Closed loop questions!!

[ruck'n'reefer]

I am planning a closed loop with my little giant 3md. Questions: where should I put the pump? Behind the tank at water level? IN the hood? (there is lots of room)
I am trying to minimze head loss.

[Acro]

Bring it over I'll show ya ;)

[ruck'n'reefer]

I was thinking more along the lines of near "my" tank. :D

[Troy F]

I'd put it behind your tank, below the water level. I only have about 10" of vertical head on my closed loop and when the pump is plugged into the right outlet, it is awesome.

[ruck'n'reefer]

Thanx Troy! What happens when you plug the pump in the left outlet? tongue.gif

Is there a reason for having the pump below tank level?

[Troy F]

Pumps don't like to draw up hill, I've never tried it but I believe it seriously effects output performance. Jamie made a point about having it lower than water level by at least some to get the water "falling" into the input, I don't know how relevant that is but it sounded good at the time.

[Acro]

Would it not also be self priming from the water left in the inlet line?

[Troy F]

Absolutely Jamie.

[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.

[reefburnaby]

Hi,

Head loss can occur on closed loop systems because there is always water movement resistance through the closed loop piping. One of the biggest contributors are 90 degree angles because it forces the water to change direction in a small area. This can result in water flow resistance; hence, extra head on to a closed loop system. One 90 degree turn is approximately 1 foot of head (give or take a bit). Another contributor is forcing a lot of water to move through a small pipe. As more water is forced down a small pipe, the velocity of the water flow increases. Water flow resistance increases with velocity.

Hope that helps.

- Victor.

[Delphinus]

Hi Victor, isn't that pretty much what I said? That's what I thought I was trying to say. I said head from bends and the length of pipe (and good point about the ID of the pipe), but no head from a differential between the inlet and outlet. Thus it shouldn't matter where the pump is. Put it on the floor, or put it right behind the tank. Just don't put it higher than the water level.

Sorry. I deal with hydraulic profiles and pipeline models every day for work, so I guess I'm just a little nit-picky about this sort of thing.