condensate return

It's not really a problem. Provided the pipe is big enough and pitched properly. There is relatively little condensate, and it flows along the bottom of the pipe. If too much concentrates or it fills too much of the pipe -- that is, the pitch isn't adequate or the pipe is too small -- the moving steam will pick it up and slam it against the next handy elbow -- water hammer. Otherwise, it just flows quietly in a shallow stream on the bottom, and the steam zips over it and doesn't disturb it.

jumper said:

I wonder if liquid from higher floor can obstruct steam at take off?

Indeed it can -- if the takeoff is not properly plumbed. If it is correct (within 45 degrees of the top of the pipe), then no.

Sounds like we're talking about 2 separate issues here.

If there is 1 PSI steam pressure applied to the bottom of a water filled pipe, yes, it will raise that water column 2.31 feet.

On the other hand, if a pipe is filled with steam and is vertical or has sufficient pitch, the small volume of returning condensate will flow downhill even though the majority of the pipe's volume is filled with steam.

It's a matter of gravity. Water is heavier than steam.