Pressurization Systems

[sky37d]

It's Scarlett

Thanks
My wife would know, but I tend to tune out the old movies she watches.

 

[Cardinal]

Thanks rfresh, this is indeed a good and worthy thread. Many of the new guys I fly with don't have a clue about this stuff, ask the airplane to do something it can't and then cuss at the poor machine because it didn't.

During recurrent preflight training I have actually witnessed a person say that a little 5 inch, 4 bladed electric fan underneath the right wing is what pressurises the airplane. In fact, it is the blower that pulls air across the heat exchanger for our freon vapor cycle machine.

During a discussion about deferred maintenance, the topic of MEL'ing our one and only pack (ACM) came up, somehting that happens with some frequency. The response? "Wow, that would get really hot!" It's frightening out there - Save me.

 

[sky37d]

And I take back everything I said.
It is a worthwhile discussion, and has been very informative.

 

[AV80R]

rfresh - thanks for the post, I enjoyed it! av80r

 

[FL420]

Very informative thread. A good review.

I do believe the following statement implies that bleed air is turning the compressor and/or turbine of the ACM:

By the time you reach cruise, the ACM's are receiving the minimum amount of air through them to keep them turnng.

I thought this was the case for the longest time, probably because the systems descriptions and operations in the Aircraft Flight Manuals have been "dumbed down" for pilots and therefore gloss over the subject. If I'm not mistaken, each ACM compressor and turbine are driven by a powerful AC electric motor. I have never seen it in print but I have deduced this from the high amperage(forget how high) circuit breakers for the pressurization system on the overhead panel on the B757 and the high pitched whine from the packs I can silence by pulling said CB's(on the ground only of course.)

I have never been a plumber and I could be mistaken so if I am I fully expect for someone to set me straight.

 

[lineflyer1]

Very informative thread. A good review.

I do believe the following statement implies that bleed air is turning the compressor and/or turbine of the ACM:



I thought this was the case for the longest time, probably because the systems descriptions and operations in the Aircraft Flight Manuals have been "dumbed down" for pilots and therefore gloss over the subject. If I'm not mistaken, each ACM compressor and turbine are driven by a powerful AC electric motor. I have never seen it in print but I have deduced this from the high amperage(forget how high) circuit breakers for the pressurization system on the overhead panel on the B757 and the high pitched whine from the packs I can silence by pulling said CB's(on the ground only of course.)

I have never been a plumber and I could be mistaken so if I am I fully expect for someone to set me straight.

Actually, the high amperage circuit breakers are for the three phase cooling fans that provide airflow for the heat exchangers while the aircraft is on the ground or when the flaps are extended at slow speeds because there is not enough airflow.

 

[FL420]

I have never been a plumber and I could be mistaken so if I am I fully expect for someone to set me straight.

I was mistaken; I have been set straight; thank you.

BTW. The B757 has 2 packs.