Duct Pressure For Ground Pnuematic Start

[John H Watson]

So can we assume that the EXT AIR cannot even enter the manifold when the existing manifold pressure (caused by APU or engines) is higher than the injecting EXT AIR pressure?

There are simple mechanical flapper valves (one-way) on the EXT AIR nozzles. Back pressure from the engines/APU will close the check valves. There is no mention of an activating pressure, but they may be lightly spring loaded or, since they are vertically mounted, may just use gravity to assist their closure.

Those videos that Jon posted are from a sim. The pressure drop with both isolation valves doesn't seem correct. Turning off the APU isolation valve with the isolation valves open, for example, will see the pressures on both sides drop quickly (6~8 seconds).
The only difference between the left and right ducts is a small aspiration tube for the TAT probes on the left duct. I don't see how that would drop the pressures so quickly.

The conditioned air valves do oscillate badly if the pressures are relatively equal on both sides. I don't know if the external air valves do.

[Hardy Heinlin]

Thanks.

OK, the valid edit range is now 5 to 50 psi. This is for the external source, not for the arriving pressure in the aircraft. So, for example, when 50 is set, the EICAS will indicate circa 45 (if one half is closed) or circa 40 (both open).

The lower values may demonstrate a more slowly engine spool-up until initial ignition. However, as usual, there'll be no spool-up at all when the pressure is below 16 psi. In that lower critial range there'll be some valve oscillations.


|-|ardy

[Captain_al]

Works for me Hardy, thank you sir...

[fsam]

Hi, as I understand the system function the PRSOV will be closed if downstream pressure is higher than upstream pressure as reverse flow function by bleeding the PRSOV servo pressure (except during engine start). So a lower manifold pressure from - e.g. external source can not close the comanded open PRSOV.
Best regards Ralf

[Hardy Heinlin]

The bleed air features discussed above are now implemented in PSX 10.151:

https://aerowinx.com/board/index.php?topic=4191.0


Regards,

|-|ardy