Quote:
Originally posted by gmat
Flow resistance = water height. Strictly. I insist. (its not the place for a physics course so i wont argue over this)
I know, powerful pumps out there can bear like 11m or even 13m of water.
But not tiny weeny aquarium pumps we usually put in our comps. And there, having a 1m high tower case counts. No matter how you put it you've got 1m of water over your pump outlet (if it's at the bottom). Specially if you have 1/2" or wider all around. And the pressure of this water column will bring down your pump performance. Even in a sealed-closed loop. The pump has to start up and get things moving... And "centrifuge" pumps are not designed to withstand even moderate pressures.
That's why some ppl like Joe buy such powerful pumps.
They're less concerned by water height than by leak prevention... Those pumps dont produce more flow (on paper...) but have a great pressure differential.
My initial point was, putting 2 pumps in the circuit would help reduce that differential and therefore raise flow.
Oops i forgot. Air traps, resevoirs - most ppl have those. And ususally at the highest point. How do they count ? Open loop? Closed loop ?
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gmat, time for a little picture...
Black square = pump
In the left example you are actually lifting the water to another level since it won't flow back and that will require a strong pump.
In the right example you see that there are no lifting involved at all since it is exactly the same pressure on both inlet and outlet of the pump created by gravity. The work the pump has to do is to move the water from left to right (which means it will go up on one side and down on the other).
The diameter of the tube is of absolutely no importance for creating water pressure it's only the height that decides = a 1" and a 1' pipe full of water creates exactly the same pressure per square inch as long as they have the same height.
Regarding reservoirs and so at the top, as long as the water goes back to the pump again is it considered a closed loop (right example)
The reason most people buy oversized pumps are to compensate for smaller things
Now please tell me which part you don't understand.