Re: Cabin pressure

From: (TriStar500)
Organization: America Online, Inc. (1-800-827-6364)
Date:         01 Jun 95 05:00:58 
References:   1
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>If the cabin in a commercial passenger aircraft is
>pressurized, how is it possible to exhange fresh
>air from the outside since I would assume the aircraft
>is somewhat airtight?  Also, is the pressure managed
>by a air-compressor or is it simply "scooped" from the
>outside via some sort of duct-work into the cabin thereby
>generating the pressure?

The air for pressurizing the cabin is 'bled' off of the compressor
sections of the engines. This air then passes through the air conditioning
system and then into the cabin.

The cabin is air tight with the exception of some calibrated leaks and the
outflow valve. The outflow controls how much air is allowed to leak out of
the cabin. Through the pressurization system controller the outflow valve
opens and closes to maintain the cabin at the desired altitude. Typically
the cabin is maintained at about 8,000 feet. The oxygen masks come out if
the cabin reaches 14,000 feet.

That's the quick and dirty answer.