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32 Cards in this Set
- Front
- Back
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What precautions must be taken when working on bleed air systems? |
HOT, don't touch pipes/ducts. Replace crushed seals when refitting joints. Tighten clamps iaw AMM, not what's said on clamp |
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What advantages does using pneumatic systems have? |
Unlimited air supply, lightweight and simple components, weight saving ( no return lines required), no fire hazard, minimised contamination by using filters |
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Which component ensures system pressure does not become excessive? |
Pressure relief valve |
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Which component reduces system pressure to around 1000 PSI? |
Pressure reducing valve |
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Which components remove moisture from the air? |
Water extractor (separator) and desiccant |
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When may a negative pressure be required? |
When requiring a vacuum to instruments or to keep de-icing boots sucked tightly to the wing leading edge |
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What are the two types of air pump and how do they differ? |
Wet and dry. Wet air pumps have steel vanes that are lubricated and sealed with engine oil, the oil being discharged with the air. Dry pumps have carbon self lubricating vanes so require no oil. The vanes are easily broken so a filter is fitted to the inlet to prevent contaminants breaking the vanes. |
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How is oil removed from the air when using wet air pumps within a system? |
By an oil seperator |
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When using engine bleed air,how is a reasonable pressure band retained throughout all engine speeds? |
Toppings are taken from LP and HP stages of the engine. ( LP air always taken, HP also taken at low engine speeds. HP air shutoff when engine speed reaches a point where LP pressure is high enough to sustain demand) |
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What effect will selecting the shut off valve to OPEN have? |
Air will be directed to the turbo compressor. A pressure regulator ensures a constant output. |
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How is airflow controlled in a positive displacement compressor and what can be said about the volume and pressure provided? |
By a series of non-return , produces low volume, high positive pressure or partial vacuum depending on how it is fitted in to a system |
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What is the purpose of the auxillary power unit? |
It provides an independent source of pressurised air whilst the aircraft is on the ground without engines running. On some aircraft the APU can be used in flight as a back up supply of air, hydraulics services in the event of engine failure and aircraft electrical power. |
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Name the 3 types of water separation system |
Coalescer/diffuser, Coalescer/bag, swirl vane |
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How is the mass flow of air controlled? |
By a mechanical mass flow controller which automatically caters for changes in air density, cabin back pressure and engine compressor supply pressure. Pressure drops across the valve will vary the size of the outlet ports and will thus determine the degree of opening and closing. A PRSOV may also be used or a spill valve. |
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How would you recognise an air conditioning pipe? |
Brown and grey label with air conditioning written on it. It has a pattern of four black circles |
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Name 3 methods of filtering air |
Particulate filters, chemical filters (charcoal) and electrical units (ozone) |
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How many outflow valves would we normally expect on an aircraft? |
2. One master and one slave, joined by a sensing line. The valves act as one in unison |
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What other safety valves may be present and for what conditions do they cover? |
Dump valves, on landing, a signal is sent to dump cabin pressure. Ditching valves can be operated to close off all pressurisation valves and inlets should the aircraft ditch into the sea. Inwards or negative pressure relief valve- aircraft are designed to be a higher pressure inside the cabin than outside. If the pressure differential between cabin and outside exceeds 0.5psi, then outside air is allowed to enter the cabin. |
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How does cooling by energy conversion happen? |
The charge air is made to work, driving a turbine which is connected to the compressor or fan within the cold air unit, thus converting heat energy to kinetic energy |
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Precoolers and intercoolers are otherwise known as what? |
Primary and secondary heat exchangers |
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Name the 3 heat exchanger configurations |
Cross flow, contra flow, contra cross flow |
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Name two types of lubricating air cycle machines |
Wet sump (oil used to lubricate). Air bearings where the rotor floats on a cushion of air much like a hovercraft |
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What is the purpose of the compressor in a brake turbine air cycle system? |
To increase pressure and temperature of the air and to act as a brake to prevent turbine runaway |
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How does a turbofan ACS differ from a brake turbine ACS? |
The turbine drives a large centrifugal fan which draws a large amount of ambient air over the precooler. The major advantage is that it can be used whilst the aircraft is stationary on the ground. |
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Describe the basic principle behing vapour cycle cooling |
It relies on the ability of a refrigerant to absorb heat when changing from a liquid to a gas through the process of vaporisation or expansion. The system will contain a condenser (gas to liquid) and an evaporator (liquid to gas) |
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What does the thermal expansion valve do in a vapour cycle cooling system? |
It meters the amount of refrigerant released to the coils of the evaporator matrix and is controlled by its outlet temperature, monitored by a capillary sensor placed at the outlet of the evaporator |
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Name 3 types of heating system |
Exhaust, combustion and compression |
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How does the exhaust heating system work? |
Ram air is blown over the exhaust and the warm air is taken to the mixer unit (mixing valve), where it joins cold air. The warm and cold air mix and are directed to the cabin |
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How does the combustion heating system work? |
Fuel through a PRSOV, which ensures that the fuel is the correct pressure for atomisation. The fuel is ignited by an igniter plug. The combustion chamber warms ram air passing over it |
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How does the temperature controller work? |
The temperature controller recieves signals from the temperature selector (in the flight deck) and from temperature sensors in the cabin, the flight deck and the ducting. If there is a difference, the controller sends a signal to reposition the air mixer valve |
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Which component is bypassed when a manual selection is made? |
The temperature controller |
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Name 2 ways in which humidity can be controlled |
Water separation and water infiltration |
