Packy,
Now and hopefully the final question at this point, putting the expansion tank on the boiler side of the circulator, considering I am re-piping this whole job I would like to have everything correct. Now does the placement of the expansion tank relative to the physical location of the boiler have to be above everything or is that just where the plumber put it? Referring back to my final drawing if I take the expansion "off the return manifold" tank throw a tee between the circulator (suction side) and the low water cutoff all I would have on the return side would be the manifold correct (aside from everything else outlined in blue: such as cold water supply/feeders etc.)
as always
thanks,
Joey



Edited 2 times.

without getting too crazy technical..
when the circulator kicks on it can create a temporary low pressure behind it. if the auto fill valve senses a low pressure it can kick on and shoot some un-needed water into the system. this will cause the system pressure to rise slightly and stay there.
so to avoid this happening you locate the expansion tank close to the back side of the circulator. so when the circulator creates a very small pressure drop, the expansion tank will make up the difference.
this is my understanding of why..
personally, I would not change what you have. I has worked well for years and will continue to work just fine. I would however remove the expansion tank, put a nipple and ball valve and put the tank back. take the handle off the valve so it won't get closed but can still be closed with a pliers when the tank needs replacement.
did you get my e-mail?

And support the weight of that tank properly.