15.20 fire protection systems Flashcards
what is a fire zone?
designated by the manufacturer to require fire detection and/ or fire extinguishing systems as well as a high degree of fire resistance
what is thermodynamic turbine failure?
an upset to the quantity of of air used to cool down combustion temperatures, turbines can melt causing a sudden loss in thrust
what can cause thermodynamic turbine failure?
Ice, excess bleed air etc
what is mechanical turbine failure?
fractured or thrown blades
what can occur as a result of mechanical turbine failure?
damage to the turbine housing
what is contained in a complete fire detection system?
fire detection and extinguishing
what are the common detectors used?
overheat
rate of temp rise
flame detectors
what are the two most common types of fire detection systems?
spot and continuous loop
how does a spot detector function?
individual sensors to monitor a fire zone
which aircraft use a thermal switch or thermocouple design?
older
what is the structure of a thermal switch design?
A thermal switch system comprises one or more lights energised by the aircraft’s power system and thermal switches that control the operation of the light(s). These thermal switches are heat-sensitive units that complete electrical circuits at a set temperature
how are thermoswitches connected?
They are connected in parallel with each other, but in series with the indicator lights
what is the disadvantage of the thermocouple?
A thermocouple depends on the rate of temperature rise and does not give a warning when an engine slowly overheats, or a short circuit develops.
how is the wiring system divided for a thermocouple?
Detector circuit
Alarm circuit
Test circuit
what principle do optical fire detectors function on?
they alarm when they detect the presence of specific radiation emissions from hydrocarbon flames
what are the two types of optical fire detectors?
Infrared (IR) and ultraviolet,
how does a pneumatic fiure detector function?
The sensing element consists of a closed helium-filled tube connected at one end to a responder assembly
gas pressure inside the tube increases until the alarm threshold is reached. At this point, an internal switch closes
how does an average sensing function work?
it is activated by the expansion of a fixed volume of helium gas inside the detector
how does discrete temp sensing function on pneumatic fire detectors
Discrete sensing is accomplished using a hydrogen-filled core material in the sensor tube.
Hydrogen is released from the detector core if a small section of the tube is heated to a discrete temperature
This outgassing in the core will increase the pressure and activate the alarm
are the discrete and average temp sensing in the pneumatic fire detector reversible?
yes
what are the two widely used types of continuous loop detectors?
fenwal
kidde
what is the fenwal systems structure?
The Fenwal system uses a slender Inconel tube packed with thermally sensitive eutectic salt and a nickel wire centre conductor. Lengths of these sensing elements are connected in series to a control unit
how does the fenwel system function?
When an overheat condition occurs at any point along the element length, the resistance of the eutectic salt within the sensing element drops sharply, causing current to flow between the outer sheath and the centre conductor
how does kidde differ from fenwel?
it has two embedded wires
what do the two wires in the kidde system connect to?
one to the tube
one to the fire detection control unit
how is a detection system tested?
through a switch in the cockpit
what is the benefit of a dual loop system?
both must sense the alarm condition to know there is a fire limiting false alarms
what must all engines have in terms of extinguishers?
a two shot system
how does a fixed fire extinguisher function?
it gives of an inert gas to not support combustion
why do we use halon 1301?
it is not corrosive, toxic etc
when can cylindrical fire bottles be used?
when space is a concern
what is the typical fire bottle shape?
cylindrical
what is installed in a discharge valve of a fire bottle?
a cartridge (squib)
tangible disc type valve
what are the other types of available discharge valves on fire bottles?
solenoid-operated or manually operated seat-type valves. Two types of cartridge disk release techniques are used. The standard release type uses a slug driven by explosive energy to rupture a segmented closure disc
how can you know the pressure of a fire extinguisher charge?
A simple visually indicated gauge is available, typically a vibration-resistant helical Bourdon-type indicator
when is a two way check valve used on fire bottles?
when a two shot system is in place
what occurs when a fire switch is activated?
the engine stops
the extinguishing system is armed
