated and the solenoid energized, directing the bottle pressurized gas to a pilot valve in the control valve. The pressurized gas opens the pilot valve and directs the extinguishing agent into the applicable discharge line.
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5. Discharge Lines
A. The discharge lines disperse the released extinguishing agent from the selector valves to the selected fire area. The lines to each engine are routed along the rear spar and forward along the top of the engine to approximately the center or the engine. Nozzles disperse the extinguishing agent around the engine at a proper rate for effective extinguishing.
6. Operation
A. When a fire warning indication is received, the associated fire switch handle will be unlocked. When it is determined a fire condition exists and corrective action must be taken, pull up on the fire switch handle. When the handle is pulled up the fire extinguisher system is armed, and the cam is moved into position to actuate the associated control valve and discharge squib. Besides arming the fire extinguisher system, the engine fire switches perform the following functions:
(1)
Closes fuel shutoff valve on affected engine.
(2)
Closes hydraulic fluid shutoff valve.
NOTE: When the hydraulic fluid shutoff valve is closed the associated low pressure lights are bypassed to prevent a false low pressure warning.
(3)
Closes air bleed valve.
(4)
Deleted
(5)
Trips the generator control relay for affected engine. The relay de-energizes the generator field and disconnects the generator from the ac bus within 5 to 10 seconds.
NOTE: For additional information on engine shutdown, refer to Chapter 76, Engine Fire Emergency Shutdown.
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B. When the system is armed the fire switch handle may be rotated to the left or right to discharge the left or right bottle respectively. When the handle is rotated to the right (for at least one second), the engine selector control valve solenoid is energized and the squib on the right bottle is fired, rupturing the sealing diaphragm and releasing the extinguishing agent. The extinguishing agent flows through the double-action check valve into the manifold. The energized engine selector valve directs pressurized gas to the pilot valve section of the control valve. The pilot valve opens the main valve and allows the extinguishing agent to discharge into the engine. The main valve of the selector valve will remain open until the discharge pressure drops to 25 pounds per square inch (Fig. 2). When the bottle pressure approaches approximately 250 psi, the right bottle discharge light illuminates, indicating the right bottle is discharged and inactive.
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