Help needed figuring out drain capacity - thanks!

[ibyhousz]

Help needed figuring out drain capacity.
I have a 75rr tank with a corner overflow.
There are 2 drilled holes in the bottom of the tank.
1 hole is 1 3/4” in diameter the other is 1 ½”.
The bulkheads that came with the tank have an inside diameter of 1 1/16” and 5/8” respectively.
How do I calculate the drain capacity based on what I currently have?
Can I change the drain capacity with different size bulk heads?
Your help is really appreciated!
Thanks!
â€"œJoel

 

[spamreefnew]

i dont know any formulas,,,but,,,i know that most overflows that use a 1-1/4" drain pipe(and most do) are rated around 350-400 gph

 

[kraze3]

I believe a one inch drain is about 300gph but thats max. You dont want to have it maxed out. How much flow are you planning to put thru the tank that you think you need more than 1 3/4?

 

[ibyhousz]

I'm not sure how much flow I need yet. I don't think I need more than 1 1/4 I'm just trying to understand how everything works, what my options are, etc. Thanks for the feedback!

 

[cdbias2]

That is a 600gph drain line.

 

[Sk8r]

You can fine tune the system by installing a ball valve on your return line, so that you can 'dial down' your pump if it overpowers your downfall system. If i didn't, I'd have all my water upstairs in short order.

 

[pugmommie]

+1 on the ball valve and get one with unions. They make life much easier!

 

[drparker]

There are two parts that go into the formula. how big the drain hole is and how much linear area is available for overflow, how long is the overflow's top. There are many great calculators located on the home page of Reef Central including the Drain overflow calculator

1 3/4 and 1 1/2 Those are the size of the hole in the glass and match up to a 1 inch and 3/4 inch bulkheads

 

[ibyhousz]

Thanks drparker! That makes a lot of sense.

Now, is there a formula that can figure the drain capacity based on the known hole size and the linear area?

This calculator seems great for design purposes if you are trying to figure out how big to build an overflow and how big to drill your holes based on a desired flow(gph). But I want to know the reverse ... my hole size and linear area's are known and my gph is the unknown.

Does anyone know how to calculate the drain cap in gph based on the known drain hole size and linear area of the overflow?

 

[drparker]

No I don't know the formula, But can use that calculator to back into it. A 1" pipe can drain a max of 592 GPH as long as the overflow is at least 9" long. However any bends, elbows, hose connectors and slime buildup will slow it down. So to be on the safe side I would target 350 to 400 GPH max. To help compensate for the things that will restrict the flow a lot of people will convert to a larger pipe right after the bulk head. I switch to a 1 1/4" pipe. Using the head loss calculator I push about 400gph through mine.