Topic Author
Posts: 132
Joined: Fri Mar 09, 2001 5:46 am

Aircraft Ventilation

Thu Apr 05, 2001 10:40 pm


I was wondering if the air in inflight aircrafts is renewed or if the same air is just cleaned and filtered ?

If it is renewed, How the new air is put in the aircraft? How they increase the oxygen (and the temperature) of the air? Does it have an impact on pressurisation?


I'd rather be flying...
Posts: 372
Joined: Wed Mar 21, 2001 12:53 am

RE: Aircraft Ventilation

Thu Apr 05, 2001 11:22 pm

Contrary to popular belief, acft aren't pressurized like a balloon, but more like a sink with constantly running water, the water is coming in at a pre-determined rate (the acft's pressurization system) and the level of water is controlled by regulating the stopper (the acft outflow valves). Using this method, fresh air is always being pumped in. There is a post prior to this one (Air filters /Heat Exchangers / ECS) in which NKP82 and Airplay provide an outstanding explanation of cooling/heating system operation. After this, the air is basically "pumped in" via the distribution system, and then regulated as it leaves the cabin.

To learn more about pressurization, first study the atmospheric pressure differences on increasing altitude, and the effect of the partial pressure of oxygen during this. Then move to the three methods of pressurization, Isobaric, Differential, and Iso-Differential.

I apologize, I don't have any good links for this subject, maybe someone else could help out? If you can't find any info, just post another question and I will reply in more detail.

"Never trust a clean Crew Chief"
Posts: 1665
Joined: Mon Dec 20, 1999 3:16 am

RE: Aircraft Ventilation

Thu Apr 05, 2001 11:30 pm

Here's a "generic" explanation non-specific to any one A/C type: The air output from the air conditioning systems pressurizes the A/C as well. It is compressor bleed air, so it is at higher than ambient pressure..and very hot. The air conditioning system's job is to cool the air/mix the output with hot bleed air to provide the desired cabin temperature. ---- There is an outflow valve that regulates ( depending on the desired cabin differential ) how much of this air conditioning air exits the A/ it is the only exit point for air form the pressure vessel, except for emergency relief valves. This is how the cabin is pressurized. The air that exits through the outflow valve opening is replenished by the "new" air coming in from the air conditioning more or less a constant flow... ie: the valve doesn't close till pressure builds up, rather it finds a position slightly ajar to let air escape at a set rate comensurate with the pressure controllers commands. This valve is wide open the ground. --- BTW: For a more thorough explanation of the air conditioning itself, see the thread titled "Air filters/Heat Exchangers/ECS" further down on this forum. It was discussed in pretty decent detail.
Topic Author
Posts: 132
Joined: Fri Mar 09, 2001 5:46 am

RE: Aircraft Ventilation

Fri Apr 06, 2001 1:46 am

Thanks a lot for the info! I`ll read the other thread right away.

I'd rather be flying...

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