Please bear with me on this as I am not quite clear about the expansion tank issue.
First, my water supply is from a well, it comes into the house through a check valve and then into a pressure tank at a tee in the line. The water also goes through filter and softener and then to the house via the hot and cold lines. There is no other expansion tank fitted anywhere.
I find there is a noticeable change in pressure when in the shower, when water is turned on somewhere else in the house.
I am thinking of putting in an expansion tank to hopefully level off the pressure changes when the shower is being used and water is used elsewhere. The extra "cushion" if you like, would hopefully reduce pressure changes.
Would an expansion tank work ok with the connection at the bottom - with the tank verticle. Would the tank do it's intended work if above the floor boards but below sink level. I ask this as I am pushed for suitable space under the floor but could use a small closet to put the expansion tank in.
I don't know if this makes any sense - I hope it does.
Thanks for any and all input.