737 Pressurisation Q

[GearDown&Locked]

Hello all,

I would like to ask you pros a question remotely related to the Helios thread.
I think this is the right place to do it instead of the original thread in order not to disturb a already heated discussion with lame questions.

If there is a problem with the APU bleed air valve when the APU is off and the feed is already done by the engines, would the lost of pressurisation be a rapid one or it would take a longer time to be detected?

How would it be possible to instant and clearly identify a problem with the APU bleed air valve trough the Packs instrumentation (or other)?

Thanks

GD&L

[Cough]

There is a non return valve in between the APU bleed valve and the pressn system so in the event of a failure of a bleed valve then the pressurisation should stay normal. You may get a dual bleed caption on.

[GearDown&Locked]

Thanks for the input Cough.
Is the Dual Bleed sign commanded by duct pressure or is a on/off thingie related to the position of the different valve switches?

GD&L

[Cough]

On off thingy. Eng bleed sw on and APU bleed sw on - Dual bleed lt. Can't remember whether valve position comes into it or whether its solely on Sw position. Duct pressure doesn't come into it.

[Blip]

Illumination of the Duel Bleed light depends on the engine bleed air switch position(s), and the APU bleed valve position (not switch position).

[IFixPlanes]

http://s4.simpleupload.de/thfc20aa5f/737_Dual_Bleed_Light.jpg (http://s4.simpleupload.de/ffc20aa5f/737_Dual_Bleed_Light.jpg)

[Haul By Cable]

Yup, ASFKAP you are right.

"Jurassic Classic" Dual Bleed Light illumination depends on valve position.

For it to illuminate either the APU bleed air valve and the number one engine bleed air valve have to be open, or, the APU bleed air valve, number two engine bleed air valve and the isolation valve need to be open.

Haul.