have a look again to your books. it seems you are a little bit confusing between packs ops and ram air ops
bio,
see my posts above, never mentioned Ram Air OPS but always talked of Ram Air. Ram air = a fluid moving freely around the a/c or entering in it. Be sure that if I DID NOT know what I'm talking about, I wouldn't have written in this thread ... then I can either be right or wrong but just thought that my explanation was the only one to be possible in trying to figure out how the bus gets pre-pressurized on takeoff.
p.s. mentioned a couple of time the RAM air inlet, but wrongly and inadvertently instead of Pack Inlet Scoop.