A320 pneumatics

[tubby linton]

I was having a look at the chapter on Pneumatics in the FCOM and I was wondering what the temperature and pressures are of the air when it initially is fed into the pneumatic system from the engine and then having passed through the pre-cooler . Ecam only shows pre-cooler outlet temperature and pre-cooler inlet pressure.
Would any of you be able to supply the figures involved?

[ASRAAM]

The FCOM example picture shows 190 degrees C

[tubby linton]

That is the temperature of the precooler output though. i suppose my question is how efficient is the precooler in reducing temperature and is there any pressure drop across it.

[Amadis of Gaul]

Does it really matter? There isn't a thing you can do about pre-cooler efficiency (or lack thereof) from the flight deck.

[tubby linton]

I am asking because I was interested to know. I know the whole thing is automatic, but I would like to know how efficient it is. Judging by the size of the cooling vanes on the pylon I would imagine that the temperature change is not huge, but is there a pressure drop across the unit? There is obviously a pressure reduction from the input of air from the engine to the final flow of air to the cabin.

[Amadis of Gaul]

Works good, lasts a long time. Good enough for me.

[tubby linton]

I have never had a problem with it but an article ina Fast magazine from Airbus talks about operational interruptions.

[A33Zab]

Don't have figures for A320 but A330 system setup is more or less identical.

The displayed pressure is called Pr (Regulated Pressure) and is the pressure downstream of the (PRV) Pressure Regulator Valve.
The pressure upstream the PRV is called Pt (Transferred Pressure) this pressure is not displayed but is an input to the BMC.
The measured Precooler Outlet Temp is displayed and also regulates the cooling air(fan outlet air) by a modulating valve (FAV)

The values of the transferred pressure and temperature at TO could go up to ~145psi/~370°C.

Normally the PRV will reduce this pressure to 48psi and the Precooler cools it down to 200°C.
Some specific system demands/overpressure/overtemp will have an effect on the output values.

[tubby linton]

Thank you for the info.
My next question is how is this output pressure (Pr)reduced to the pressure that finds it way into the cabin, is it reduced in the pack?

[A33Zab]

By the FCV (Flow Control Valve) before air enters the pack, although the FCV regulates flow instead of pressure there is a relation between output pressure and flow.

The cold pack discharge air is mixed with hot air regulated by a TAPRV (Trim Air Pressure Regulating Valve) which regulates to 4 psi above Cabin Air Pressure.

[tubby linton]

A33Zab if the flow is excessive how does the FCV regulate the flow? is there a return or vent or does the valve move to limit the flow?
Within the pack are a Main Heat Exchanger and a Primary Heat exchanger, would you be able to give values for temperatures and pressures within these sections and also at the outlet of the pack turbine please?

[Amadis of Gaul]

Tubby, are you trying to design a better PACK or what? Seriously, what difference do any of those values make?

[tubby linton]

I am just trying to get a better understanding of how the system works Amadis. I must have been asleep when somebody explained it to me years ago.

[A33Zab]

The flow is limited depending on demand.

The exact press/temp values depend on zone demand, cargo cooling demand, pack demand, other pack state and bleed source supply state and system state, but to give you an general idea:

http://i474.photobucket.com/albums/rr101/Zab999/Pack_Press-FlowGraph_zpsbe05769b.png

[tubby linton]

That is a great illustration of how the system functions, where does it come from?

[IFixPlanes]

For example here https://www.myboeingfleet.com, https://w3.airbus.com or Lufthansa Technical Training (http://www.ltt.aero/en).

[tubby linton]

Unfortunately I do not have access to any of those links. I asked the company engineering training school for info and never got a reply.

[Amadis of Gaul]

It's not actually possible to understand how PACKs work other than to know that it's by the PFM principle.