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Discussion Starter · #1 ·
OK so I found the black acrylic today and I will p/u tomorrow. Not cheep but it is 3/16 cast and black so it fits my needs :)
<O:p</O:p

I am going with (2) 1" drains (I want the redundancy) so I figure that the overflow width needs to be about 15" to handle the two drains. I will do one overflow in the center to hide everything. <O:p</O:p

What spacing do the "Teeth" need to be on the top of the overflow? And how long should they be? <O:p</O:p
 

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Teeth

I made my teeth 1/4 inch thick for both the slots and the actual teeth.
I used 1 1/4 inch for the height. The main thing is that you have enough space in between the teeth to accomodate the drains. You need the minimum total area of the spaces between the teeth to equal the total area of the drain or drains. Here I assume you are

If you have 2 drains each with .5 inch radii then that equates to:

Total Drain Area = 2 * pi * radius^2 = 1.57 square inches.

So if you add up all of the area of the spaces in between the teeth, you should aim for at least a total area of 1.57 square inches.

If the spaces are 1 inch long and 1/4 inch wide then each space is 1/4 square inches in area. That means you need N = 1.57/.25 = 6.28 spaces and teeth if you want the water level to the top of the teeth. Placing the water level at the mid point of the teeth yields twice as many spaces. so you would need 2 * 1.57/.25 = 4*2*1.57 spaces = 12.56 spaces and 12.56 teeth or rounded off you need 13 spaces and 13 teeth. Since each space is .25 inch wide, you need 13 *.25 = 3.25 inches of space width and 3.25 inches of teeth width or around 6.5 inches in length for the total inimum linear length for your overflow. If you want a lower water level you would need to use more teeth and spaces which will increase the total overflow box length. Or you could use longer teeth. You can also use the sides of your overflows for teeth/spaces which effectively reduces the required overflow width.

Given that your overflow is 15 inches wide, you are well over the required minimum overflow width. You could use 1" x 1/4" teeth and spaces all the way down the front of the overflow which would put the nominal water level at roughly 1/4 " above the bottom of the spaces. This assumes that you match the flow of the pump to the1 inch bulkheads so that the water level remains at the bottom of the overflow slots. Just make sure that the bottom of the slots are where you want the minimum water level to be. A pump that is a little too strong will increase the water level above the bottom of the slots; a weaker pump will maintain the water level at the bottom of the slots. A pump that is a little too strong can always be controlled via a gate valve at its output. A pump that is a little too weak may not give you the water turn around that you want and may not allow future expansion. So figure out how many tank turnovers per hour you want and size the pump accordingly, including extra flow for head loss, future expansion like frag tanks or refugiums and performance margin.

ceige said:
OK so I found the black acrylic today and I will p/u tomorrow. Not cheep but it is 3/16 cast and black so it fits my needs :)
<O:p</O:p

I am going with (2) 1" drains (I want the redundancy) so I figure that the overflow width needs to be about 15" to handle the two drains. I will do one overflow in the center to hide everything. <O:p</O:p

What spacing do the "Teeth" need to be on the top of the overflow? And how long should they be? <O:p</O:p
 

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Discussion Starter · #3 ·
:nuts:

Wow. I am no math guy but I think it sounds like I am OK with my 15" overflow (the sides will add some more area as well since my return will be split on each side of the overflow comming over the top) I plan on useing a 1200 gph pump from the sump so I will loose some head but I am thinking it will come down to about 1000 or so.

I currently have a ball value on my drain that allows me to tweek the hight of my display. I am planning on doing that here as well. Any issues with this?

and thanks for all the info!
 

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Valves

I would omit the ball valves. They are not necessary and actually you never want to cut the drain capacity. The overflow teeth/slot depth will control the water level. Just make sure that the bottom of the slots are high enough so that the water level is not too low....I screwed this up in my latest overflow design and as a consequence I need to pump a lot of water into my tank to ensure the water level is high enough. However, all I need to do is block a few slots on each overflow and then I will be able to cut back on the return flow and maintain a higher water level with lower return flow. In other words, it is always easy to reduce capacity but much more difficult to increase it. I would put a gate valve on the output of the return pump instead in case you need to throttle back the pump's output flow.

ceige said:
:nuts:

Wow. I am no math guy but I think it sounds like I am OK with my 15" overflow (the sides will add some more area as well since my return will be split on each side of the overflow comming over the top) I plan on useing a 1200 gph pump from the sump so I will loose some head but I am thinking it will come down to about 1000 or so.

I currently have a ball value on my drain that allows me to tweek the hight of my display. I am planning on doing that here as well. Any issues with this?

and thanks for all the info!
 
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