A320 Hot Air Pressure Regulating Valve Failure
 

Hi everyone

In the event of a failure of the A320's Hot Air Pressure Regulating Valve in the closed position, DSC-21-10-40 P 2/2 states the following:

"Optimized regulation is lost. Trim air valves are driven to the fully closed position. Pack 1 controls the cockpit temperature to the selected value and pack 2 controls the cabin temperature (FWD and AFT) to the mean value of the selected temperatures."

My question is, how can an individual pack supply a specific zone given all zones are supplied from the mixer unit, itself supplied by both packs?

If I'm not mistaking, I think the pack 1 supply first the cockpit, and pack 2 the fwrd and aft cabin.

Then the air is sucked out of the different zones and recirculated via the cabin fan to the mixer unit.

I do agree that when looking at the AC diagram, it's a bit confusing. (not obvious at least)

(Don't pay attention to my above comment, I'm wrong)

Dispatch with the valve closed is allowed under the MEL. Initially the cabin temperature is a bit difficult to set exactly but once in the cruise it soon settles down.

CReed, my understanding is that even though the packs are fed firstly into the mixer unit, the location of the pack inlets and zone outlets allow for a certain "ballpark" temp control between front (cockpit) and rear (FWD Cabin and AFT cabin).

The schematic shown in DSC 21-10 ARCHITECTURE would seem to back this up, though of course this diagram is a simplification and may not show accurately how this rough zone temperature control is acheived.

Hi Kerosine

Yes, I believe you may be right. I asked a friend who has a copy of the AMM for his insight last night and whilst it doesn't explicitly describe the geometry of the mixer unit, its schematics appear to imply the presence of some sort of permeable partition within. It would seem this partition biases the output from pack 1 to the cockpit zone and that of pack 2 to the cabin zones. The description of the functionality of the mixer unit flap would seem to support this. Take a look for yourself:

http://i.imgur.com/D5gYeva.png