hot water register piping

Lenny

Your site is the best I have seen, as far as heating information, it is nice to know that you are here to help. Thought I would ask for your help on a situation that I have yet to find an answer.I have recently purchased some additional heat registers for my house. Question is:
On two of the "new" registers the the pipes were routed differently than my existing registers. My existing registers have the inlet and outlet pipes tapped into the bottom of both sides. The "new" registers have one pipe on the bottom, and one on the top of the other side. Since I cannot remove the fitting (siezed up) on the new ones, can I leave them with one pipe on top and the other on the bottom? If so, does it make a difference which side is the supply and which is the return? Also have heard of a valve that allows the supply and return to be routed together through only one fitting. Is this valve available and would it also solve my problem?
Thank you for your time.

Mike T., Swampeast MO

Install the supply (and valve) at the top connection and the return at the bottom.