L20379H28211
Engine Fire Extinguishing System Component Location 553
26-21-0 Figure 1 May 01/01
Page 2
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
500 Engine Fire Extinguishing System Circuit
Feb 15/68 Figure 2 26-21-0
Page 3
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
2. Fire Protection System Module Components
A. The fire protection system module components described in the following paragraphs will be only those associated with the engine fire extinguishing system. The fire protection system module (P8-l) is located on the aft electronic panel (P8). For further information on the fire protection system module, refer to 26-00, Fire Protection.
B. Fire Switch
(1)
The fire switch is a combination seven-pole, double-throw, push-pull and a four-pole single- throw rotary switch with a holding solenoid and lighted handle (See Figure 2). Two poles of the rotary switch are actuated by clockwise rotation of the handle and the other two poles are actuated by counterclockwise rotation of the handle. The handle is spring-loaded to the normal position. The solenoid is provided with a mechanical override to be used in event of a malfunction.
(2)
The engine fire switches give a visual indication of a fire warning for their associated engine. The fire warning signal will also actuate the solenoid in the fire switch for the associated engine. Actuation of the solenoid will permit the shaft and handle to be pulled. When the fire condition is confirmed the applicable fire switch is pulled to shut off the flow of engine bleed air, inflammable fluids and electrical power to and from the fire zone and arm the fire extinguishing system for subsequent action.
C. Bottle Discharge Light
(1)
An amber bottle discharge light is provided to indicate that the associated bottle has been bled off. When either the left or right bottle has been discharged or the safety relief valve has melted and bottle pressure is bled off, the associated bottle discharge light will illuminate.
(2)
The warning lights may be tested individually by a press-to-test feature in the light assembly or the lights may all be tested simultaneously when the master test switch is closed.
500
26-21-0 Page 4 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. Nov 15/66
D. Test Switch
(1)
A three-pole, double-throw, pushbutton switch is provided to permit testing of the fire extinguishing system through a test circuit connected to the bottle discharge squib and selector control valves. The system may be tested either while the airplane is in flight or on the ground.
(2)
The fire extinguisher test circuit provides the means to check the bottle discharge squib for continuity without actually discharging the squib and checks control valve continuity.
(3)
Pressing the EXT TEST switch sends a very small current through each bottle discharge squib. Each selector control valve is in series with the associated test light ground. If the circuits are complete, a transistor in each circuit is biased. The biased transistors will conduct a signal to illuminate the associated extinguisher test lights. The extinguisher test lights are green press-to-test lights located on the face of the fire protection system module (P8-l).
3. Fire Extinguisher Bottle Assemblies
A. The two fire extinguisher bottle assemblies each consist of a spherical steel container fitted with a filling port plug which contains a red safety release indicator, a pressure switch metal sealing disk in the discharge port and a discharge plug which contains a yellow primary release indicator. Each spherical steel container is about 8-1/2 inches in diameter and has a volume of approximately 224 cubic inches. The bottles are used to store the extinguishing agent under pressure until released by fire extinguishing discharge action. Each bottle is filled with 3.5 pounds of freon, and charged with dry nitrogen.
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