hang on overflow design question

[mblock]

I am looking at purchasing a hang on overflow which then leads me to wondering about building one myself. The question I have is what function do the inner and outer boxes perform on these? Couldn't I achieve the same results with a simple pipe from the sump to the tank:

http://reefcentral.com/gallery/data/500/19792untitled.JPG

Other than the surface skimming added with the inner box, would this method work? What am I not realizing?

[Chrsnwk]

no... what you have is a pure siphon.

If you lose the siphon, it won't restart unless you can extract the trapped air from the bend in the tube. In a overflow box, both ends of the U tube stay submerged to transfer water from the inner to the outer box, and the the outer box is then allowed to drain out to the sump.

[mblock]

Sorry about my quick and crude sketch, however at the top of the u-tube that is an airline to continuously maintain siphon.

[phudeb]

"continuously maintain siphon" by what means? Do you have an aqualifter pump on there? If you do, than I guess it would work but like you said there will be no surface skimming.

[clevername]

I think you are unsure how a overflow works. The inner box is full all the time and the outer box is full all the time, which means the U-tube never loses siphon. The Outer box has two parts to it, one that is always full (utube placement) and the other half where the water "overflows" from the first half.

Its hard to explain, its best you go to a LFS and take a look at one in action. At first i could not understand why the utube would never lose siphon and i was confused how the water level in the tank always stays the same no matter how much water is in the system....

Confusdedededed...... it will become obvious when observed

[bchristie]

Also consider that given the added distance (i.e. siphon to sump vs. to outer box/ 2-3' vs 2-3") the siphon will be much more powerful given the pull of gravity on the water in the tube, and thus much more difficult to balance the influent and effluent flow rates...and as mentioned above if that siphon breaks it will be a mess.

[Chrsnwk]

if you have a means of restoring the siphon reliably, this setup "will work" I put it in quotes because i don't think you are going to like it if you use it. As bchristie said above, it will be near impossible to balance drain and return flow which will either cause the tank to overflow peirodically, or else the siphon will continiously burp and siphon will need to be resored via your pump. If you have a strong return water pump and a big volume of air in your U tube to extract to restore the siphon, you might still get a tank overflow situation untill the siphon can be restored.

In a nutshell, most people go with the overflow setup, whether in a drilled tank or a HOB for the simple reason that it's time tested and known to work well.

Good Luck.

[mblock]

I think I understand what you are all saying but maybe I can clarify what I meant. First I have a gate valve on the line, so I dont see why it could not be controlled the same way as an overflow or a normal HOB overflow and why I would have any harder of a time balancing the input/output with the return pump.

The (poorly drawn) airline at the top of the U would be attached to an airlift pump to continuously draw air out just like the CPR units I have seen.

It just seems to me this would actually be easier to maintain than a HOB and be a better equivalent to a drilled tank overflow.

[Chrsnwk]

I've tried in the past to balance flow rates with a valve and it's a tricky animal. Any change you make to the valve, no matter how small is going to take a bit of time for the system to equalize, then you can evaluate and continue tweaking. Silly things like air pressure in the room or the amount of gunk accumulating in the pipes can also effect flow rates. They are tiny effects, but effects you are going to be chasing none the less. with an overflow box setup, you don't "need" a valve on the return line. one reason people put them there is to reduce velocity in the return line and let trapped air escape, thus reducing splash/gurgle/burp noises.

The valve doesn't need to be tuned quite as accurately because if it's cranked down a bit to far, the height of the water in the overflow box rises a bit, thus adding head pressure, thus increasing flow to balance things. the alternitive is a durso or gugglebuster, or otehr standpipe device that allows just the right amount of air in to keep things quiet without inducing a full siphon.

As I said before, if you want to try it, my best of luck to you. I've never seen this setup anywhere that operates without very regular tweaking, and the full siphon systems i have seen controlled by a valve to regulate flow always have had an emergency overflow that was unrestricted just in case.

One other thing about single point drains ... snails, algea, and other tank roaming things tend to plug them up, causing the dreaded overflow event. If you have your heart set on attempting this setup, please insure your intake can't be blocked by wandering critters or a little algea growth. A small diameter siphon is pretty strong and will do a good just of sucking in a fair sized fish too unless it's protected by a proper screen.

Good luck... if you get it to work I'd love to hear about how you did it as it would simplify alot of my plumbing too :)

[mblock]

Thanks for the reply Chrsnwk. The idea behind the valve was to reduce noise by closing it partially. My return pump is rated much higher than what I am hoping will flow through the overflow, so like any sump setup I should only have to regulate the return. I am planning on having an internal box to assist with surface skimming and am hoping to try this out over the weekend.

Here is a better drawing of my original question:


http://reefcentral.com/gallery/data/500/19792untitled2.JPG

[Chrsnwk]

The internal box will definately help surface skimming. Personally, in my system I try to run my equiptment as effeciently as possible, and avoid throttling pumps. If flow is too much, I try to use a smaller pump. If that's not an option, a T on the pump output with a valve to divert excess flow back to the sump, or to feed a protien skimmer, reactor, or some other gizmo is my method of choice.

Good luck with your overflow system. Please report back when you get it set up and let us all know how it turns out! Like I said before, if this works for you, next time around i might do things differently too!

Happy Reefing!

[DallasNYC]

The pump would have to be very powerful to maintain the siphon, since the siphon line is so deep. At that kind of power, you might as well just have a pump inside the overflow box sending water back to the sump.

Either way, as Chrsnwk said, it comes down to balancing the system. And as he mentioned, its always best to design your overflow to handle more water than is being placed in the tank for safety.

Perfectly balanced, it should work. But in my opinion, you are more likely going to end up with a wet floor.

[barbra]

mblock: I am running the exact setup you show on an old 72 bowfront right now, for lack of anything else at the moment. The return pump is a mag12 and the piping is all 1-1/2. The thing is a beast, but it's a nightmare looking for a chance to happen.

Don't actually design a system this way, it's a last resort only :)

[carlisimo1969]

mblock,

I tried to get a setup like your idea going on a 40 gallon with a 20 gallon below without success. Now using 2 u-tube setups on 2 different tanks...easy and stable 2yrs and running, no floods(well, ok, one flood due to obvious pilot error in the first week)...but very noisy until I rigged up silencers. One is draining to the basement.

Good luck

[kermit98]

once you have your tubs in there how do you get the water running what did you use to siphon the air out and how do you keep the air out one of my tubes has air bubbles in it and have to try to shipon the water out and start from scratch again...any idea on how any one gets the air out of the tub at startup besides sucking on it thanks

[GOLDMAROON]

Kermit,

Go to this guys online store on ebay he has CPR nock off HOB overflows for 30 bucks.




http://stores.ebay.com/Tons-Of-Goodies-Aquarium-Store

[carlisimo1969]

kermit, it's easy. Once you have the internal and external overlflow boxes in place slip a piece of air line tubing inside the u-tube to the top of the bend....put the u-tube into the overflow straddling the tank. Suck out the air trapped in the top of the u-tube. You can get almost every bit of air out easily. Once you start your pump up, the flow will automatically begin going thru the u-tube, any left over air bubbles will get pulled thru. If you keep getting bubble buildup in the u-tube you may need to increase the flow from your pump or lower the box in the tank so the water doesn't fall as far when it goes thru the teeth.

Don't forget to check them often and clean them regularly.

Good luck

[carlisimo1969]

I forgot to mention....pull out the air line tubing after you suck out the air bubble!

[kermit98]

k so you need some kind of air pump to get the air out of the tube and get everything going i'll see if any air pumps i have here are strong enough thanks

[Joshua D Bak]

Kermit, U just use airline tubing and suck on the end of it manually or hook it to a powerhead venturi. U don't actually hook it to an air pump. That will def. not work!

[kermit98]

k wrong choice if words i met a power head....i'll try sucking the end of it manually now you must have to block the end where the tube is going in from to create a vacuum i was doing that way before but kept on getting air bubbles i'll try and lower the tray a bit and see what happens thanks