Pneumatic System Flashcards
Pneumatic System Utility
air conditioning pressurezation aereofil and engine autoicing air turbin motors pneumatic rams hydraulic resercoir and potable water cargo comportment heating
Air condition system
regulate the Temperature, quantity and quality of air.
Reason why it is pressurized
- fly high altitude
- high rate of climb and descent with small different in pressure change
Require in a cabin
- rate of 1 lb per min per seat in normal circustance 0.5 lb in case of failure
- Temperature 18 - 24° C
- Relative Humidity around 30%
- Carbon Contamination less than 1 in 20000
- Ventilation during ground and unpressurized period
- Duplication
- Adeguate supply
Unpressurized system
Ram air System - air is introduce from a fwd air intake
some of this ram air is heated by exhaust or combuston heater but is very important that they don’t eneter in conat with ext and air used in combustion.
it use the air also for windscreen, there is also a air inlet when the airplane is in the ground
Combustion heater
Ram air is blowed with a fan inside the combustion chamber and
bleed air
the bleed air in a jet airline ii is take from the high pressure compressor:
- the normale stage where the air is taken in Low pressure stage in the beginning of N2 5th stage
- in case of there is not enough pressure the air is take from the HP stage always in N2 9 stage
- every engine has a seprate circuit in case something happen they ar enot connected
- from the fan is take some air to cool the T
- also the APU can deliver bleed air
- negative part of this system that in this way air is taken from the engine so the effiency is reduce
Low Pressure Stage
the flow is controlled by a Check Valve that avoid the possible air that come from the HP stage to enter again in the system and create problems.
HP Pressure Stage
the HP pressure stage is used only when the air is not enough and is regulated by the use of a HP Shutoff valve that make it use the valve or not
Engine bleed air valve
it is the separation point between the engine and the pneumatic system
Fan Air
it is used to cool the hot air temperature coming from the HP compressor, it is link with a fan air valve that it finish in the precooler system before it enter in the Manifold and than to the user
Manifold
air ready to be deliver to the user with a 30/40 PSI. The different engine are separate in a isolation valve. Each user normal is charge with a specific engine, in case of problem the valve can be open.
Air cool system
uses the principles of energy conversion and surface heat exchange. Hearth is the Cold Air Unit (CAU) tht use the turbo-compressor, a possible example is the BOOTSTRAP. CAU is also call air cycle machine (ACM).
Turbo-compressor (Bootstrap)
The low pressure bleed air (or air from a blower)
is pre-cooled in the primary heat exchanger then its pressure is invr by the compressor. This is
done in order to make the energy conversion (i.e. heat and pressure to work) process across the turbine more efficient. Between the Compr and the turb is the 2nd heat exchanger that remove any excess temperature rise across the compressor.
After the 2 exchange heat the air is going in the turbine. To have a sufficient airflow across the cold air unit when the aircraft is on the ground or at low speed in the air, a fan is provided to draw in air through the ram air or ground cooling air ducts. The ram air doors may be opened and closed according to flap position or modulated automatically by signals from the temperature control system. In case there is a need of cold temeperature, there is a bypass control valve for temperature.
Temperature/ Pressure
the temperature and the pressure varing in the unit TInizial = 168 P i = 30 T final = until + 2 P final = 16.6
Ram air conduct
it is a present a fan that make rotate the compressor
Water separator
Located downstream of the turbine, the water separator removes the excess water which condenses during the cooling process. This is a problem at low Alt and when running the system on the ground with high humidity. A safety valve is provided to ensure that the flow of air to the cabin is safeguarded in the event of the water extractor icing up. In some installations a temperature sensor controls an anti-ice bypass valve which allows hot air to pass directly into the airflow between the turbine and the water
separator to prevent icing.
Humidificator
In aircraft operating at high altitudes for long periods of time it may be necessary to increase
the moisture content of the conditioning air from the 1-2% relative humidity
Temperature Control
The temperature of the air entering the cabin is usually achieved by mixing hot air with cooled
air. There are two basic methods of temperature control, mechanical and electromechanical.
The simple non-automatic manual method consists of valves which are manually positioned to
regulate the temperature by mixing hot and cold air prior to it entering the cabin. Automatic
control of the cabin, flight deck, cargo holds etc. temperature is achieved by comparing a pilot
selected temperature with the temperature of the mixed air inlet to the cabin
