calculating flow

[thejuggernaut]

I am in the process of building a new 120 tank. It is gonna be drilled with overflow. I want to know what kind of flow I would get through 3/4" drains. If I can get enough flow through two of these drains I would like to stick with just two, but I would be willing to drill more if need be. I am wanting somewhere in the neighborhood of around 600-700 gph. Also, I would like to know what brand of pump I should get. While I dont have a million dollars laying around, I would rather spend 50 bucks more to get a good pump. Anyhelp would be appreciated.

 

[MarineTeng]

here's the RC calc for that
http://www.reefcentral.com/calc/drain.php?gph=700&drain=Submit
two 3/4" drains sounds about right to me, i think my overflow is either 1/2" or 3/4" and runs 300 gph and i don't think i'm maxing out the flow, but another factor on overflow flow they call linear overflow size is basically the perimeter of the overflow, might want a more pro opinion on this

 

[Slickdonkey]

Better to oversize than undersize if you can. This will give you more flexibility if you want to change things in the future.

 

[thejuggernaut]

yea ive seen that flow calculator, does anyone know where i can find one that calculates flow for more than one drain. I would imagine that a 1.5" drain would flow differently than two 3/4" drains.

 

[Meche]

I would imagine that a 1.5" drain would flow differently than two 3/4" drains.

Much differently. You want to look at cross sectional area. Area=pi*(diameter/2)^2. The 3/4" will flow 1/4 as much as the 1 1/2" tube. Two 3/4" will only flow half of what a 1 1/2" will.