Calfo Style Overflow boxes

[spider86]

Im getting ready to drill a 37gal. I will be putting 2 3/4 bulkheads for the drain. Now Im trying to figure out how Im going to build the overflow box. Im not sure that I need a calfo type because of the smaller tank. Do you think 2 corner pvc pipe overflows would be suficient? How many gph do you think it would drain?

 

[ReefMeister2]

<a href=showthread.php?s=&postid=8158609#post8158609 target=_blank>Originally posted</a> by spider86
Im getting ready to drill a 37gal. I will be putting 2 3/4 bulkheads for the drain. Now Im trying to figure out how Im going to build the overflow box. Im not sure that I need a calfo type because of the smaller tank. Do you think 2 corner pvc pipe overflows would be suficient? How many gph do you think it would drain?

~600 gph total if using 6" quarter pipes in 2 corners
~800 gph total if using 8" quarter pipes in 2 corners

If room will allow, I'd drill for 1" bulkheads for the drains. You can always downsize, if need be, but you cannot go larger once the hole is drilled (you may decide you need more flow in the future, such as with an SPS tank, etc.)

 

[spider86]

ReefMeister, Is that 600 gph per overflow? So I would have 1200gph if I did 2? I have the drill bit on the way to drill 3/4 bulkheads, so I have to go with the 3/4's.

 

[ReefMeister2]

<a href=showthread.php?s=&postid=8159164#post8159164 target=_blank>Originally posted</a> by spider86
ReefMeister, Is that 600 gph per overflow? So I would have 1200gph if I did 2? I have the drill bit on the way to drill 3/4 bulkheads, so I have to go with the 3/4's.

NO, unfortunately if you are doing corner overflows, then you are only using "quarter" pipe sections...so it is 300 gph per 6" quarter and 400 gph per 8" quarter overflow. It's a trade-off; what you gain in simplicity and aesthetics, you lose from very limited linear inches at the top surface. The best you could do is get 800 gph out of dual corner overflows made from 8" pipe.
But I'm guessing that should be more than sufficient for your size tank.

These numbers are calculated using basic geometry and the overflow calculator on RC's home page.

 

[spider86]

Thanks ReefMeister! 800gph would be more than enough for my 37gal. Anyone know if HomeDepot sells 8 inch black pvc? Or where else do you find the stuff.

 

[ReefMeister2]

<a href=showthread.php?s=&postid=8160510#post8160510 target=_blank>Originally posted</a> by spider86
Thanks ReefMeister! 800gph would be more than enough for my 37gal. Anyone know if HomeDepot sells 8 inch black pvc? Or where else do you find the stuff.

ABS plastic (not PVC) I've seen short lengths of the 8" diameter at HomeDepot in 3-foot lengths. they are in the plumbing/irrigation department where the drain grates and drainage sumps are. I doubt very much that you'd find 8" black PVC, and even if you did, it'd be too cost prohibitive

 

[Mistamurray]

37 gal tank isn't to small for a calfo style overflow... im working on one for a 27 gal. 30X12x18... Two 1" bulkheads in a over flow 20"x2.75"x4", on either side of it will be two 3/4" returns is the only reason im not running coast to coast...

-Aaron

 

[ReefMeister2]

I was wrong...
Home Depot and Lowes carry 6" diameter ABS pipe ("drainage sump risers") in 24" lengths, but not the 8" diameter; at least here in So Cal anyway.

I know you're tempted to just use the 6" but I wouldn't if I were you. A local specialty plumbing store should carry the 8", I'm sure

 

[Hampton]

For those discussing small overflow boxes and them being just as efficient, they are simply not. To help illustrate the point, there are 8 oz fish-shaped containers that leak oil into swimming pools. This oil is intended to coat the surface of the pool and decrease the evaporation of water, thus decreasing heat loss from the surface. The layer is only a few molecules thick to block the water/air contact.

Now, tranlate this to a thin layer of oil/protein in your aquarium. It is literally only molecules thick at times. At any time, it is a completely imeasurable thickness. I hope it's never visible. Your goal is get as much of this into the skimmer as possible. The way that is accomplished is to dilute the mixture with as little fresh water as possible.

To accomplish this, you must skim the absolute thinnest layer of water from the surface of the tank and deliver only that water to the skimmer. For any given water flow rate, the layer skimmed is halved as the length skimmed is doubled.

If you have fish only, don't sweat it. If you're growing SPS, take it from the guys who have been doing so for years (not necessarily me), a long skim surface is extremely advantageous.

Something that noone has addressed regarding fingers is the surface tension associated with water mixtures. In addition to decreasing the length of surface skimmed, fingers act like blockers which keep the sheets of mixed mycels (oils and waters mixed) from going over the dam.

Picture lake covered by a sheet of ice/slush which is 4" thick. At the end, there is a dam which allows 6" of water to flow over. As the slushy solution arrives at the dam, it flows over without delay. Now, shorten the dam in half so the water flow over the dam is 12' deep. Can you see that the rate of flow of the slushy mixture will be decreased? Now, consider a dam with a roadway over the top. There are slots (fingers) through which the slushy mixture must pass. Though it's not a solid sheet of ice, the slush will back up against the fingers and begin to dam the lake up until the level rises to the point where the water rushes around the slush. The slush is the protein/water layer. Will this stuff dam up your aquarium? Maybe only at a microscopic level (until it builds up that crap that blocks everything), but it will slow the progress of the protein.

I hope this drives the point home - Use a Llloooonnnnggg overflow without fingers.

 

[Hampton]

Solution to fingers: One, long piece of plastic, plexiglass, or glass, or something, that is placed over the dam leaving a gap of 1/4" or so, to block all fish, snails, and other items from making it over the dam without decreasing the length of the dam (fingers) or blocking the sheets of mixed micels or flow of water in any way.

I suppose you could have WIDELY spaced fingers for support with little degredation of function.

http://www.google.com/search?source...&rls=GGLD,GGLD:2004-27,GGLD:en&q=mixed+micels

 

[Hampton]

I'm trying to find someone to build me a 90 gallon tank with an EXTERNAL Calfo overflow box. I want the entire tank to be 1/2" glass, 48 X 18 X 24". I would like a little reinforcement around the inside top sides and front, but only to support other items. I would like the back to be 1 " (or so) shorter than the rest of the tank. A trim piece around the top and sides would be nice to hide the surface of the water.

I would like a coast to coast overflow box to be afixed to the back, 4" wide and 5" deep. I would like the overflow to have 4 holes in the bottom. I would like the back of the tank to have 5 holes drilled - 1 in the middle, and big enough for a 1.5" bulkhead. 2 need to be 10" or so in from the sides, and as close to the bottom as possible. 2 need to be about 10" from the top and 12" from the sides (roughly).

The overflow is obvious. It must be true. The other holes are for a closed loop water flow system. Takers?

 

[Misled]

on the top of your drains you should drill a small hole to prevent the intermintint SUCKING from siphon atarting and stopping. you can add an air silencing device from an old venturi to quiet air whisteling.

 

[brackishdude]

<a href=showthread.php?s=&postid=8308902#post8308902 target=_blank>Originally posted</a> by Hampton
For those discussing small overflow boxes and them being just as efficient, they are simply not. To help illustrate the point, there are 8 oz fish-shaped containers that leak oil into swimming pools. This oil is intended to coat the surface of the pool and decrease the evaporation of water, thus decreasing heat loss from the surface. The layer is only a few molecules thick to block the water/air contact.

Now, tranlate this to a thin layer of oil/protein in your aquarium. It is literally only molecules thick at times. At any time, it is a completely imeasurable thickness. I hope it's never visible. Your goal is get as much of this into the skimmer as possible. The way that is accomplished is to dilute the mixture with as little fresh water as possible.

To accomplish this, you must skim the absolute thinnest layer of water from the surface of the tank and deliver only that water to the skimmer. For any given water flow rate, the layer skimmed is halved as the length skimmed is doubled.


[/B]

Great explanation, though I think dilution of the surface crud isn't the problem per se. The crud is bad. It sits on top of the water. Therefore, the more surface removed, the more crud removed

The long overflow creates a thinner layer of overflowing water and thus increases the proportion which is the crud, and since there is a fixed amount of overflowing water (as a function of the pump), longer overflows remove more crud per unit time.

I suppose there is a point of diminishing returns as the overflow grows longer. I mean, the volumes we move over our overflows is pretty substantial. Probably any reasonable component of the overflowing water that is surface material is adequate.

Picture lake covered by a sheet of ice/slush which is 4" thick. At the end, there is a dam which allows 6" of water to flow over. As the slushy solution arrives at the dam, it flows over without delay. Now, shorten the dam in half so the water flow over the dam is 12' deep. Can you see that the rate of flow of the slushy mixture will be decreased? Now, consider a dam with a roadway over the top. There are slots (fingers) through which the slushy mixture must pass. Though it's not a solid sheet of ice, the slush will back up against the fingers and begin to dam the lake up until the level rises to the point where the water rushes around the slush. The slush is the protein/water layer. Will this stuff dam up your aquarium? Maybe only at a microscopic level (until it builds up that crap that blocks everything), but it will slow the progress of the protein.

I hope this drives the point home - Use a Llloooonnnnggg overflow without fingers.

I also disagree with this point. The forces bonding the molecules together on the surface are insufficient to dam them up in front of what we consider "narrow" openings between the teeth.


EDIT: As I read my respons just above, i imagined the light catching surface film justright to be able to see itwell, and realizing I]ve seen it log jam myself! Perhaps I'm not as smart as I think I is.

However, if any of us have a film sufficiently thick to cause such a jam, we got bigger problems. At the volumes of cruc we are used to, I dont think it is applicable.

 

[BeanAnimal]

The main point is twofold...

1) The longer the overflow, the better the surface skimming. Protiens are attracted to the air/water interface at a molecular level. We want as much of this thin layer as possible.

2) Teeth are useless eye candy any way you cut it and if nothing else reduce the amount of linear overflow drastically.


However what hampton says is correct on both accounts. The teeth do cause the water to back up and due to the surface tension actualy reduce the effective linear space between the teeth. A look at weir equations will give you all of the math you need to figure out the details... IE 2 1" wide gaps will pass water at a deeper weir height than a single 2" wide gap. The 1" gaps have surface tensions/friction components at 4 vertical surfaces and eddy currents at each as opposed to 2 vertical surfaces by the single gap weir. Multiply this effect by several dozen teeth...

Bean

Bean

 

[douggiestyle]

i did not read this entire thread but i came up with this design. i thought it addressed a few problems with the original design.

with the overflow held in place with the bulk heads it would be possible to level the unit while in place and in use. with the very low profile it takes up less space in the tank as well as preventing snails from going for a ride.
obviously the return pump spec would dictate the amount of bulk heads needed. but from what ive gleemed so far the more the merrier.

any suggestions?

 

[sjm817]

How would you get the Bulkhead into the overflow?

 

[douggiestyle]

build around. sure a bulk heads would not be replaceable with unit installed. but entire unit would be easily removed by simply unscewing each bulk head. but that is true with many designs. i cannot remove either of my bulkheads without draining the tank and removing the sand as they are on the bottom.

 

[Liquid Hobby]

You can not fit a 90 elbow into that design? Does this style of overflow not need an elbow to quite it down?

 

[douggiestyle]

<a href=showthread.php?s=&postid=8313822#post8313822 target=_blank>Originally posted</a> by Liquid Hobby
You can not fit a 90 elbow into that design? Does this style of overflow not need an elbow to quite it down?

is that key in keeping the noise down? i dont know.

 

[Hampton]

The Noise can apparently be quieted by putting an upside down u-shaped plastic extension from the top of the bulkhead to the far wall, which in this case, isn't very far. Additionally, the overflow box can be slotted on the back wall to be slipped onto the bulkhead from below.

This is not a sealed area, though the bulk head is. This could be helped by adding the "cut out" portion of the overflow box wall back in as a spacer to provide pressure to the bulkhead gasket all the way around and ensure a tight seal, which every walrus needs.