"Can we wait for the sketch."
Thats what I have been saying for the only two post I made on this thread. "We need the skecth" Now someone is telling me to wait for it after he promptly tried to explain what is happening:)
"before gradually transitioning to a full pipe scenario."
Not if the arrangement of the pipe is such that it traps air in. If overfill happens and there is trap air, water hammering can occur. very nasty for piping system. You need to make sure that air can escape once overfill happened. But...
Since the return operates by gravity you need to fill all the pipes. You need to put a drawing of the installation. Any comment I make on this without the drawing I consider hearsay. I mean I can not help you.
