A320 - pneumatics & pressurization doubts
QUESTIONS ON - PNEUMATICS & PRESSURIZATION
Dear all . Kindly help me with the following A320 queries . Thank you for your time in answering
1. SOP - PARKING - If the APU is used, set the APU BLEED pb-sw to ON immediately before engine shutdown to prevent engine exhaust fumes from entering the air conditioning.
How can switching ON APU BLEED just before (immediately before) engine shut down prevent it from sucking engine exhaust into air conditioning ?? . My confusion is if i start APU bleed 10 minutes before engine shutdown , wont the engine exhaust still be sucked into the air conditioning ? I am not able to understand this logic
2. Regarding Air conditioning PACKS, what ever selected on the PACK FLOW SELECTOR, the system delivers higher flow during single pack operation. So if we have an engine failure the pack on the operating engine side will go on higher flow, but now if I open the cross bleed valve sine both packs are being supplied by operating engine , both packs go to normal flow (since this is not a single PACK case) . Am I correct ?
3.Safety valve relief setting is 8.6 psi (limitation) Does safety valve work for excessive negative Delta P also ? If yes where is this value given ?
4.FCOM SYSTEM DESCRIPTION, PRESSURIZATION CHAPTER - Note: The safety valve opens when the indicated ∆P is between 8.9 and 9.7 PSI. The range is due to the reduced accuracy of ∆P measurements (in MAN mode), combined with the
decrease in ∆P that occurs immediately after the safety valves open.
I understand this means that in MAN mode the safety valve will open when the Delta P indication is anywhere between 8.9 to 9.7 psi , This is applicable only to MAN mode of operation. When in AUTO mode the safety valve opens at 8.6 psi . Am i correct?
4. With both CPC failed the FAULT light on the CAB PRESS panel MODE SEL pb switch illuminates (indicating both SYS 1 & 2 failure)
When MODE SEL pb sw is put to MAN, will the FAULT light extinguish ? In the simulator I have seen the FAULT light remains illuminated , however some maintenance manual shown to me indicated that the Fault light will extinguish ( however this Maintenance manual shown to me was quite an old revision) .
Some A320 Question Bank also mentioned that the FAULT light extinguish when the MODE SEL is set to MAN
But as per my understanding when CPC MODE SEL put to MAN the FAULT light does not extinguish but stays illuminated . AM i correct?
Thank you for your kindness in taking the time to answer my questions.