how to calculate flow rate of over flow box

magma · 10-20-2004, 03:17 PM

Hi,
I made my own overflow box from two lee's specimen containers: one large(7" L x 3-1/4" W x 6" H) and one small (5-1/8" L x 2-1/2" W x 4-1/2" H), with the small one inside the tank.

How do I calculate the approx GPH of my overflow box?

The linear overflow size is about 10" (Is that correct?), so does that mean my overflow box can handle 650 gph? I used the reef central overflow size calculator and just worked backwards.

Thanks

yousuredo · 10-20-2004, 05:04 PM

if you go to RC web site they have a caculator for several things including this
here is the link

wanareef · 10-22-2004, 05:44 AM

Also what size is the BH going out? That would also have some affect on the flow.

magma · 10-22-2004, 05:05 PM

it would be a 1" bulkhead

davidc · 10-25-2004, 10:52 AM

Quote:

Originally Posted by magma

it would be a 1" bulkhead

The bulkhead is the ultimate limiting factor. Even if your overflow is 24" wide, you still aren't going to flow more than a 1" pipe will allow!

It sounds like you are using a U-tube to siphon from the inside box to the outside box. If so, then this tube will also be a limiting factor. If it is a 3/4" tube, then it's gonna be able to flow about 330gph according to the reefcentral drain calculator. No matter how big your overflow box is, the size of the siphon is what matters.

I just built one from scratch myself. I used scrap acrylic I had, and it will have a 3/4" bulkhead. Mine will only flow about 250gph because of it's design though.

magma · 10-25-2004, 01:06 PM

My u-tube 1-1/4" OD and my stockman standpipe is 1" also. If I stay with 1" pipe for the rest of the plumbing coupled with a Mag 7, I may be able to get a flow rate of 600gph.

Is this too much for a 20g tank? Should I use 3/4" for the rest of the plumbing to slow it down?

Thanks for the replies. I just started to get into reef tanks, and I've never done any plumbing before. When I go to Home depot to look at the plumbing parts, I get really confused.

davidc · 10-25-2004, 04:27 PM

Quote:

Originally Posted by magma

My u-tube 1-1/4" OD and my stockman standpipe is 1" also. If I stay with 1" pipe for the rest of the plumbing coupled with a Mag 7, I may be able to get a flow rate of 600gph.

Is this too much for a 20g tank? Should I use 3/4" for the rest of the plumbing to slow it down?

Thanks for the replies. I just started to get into reef tanks, and I've never done any plumbing before. When I go to Home depot to look at the plumbing parts, I get really confused.

don't forget about the head pressure loss (from pumping the water up maybe 3-4 feet) - you're probably going to be more like 500gph or less. Even then I would say that is a LOT of flow for a 20G! I'm only getting about 600gph for my 72G, to give you an idea. That is low for my size tank, so that is why I built the overflow mentioned above

With that much flow, you might want to split it into 2 or more outlets so it doesn't blast anything too hard.

wanareef · 10-26-2004, 03:34 AM

Just remember, that the "flow" in the tank is not realized by the return. This is accomplished by; PH's, Streams, CL, wave box or some other form of machanical means. Lots of guys mistaken this and try to get the most water out and back into the tank- and IMO is not needed, hard to do without creating too many bubbles, (even with baffles). You do want to flow the most you can but for skimmer filtration, heating or whatever you have in the sump (that is if you have one)

davidc · 10-26-2004, 09:38 AM

I try to use my return to circulate as much of the tank as possible, simply because I don't like powerheads/etc... in there. If my return flow is high enough, I can get most of the tank circulated. Some parts more, some parts less.

Eventualy I want to build a true wavemaker - one that will actually create a wave instead of just having powerheads come on and off. I think that the waving motion would be just as much of a step towards nature as a high flow would.