Custom Tank Drainage Question

[shaginwagon13]

I'm am in the process of getting a 150 Gallon tank built. The dimensions are:

48L x 24W x 30H and I have one internal overflow going in the middle of the left panels. (see picture)

My question is this:

As of right now I have 1 – 1.5� bulkhead for the Drain and 1 – ¾� bulkhead for the Return. Should I have it built with 2 - 1.5'' bulkheads for the Drain and then leave the 1 - ¾� the way it is?

P.S. In the picture there are 2 overflows (1 at each end) however mine will only have one overflow

[Sisterlimonpot]

I can't see the picture however, 2 ovewrflows are better than one.

[shaginwagon13]

Originally posted by Sisterlimonpot
I can't see the picture however, 2 ovewrflows are better than one.

I know that but only one overflow is possible so my question is should I have 2 bulkheads for drainage and 1 bulkhead for a return

OR

1 bulkhead for drainage and 1 bulkhead for a return

[turretdr]

By having 2 for drain, you reduce the possibility of a clogged drain. You could even leave just the 2 holes, use both as drains and have your return come over the back.

[Aquarist007]

Originally posted by shaginwagon13
I know that but only one overflow is possible so my question is should I have 2 bulkheads for drainage and 1 bulkhead for a return

OR

1 bulkhead for drainage and 1 bulkhead for a return

in your case the limiting factor in your drainage is the surface area of the overflow so it really should not make much of a difference having the two bulkheads for drainage.

[shaginwagon13]

Is it a gammon problem for drains to loose syphon? I have 2 external overflows on my big tank and they always loose syphon so I'm trying to avoid this with this tank...

[der_wille_zur_macht]

Internal overflows *can't* lose siphon, since they don't depend on it to function.

What are you using for a return pump? Do you know what your target is for flow through your sump?

A single 1.5" drain can handle a lot of flow, and is big enough that it'll be hard to clog. IMHO if the tank is already built like this, you're totally fine.

[quotein your case the limiting factor in your drainage is the surface area of the overflow[/quote]

Weir length is limiting really only in terms of noise (once you start trying to put more flow over a weir, it just gets louder - it won't stop working), and if his is toothless (as in the picture) it'll handle a lot more flow, more quietly, than the typical overflow with teeth on the weir. Many of the "rules of thumb" (including the one used in the RC calculator) for weir size are extremely conservative, and many reefers put far more flow over a small weir than these rules would typically recommend.

[Aquarist007]

Originally posted by der_wille_zur_macht


[quotein your case the limiting factor in your drainage is the surface area of the overflow

Weir length is limiting really only in terms of noise (once you start trying to put more flow over a weir, it just gets louder - it won't stop working), and if his is toothless (as in the picture) it'll handle a lot more flow, more quietly, than the typical overflow with teeth on the weir. Many of the "rules of thumb" (including the one used in the RC calculator) for weir size are extremely conservative, and many reefers put far more flow over a small weir than these rules would typically recommend. [/QUOTE]

Okay--I'm trying to grasp this because it is much different then I have been told----and you have the experience way way more then me
Lets take the eg of a 1 inch gravity drain--the max you will get out of that is 600 gph or so. If you add two one inch drains then you have a flow of 1200 gph out of the overflow
What I don't quite see is how using the same overflow box won't keep up with double that flow and drain the drain pipe in the overflow box??

[der_wille_zur_macht]

The limiter is the diameter of the plumbing to the sump. Most people think of this in terms of the diameter of the bulkhead they install, which is an OK assumption given that the rest of your plumbing is at least this big. As you increase the flow you are trying to handle with a certain diameter pipe, the amount of air sucked into the pipe will decrease. This will happen until you reach the point where the pipe has no air in it and is essentially running as a full siphon instead of a "gravity drain." These are the numbers you're quoting - around 600 gph for a typical 1" bulkhead. This number increases in a roughly linear fashion in relationship to the area of the pipe's cross section, NOT the diameter - so, for instance, a single 1.5" drain can handle more than twice what that 1" drain can (around 1300 gph).

But talking about capacity of the drain plumbing is a different issue than capacity of the overflow weir.

Within reason, the length of the weir (i.e. the overflow box itself) is NOT limiting. If you try to flow more water over it, it'll handle it - but after a point, it will just get more noisy as the water splashes over it.

There is, of course, an ultimate point at which it'll be overwhelmed, but that's typically going to be well beyond what we are able to push in our tanks.

Perhaps I was confusing when I referenced the RC calculator. It recommends a drain size and a weir length ("linear overflow length" is the term used by the calculator for weir length.) I do feel that the drain size portion is totally correct, but that the weir length portion is extremely conservative. That is, it recommends a weir far longer than necessary for quiet operation.

[der_wille_zur_macht]

I apologize if my explanations are hard to follow - sometimes they're wordy. Let me know if that is still confusing and I'll see if I can re-word it.

[Aquarist007]

Originally posted by der_wille_zur_macht
I apologize if my explanations are hard to follow - sometimes they're wordy. Let me know if that is still confusing and I'll see if I can re-word it.

crystal clear for me

thanks for taking the time to explain.

[Gtstricky]

I was just about to type up the same answer as der_wille_zur_macht but then I realized I don't know any of that stuff. He says your good so you are good.