Happy new year to all!
Hopefully i am allowed to state my question here, even if i am only the user of the system - but after doing a lot of research i still have no answer:
In flight (ferry) isolation valve close, left bleed air sws close.
APU bleed air sws off.
The checker asked what pressure i expect to be indicated on the left duct.
My answer was 0 psi.
But in fact it was somewhat about 10 psi.
He told me, that this was the same with all 737-800 in which he tried this out and he (nobody!?) has an explanation for that...
Sholud the prsov's be a 100% close? Or is there always (or often?) a rest of pressure leaking through the valve even if the switch is in position close?
Or does it has something to do with pressurisation of hydraulik fluid or water tank?
I thought, that you are the guys who may have an answer to this!