[Delphinus]

WHy would you get head loss in a closed loop? You'll only get head pressure basically from the length of pipe and from corners such as 90-degree bends and such. For example, each foot of pipe is equivalent to a certain amount of head, each 90-degree bend is equivalent to a certain amount of head (although I forget the exact conversions). But as far as head pressure from the position of the pipe -- so long as the pipe is filled, the inlet and outlet are at the same level (hence "closed" loop), so no head pressure.

That said, I'm not so sure I would have the pump above the water surface; closed loop or no. I agree with Troy, I think this would serve to restrict the input, which as we know is not good for pumps.