"FACTS NEEDED" Is there "HEAD" Pressure in a CLS?

[platapus]

Here is a question that seems to be debatable, what better place to debate that a message board

Is there head pressure in a CLS?
If so, what is the loss per vertical foot (other than friction)?

If a 10' hose full of water was connected to the inlet of an external pump, and the other end connected to the oulet of the same pump, I could image there being head pressure, the fact that the tank is exposed at the top, would tyhis create pressure?

It would be nice to find that answer to this question so that people can start out with the right size pump for their CLS.

[scubadude]

A true Closed loop will have no horizontal head except wall friction (reduction of diameter input/output) , which basically can be fixed by oversizing your plumbing. Basically the only head that counts is above the intake point, and even then its the vertical plumbing. Now if you have say 1.5" input/outputs and reduce down to say 1" then yes you have head.

I believe there are some really good threads in the archives here on reefland on this topic

[organicreefer]

in my searches-ive concluded that the exact head pressure in any aquarium system is difficult to work out (hey -maybe its just me?)- i figure however much youre going vertically is pretty close-add some for things like splits, 90's and smaller diameter piping.

i wouldnt fret about it too much-as long as youve got a rough idea and try to maximize youre plumbings efficiency youll be fine.

im not positive how much head i have on my closed loop -but its pushing a good amount of water i know that ...

and thats about all i really know about head pressure