Any issues with my internal/external overflow design?
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Old 09-24-2013, 04:54 PM   #1
crazymittens
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Any issues with my internal/external overflow design?





Build thread here: http://www.plantedtank.net/forums/sh...d.php?t=395426
  • 125G display, peninsula setup
  • Internal C2C: 17" wide, 5-6" tall, 1" internal width
  • External overflow: 18" wide, 6" tall, 5-6" internal width
  • 3x 65mm holes drilled as high as possible (2" below top edge)
  • Triangular (or curved) gussets
  • 1/4" glass for all of this (recycled from old 30G tank)
  • SC1200 adhesive (approved tank construction silicone)
  • 1.5" bulkheads w. full 1.5" Beananimal drain system (not as pictured)

Final dimensions will change slightly, but that's about it. I did not want to do the 'slot' route as I cannot afford to replace the tank - I am, however, very comfortable with drilling.

Everything I've read (here, reefcentral, googlage) indicates that this should give all the benefits of C2C, enough capacity for 1300-1500GPH (actual), and still retain the Bean drains.

Any critiques? Suggestions? This is the time to tell me I'm wrong!
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Old 09-24-2013, 11:28 PM   #2
crazymittens
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I did a lot of reading/searching on the 'Silent and failsafe overflow system' at RC, and what I am doing is 100% legit, as long as I use the downturned 90-degree elbows. Why? To avoid vortexes - these could suck too much air into the drains causing the siphon to break/have issues. If you submerge the primary siphon enough, shouldn't be an issue. I will try and plan for both.

The only suggested change is from 1" wide to 2", as to mitigate any weir formation issues with high flowrates. Since, at some point in the future, this tank could be converted to salt, might as well add the inch now.


A few design notes for those curious:
  1. The weir should be 1" below the top of the glass rim
  2. The internal overflow should be ~4.5" below the weir
  3. The hole centers should be 2.5" below the weir
  4. Hole centers should be evenly spaced, and as large as workable (to prevent high pressure flow into external overflow box (bubbles = bad for siphon and sump)
  5. The external overflow box should be deeper than the internal, 8" from the top of the tank trim suggested (this is to ensure enough room for plumbing, IIRC)
  6. The opening of the downturned 90s should be centered (vertically) on the holes in the tank
  7. And of course, ensure there is enough room for the plumbing!

By weir, I'm talking about the top lip of the internal overflow box.

If anyone has other input, happy to hear it.


edit: Here's an example: http://www.reefcentral.com/forums/sh...90&postcount=4
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Old 09-25-2013, 10:53 AM   #3
crazymittens
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Oh, and for those concerned about the glass becoming too weak on the bottom panel of the external overflow...I did some tests with 3/16" glass. It took at least 100lbs of pressure (exerted downwards, applied 12" away from the weakest point) to break the glass.

The box is only capable of holding 2-3 gallons, so it would only ever see 20-30lbs of water. No chance of that breaking.

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Old 09-26-2013, 01:06 PM   #4
fishyboy
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Others said it wouldn't work, but I did it on a tank. with 3 1.75" passthrough holes running a 1600gph @ 6 ft pump it was no problem. I limited the pass through holes to one and pressure began to back up but was still "fine". Suggest a few.

Concern.
You NEED to make the external box taller. Yours SHOULD work however once you want screen covers on the fittings it will place the ER/ Durso high enough in the box (has to be high to avoid noise from the passthrough holes) that they will have a tough time going from non-siphon to siphon. My box is a bit different, had 3 holes. used 1 for full siphon, one for return, then put up a internal wier inside the overflow to set overflow water height yet allow the plumbing on the durso side to be LOW in the box. Running like this, all is well.
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Old 09-26-2013, 01:34 PM   #5
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The box will be a little taller, but I get your concerns. The screening will be done on the internal overflow side, so no worries there.

Got any pictures of your setup? Sounds like you did pretty much the same thing as here...except your internal overflow was put inside the external box?
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Old 09-26-2013, 03:45 PM   #6
fishyboy
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My system is very close to yours. My advise is screen both. If one fish makes it through/over your screen they will not like what happens when a full siphon grabs them.

I have the same design + an internal wall inside the external overflow to allow max flow/ ensure the safety can take a full heap of flow without overflowing the box prior to starting full siphon.
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Old 09-26-2013, 03:46 PM   #7
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Basically, In tank wier, leading to external box. In external box it is divided forming another wier. One side of the wier is my safety and gets a trickle. Other side is full siphon and return. If full siphon clogs, water cascades over the wier into the safety drain section.
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Old 09-26-2013, 03:51 PM   #8
the_deeb
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Nice overflow design. I like the low profile internal skimmer box.

I'm not entirely sure about this but my instinct is that you should lower the position of the pass-through holes linking the internal and external boxes. The way it's currently drawn, I would imagine that the siphon line would pull down the water level in the external box to below the top of those holes whereas I think it would run more quietly and efficiently if those holes were always submerged. I think having the water level above the holes would allow them to flow at the full flow rate and the little bit of extra head pressure would help push the flow through those holes, particularly if you're planning to have some screening on them.

Also, I guess there's no reason that you have to have the same number of pass-through holes and overflow holes. The pass through holes are currently the most likely point of failure in the setup (i.e. if a leaf or fish or something gets into your overflow and blocks off one of the holes it's most likely to be one of those screened pass-through holes) so it might make sense to add a few more of those holes for the sake of redundancy.

Oh, and I would put some sort of removable lid on the external box to ensure that the screened holes are the only point of access and that no fauna can jump from the tank or internal box into the outer box.
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Old 09-26-2013, 04:23 PM   #9
crazymittens
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Thanks, fishyboy. I'll only be doing one layer of screening because if a fish can get past what I have in mind, well...they won't be able to. It'll go right up to the lid height, confident nothing will get past (based on experience).

the_deeb - the height of the pass-through holes is the recommended method based on the ReefCentral folks' experience, although I agree, intuitively it seems better to keep them submerged. I believe the reason has something to do with maintaining turbulence (not whitewater rapids) around the drains to reduce the chances of a vortex forming...don't quote me on that.

Further, the reason for the number of holes is simple. I have a 65mm holesaw, and the maximum number of 65mm holes I can fit across that width of glass is 3. Don't forget...65mm is almost 3". Rather large holes.
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Old 09-26-2013, 05:12 PM   #10
fishyboy
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Your hole size/ amount it plenty. way overkill in fact
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Old 09-26-2013, 05:18 PM   #11
crazymittens
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Haha, yup. 1.5" bulkheads going in. Theoretical max flow (in the drains) of like 1500GPH. My weir dimensions limit me to I think ~1200-1300GPH. Well, for optimal skimming, anyways. More = Niagara.

My pumps, after losses, are only spitting out like 750GPH.
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Old 09-26-2013, 05:25 PM   #12
fishyboy
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Your drains will do WELL over 1500. I pushed 1600 thru 1" single siphon with room to spare
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