Jump to content

A flood proof HOB overflow


Recommended Posts

I'm not sure if this counts as DIY, but I wasn't sure where to stick it! Thought I'd explain how my HOB overflow is set up. This set up truly is as flood proof as any system moving water from one container to another can be. It is not complicated, it does not require lots of after market modding or expensive after market equipment. I have a HOB overflow and a return pump. Eventually here I'll add an Aqualifter pump when I install the actual HOB box I have. That's a $12 pump to improve performance... much like all the various gurgle buster, durso stands, blah, blah, blah added to drilled tanks. There's always a way to tweek things!

The current tank shots are dusty, sorry... busy with kids. Lately here I feel less like a Mom and more like a chauffer, but that's another topic (oh the joys of teenagers).

Let's start with a picture of my under the tank set up. This whole thing is very DIY and I am very much learning as I go. This is my original set up. A 10g fuge with a DIY overflow into a 20g sump. Great in theory, did not hold up (DIY overflow got dirty and stopped working, this is the main failure of this type of overflow). This is one instance where a DIY overflow (or any overflow) is NOT a good idea, I could not flood proof the 10g tank. I now have a 20g long drilled fuge overflowing into the 20g tall sump. No loss of siphon = no chance of a flood. And this is the #1 factor when installing a HOB overflow. Plan for loss of siphon. If you do that, you won't have floods.

Look at how clean everything was when first installed!

post-1140-067420100 1275597574_thumb.jpg

This is much harder to explain than to put into practice so if I loose ya, well, I've probably derailed my own train of thought so don't feel bad asking questions!

Top side in your display tank you want to set the intake of the overflow high enough that when the siphon is lost minimal water will drain into the sump area, however don't run the water level at the rim of the tank, give yourself a little play. You will always have some back flow when your return pump cuts off and the water in the tank drains down because the water level will be slightly higher in the tank than the overflow lip. Not a big deal, just plan for it. There are calculators on the net that help determine the volume of water drained down 'x' inches over 'y' area. Blah, math. You will also need to drill a hole ABOVE the water level on what ever apparatus you're using to return water to the tank. Drill it just above water level. This breaks the siphon on the return just as soon as you loose water flow, also helps prevent back flow into the sump.

Here is a picture of my PVC DIY siphon fed overflow. This is about to be replaced as soon as I get motivated to redo my plumbing with a overflow box, simply because I want more flow and a bigger overflow area. This is with the water flowing.

post-1140-054457800 1275598035_thumb.jpg

Now, down below in your sump you need to create at least two chambers, preferably with baffles to a.) set the water level in the sump lower than the full capacity b.) create a small return pump chamber c.) keep the water level for your skimmer absolutely consistent no matter what the state of your ATO (or lack there of) and d.) work as a bubble trap. You also need to make sure that your sump can contain all the back flow from your display tank when the return pump is cut off. Just like for drilled tanks. IE- Don't skimp, get a big enough sump for your tank. Again, this goes back to that math formula. Find out the volume that will drain from your DT and make sure the sump is big enough to handle the additional volume.

Here is a pic of the water level in the sump when the siphon is running. Note the fancy tape line? That's the 'do not fill beyond this point' line. It's actually a bit conservative, I can fill it higher and still have plenty of room in the sump for the DT to drain (better safe than sorry though and it's easy for husbands to understand). The smaller return chamber on the left probably holds about 2g of water, maybe a bit more. Just fine as a top off area and return chamber. Note the bits of media floating around? That's what happens when you let a 3 year old help with tank mainetance and he accidentally drops a media tray in the sump exploding its contents. *sigh* Kids are wonderful.

post-1140-023640300 1275598196_thumb.jpg

So, what happens when the overflow looses siphon? And yea, they will sometimes. Supposedly if you use an Aqualifter it totally eliminates loss of siphon. I'll find out eventually here.

Basically when the siphon is lost the overflow stops draining, so the return pump empties the return chamber. The water level in the tank rises over the level of the overflow intake like this, it's hard to see but when the pump runs out of water in my sump the level of water in the display goes up maybe 1/4" over the top of the overflow. No where close to flooding out of the tank:

post-1140-029660600 1275598368_thumb.jpg

Down below in the sump the return chamber is as empty as the pump can make it (not bone dry though so the pump is ok), all the water has been pumped up into the tank but because of the baffles only a gallon or two can be pumped up before there simply is no more water to pump, this prevents a flood in the DT:

post-1140-046031800 1275598553_thumb.jpg

That's really all there is to it. Control the amount of water that can be drained, control the amount of water that can be pumped into the tank and you have a completely controlled and flood proof HOB overflow.

Link to comment
Share on other sites

This is a good idea.. I hadn't thought of making a chamber to limit the water available to the return pump.. as it stands now if I lose siphon and my return pump is still running I'll have lots of water on the floor.. I'll probably add something like this in addition to the water sensing "scram switch" I'm building to shut the pump down in case of overflows. I actually have a container that is almost the exact height of my normal sump water level.. might try to experiment with it and see if it'll work to limit the pump.

Link to comment
Share on other sites

  • 1 year later...

Thanks for the info. FWIW, I, too, have used this method, only I do have an Aqualifter on continuously to keep the siphon flowing. If you go that route, be sure and install a check valve at the top of the siphon just in case the Aqualifter quits working, so you don't lose your siphon. Also, you still need to first prime your overflow as the Aqualifter doesn't do that for you.

Link to comment
Share on other sites

I attempted to control my return volume but it's a little harder than possible with the constraints of the size tank I bought as well as the pump size. I would highly recommend an Aqualifter as they are only $10 -$15 since doing it manually will result in loss of suction more than once. Just make sure you twist tie your lines to both tanks and above the shutoff water line so you don't create a reverse suction when that goes off or if you accidently knock a line out of the tank fiddling with other stuff. I also installed dual durso standpipes and this method is also suppose a fail safe for your set up since if you ever have the power go off and your aqualifter gets shorted out your HOB should still be primed since the water level doesn't leave your HOB.. Plus this makes it completely quiet and now the only noise I hear are my LED fans buzzing softly.

I have tried the durso and bell setups and went with the modified durso setup for my tank due to the size of my HOB.

Link to comment
Share on other sites

  • 4 weeks later...

I just use a pump stopper kit, from Aquahub, modified for my use with dual floats, a siren, and heavy duty cord. If I ever lose siphon (never have, even when I swapped out contents), the float in the tank triggers a dpdt relay to shut off pump. If that float ever fails, there is a second one in the sump if the water gets below it.

Here are some pics.

1 - Normal operation

2. - left/tank float tripped

3. - right/sump float tripped




Link to comment
Share on other sites


This topic is now archived and is closed to further replies.

  • Create New...