The pressure switch monitors the pressure in the container. It has a guard for protection. If the pressure in the container decreases to 200 psi (13.7895 bar) +50 psi (+3.4473 bar) -0 psi (-0.0000 bar) the pressure switch closes and sends a signal to the APU FIRE panel 1WD.
**ON A/C ALL
B. Discharge Outlet (Discharge Head) The discharge head gives a directional flow path for the extinguisher agent. It is installed on the bottle discharge outlet with a coupling nut. Before you tighten the coupling nut you can rotate the discharge head through 360 degrees and thus align it correctly with the distribution pipe. It has a filter to make sure that unwanted material from the fired cartridge and the metal diaphragm do not enter the disrtibution pipe. The distribution pipe connects the discharge head to the discharge outlet in the forward firewall of the APU compartment.
C. Cartridge 12WF The cartridge is installed in the discharge head. It is a high-reliability explosive device and has two squibs (squib A and squib B). When electrical power is supplied to the squibs the cartridge fires and ruptures the metal diaphragm in the bottle discharge outlet. This releases the extinguisher agent.
D. Discharge Indicator The discharge indicator is installed in the fuselage skin between FR78 and FR79. The overboard discharge pipe connects the discharge indicator to the pressure relief device on the fire extinguisher bottle. A red disc is installed in the discharge indicator housing. You can see the red disc if the pressure relief device on the fire extinguisher bottle is in the correct condition. If the pressure relief device operates, the extinguisher agent flows through the overboard discharge pipe to the discharge indicator. The extinguisher agent pressure pushes the red disc out of the discharge indicator housing. This shows that the pressure relief device has operated and that the bottle is no longer serviceable. The red disc is only ejected if the pressure in the bottle is too high. If the cartridge is fired and the agent is released into the APU compartment the red disc stays in the discharge indicator housing.
R 7. Operation/Control and Indicating
________________________________ The APU fire-extinguishing system extinguishes fires in the APU compartment. The system operates when the APU fire and overheat detection system detects an excessive temperature or a fire in the APU compartment (Ref. 26-13-00). The system operates in the subsequent modes:
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APU fire extinguishing in flight,
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APU fire extinguishing on the ground.
The fire extinguisher bottle 11WF also has a pressure relief device which operates if the pressure in the bottle is too high. The pressure relief device can operate in flight or on the ground.
A. APU Fire Extinguishing In Flight (Ref. Fig. 002) In flight the crew must operate the system manually from the APU FIRE panel 20VU in the cockpit. If the FDU 13WG detects an excessive temperature or a fire in the APU compartment it starts the subsequent cockpit warnings: - on the APU FIRE panel 20VU the light in the APU FIRE pushbutton switch
comes on, - on the glareshield panels 130VU and 131VU the MASTER WARN lights flash,
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the Continuous Repetetive Chime (CRC) comes on,
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the ECAM upper display unit shows the message,
APU FIRE
APU FIRE P/B...................PUSH
MASTER SW ......................OFF
LAND ASAP
- on the ECAM lower display unit:
the APU page comes on automatically. When you see the fire warning you must first push the APU FIRE pushbutton switch on the APU FIRE panel 20VU. When you push the APU FIRE pushbutton switch:
-
the 28VDC power supply from the circuit breakers 3WF and 4WF is connected to the fire emergency-stop relays 5WF and 6WF (this energizes the relays),
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the relays 5WF and 6WF connect the power supply from the circuit breakers 1QF and 2QF to the APU low-pressure fuel-shutoff-valve actuator 3QF (Ref. 28-29-00) (the APU low-pressure fuel-shutoff-valve 14QM closes),
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the relay 5WF also sends a signal to the APU Electronic Control Box (ECB) 59KD (Ref. 49-62-00) (the ECB 59KD starts the APU emergency shutdown sequence),
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the 28VDC power supply from the circuit breakers 1WF and 2WF is connected to the AGENT pushbutton switch 10WF (the AGENT pushbutton switch is armed),
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the white SQUIB legend in the AGENT pushbutton switch comes on,
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the FDU 13WG sends a signal to the FWC and the ECAM upper display unit shows the message, APU FIRE AGENT AFT 10 S................DISCH MASTER SW ......................OFF LAND ASAP
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the automatic 10 second countdown starts. After 10 seconds the AFT 10 S indication goes off. (A 10 s delay allows the APU to slow down and increases the agent effect).
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