How does the aircraft get pressurized? Few questions
 

I've read the whole section on pressurization(for the airbus 320), I understand about the cabin pressure controllers, the electrical motors, the outflow valves, all the modes.
WHERE exactly does this cabin pressure come from though?

From the air conditioning packs?
Losing both packs means no more pressurization?

Just some confusion there.
Thanks!

Generally the air for pressurisation comes from the engines via the packs, so yes, no packs means no pressurisation.

As in all modern aircraft except the B787, bleed air is taken from the engine compressor and passed through the air conditioning packs. It is then fed into the cabin.

The control of cabin pressure is by varying the amount of air leaving through the outflow valves.

If you shut down one engine bleed or pack then less air is coming in so less air is let out.

If all packs are shut down then the outflow valves will close to hold as much air as possible but due to leaks the cabin altitude will rise and pressurization will be lost.

Depending on the size of cabin and leak rate the un pressurized rate of climb in the cabin may be 500 to 2000 feet per minute so a descent to lower level is required.

Hope this helps.

Where does the compressed air for the cabin come from in the 787, if not from the engines?

VC10 had compressors driven by the engine gearbox. I think the 787 has electrically driven compressors. I'm sure google could tell you.

Further to FE Hoppy's note -

707/DC-8 etc. as originally certified were required to have air NOT supplied directly from the engine airflow. Instead, turbo-compressors (a la turbosuperchargers) tapped engine bleed air to spin a turbine, which in turn spun a compressor which pumped up fresh outside air for pressurizing the cabin. On 707/720 aircraft these are housed in a cowl bump over the nacelle inlets, on two or three of the engines.

DC-8 Super 70 conversions use engine bleed air a la widebodies and later.

One engine is capable of producing plenty of volume of air to operate the packs one pack is slightly less capable. The MEL altitude restrictions are there more for the purpose of loss of your other source of air and max ability of the apu to operate at altitude. This is a general statement for commercial aircraft in my experience as I am not intimate with the A320. The APU generally produces a lower volume of air than an engine does.

To my knowledge electrically powered compressors. The Generators on the 787 produce much more kva, 500 kva per engine as opposed to the standard 90 or 120 on most engines.

Just to clarify the previous statement, the 787 has two 250 kVA starter/generators per engine, with 120 kVA available via the APU.

Cheers :) EW73

By the way, our AEW&C 737s have 180 kVA generators per engine.