Momentum is not pressure, and therefor the equalization of pressure in the pipe has nothing to do with where that momentum goes.

think of all the little air molecule thingies as being
little rockets flying around inside the big old pipe thingie.

some of the rockets fly north , some fly south , some fly east , some fly west , some fly down, the others fly up.

the little rockets that fly up , dont have far to go.
but the little rockets that fly down have a much further trip to take.
most of the litle rockets begin their trip by flying down but they have a harder and harder time finding a place to stop because of all the other rockets getting in the way.

but a few of them get to go all the way down.

and because the little rockets all move inside the pipe the pipe moves , up.
here we go again , the equalization of pressure inside the pipe

has everything to do with the momentum

the pressure is the air , the air mass is what moves , and
the momentum of the moving mass of air

is the momentum.
3/4 inch of dust build up on the moon in 4.527 billion years,LOL and QM is fantasy science.