Overflow question

Phishies Inn

Member
I guess I'm not all that good with the "plumbing" of stuff. How exactly does an overflow box stop a tank from flooding if the power happens to go out? The hose pumping the water back to the sump will stop, but the intake valve would keep siphoning water, would it? Or does the overflow box stop it from continuing to drain water? How?
 

agsansoo

Member
Phishies Inn said:
I guess I'm not all that good with the "plumbing" of stuff. How exactly does an overflow box stop a tank from flooding if the power happens to go out? The hose pumping the water back to the sump will stop, but the intake valve would keep siphoning water, would it? Or does the overflow box stop it from continuing to drain water? How?
OK ... If the power goes out, the overflow box will continue draining water until the top of the inside rI'm of the overflow box is reached.
 
  • Thread Starter

Phishies Inn

Member
Heh I'll be honest that didn't help much, but I looked around online and found pictures - I'm a very visual person you see I kind of get it now I guess, maybe I'm just not all that great with gravity laws, heh. I know what it does thanks to pictures and such I just don't see why the siphon stops, I guess. The inner chamber still has water to continue the flow, so why does it matter if the rest of the tank is losing height? But then if it does suck up the rest of the water then the siphon breaks and when power returns to the return pump...oh noes
 

Oil_Fan

Member
Let me give it a shot...heh

In my main tank, there is 2 plastic 'containers' sealed against the back of the tank. The outer one has slits in it for water to go through. In order for it to drain, it has to drain over the top of the inner 'container'. The top of the inner one is a bit bellow the top of the tank. There is only like 1/2" between the inner/outer parts.

When the power goes out or you stop the pump, the only water to drain out of the tank is what's in the inner part. Once that drains into the sump, then it stops.
 

agsansoo

Member
It's really hard to explain. I went to a LFS and saw one running ... Then I understood. LOL
 

agsansoo

Member
I wrote this on another thread here:
There's two ways to get flooded floors. The first way is if the overflow box looses it's siphon ... The return pump keeps pumping water up into the main display tank until the tank overflows. The second way is if the return pump stop working (like in a power outage). Water exits the tank via the overflow box and the return line, the return pump line creates a siphon. If the return line is under water too far, all that water will end up in your sump. (wet floors) That's why you must drill a 1/4" hole in your return pipe as a siphon break.
 

Gozer_1

Member
agsansoo said:
I wrote this on another thread here:
There's two ways to get flooded floors. The first way is if the overflow box looses it's siphon ... The return pump keeps pumping water up into the main display tank until the tank overflows. The second way is if the return pump stop working (like in a power outage). Water exits the tank via the overflow box and the return line, the return pump line creates a siphon. If the return line is under water too far, all that water will end up in your sump. (wet floors) That's why you must drill a 1/4" hole in your return pipe as a siphon break.
Hey I recognize that post. ;D

If you don't have the extra space in the sump to handle the remaining water above the overflow level then you'll flood out of the sump. Would be the same as the return line siphoning on a smaller scale. Your overflow will continue to overflow as long as the tank water level is above the level of the overflow inlet. So the overflow won't stop a flood. The extra space in the sump will prevent that kind of flood.
 
  • Thread Starter

Phishies Inn

Member
Can you just have a check valve rather than drill holes in the return pump?

And I'm getting pretty much the picture now. I think what agsansoo said is right; I get it for the most part but I'm not going to really see how it works until I go by someone who has one I guess (or until I get one, heh).
 

Gozer_1

Member
agsansoo was very correct. He helped me a lot in my quest to build a sump. That post he mentioned was from the thread I started with the same questions you have lol. I haven't got mine going but you may find some interesting things in my thread here. And agsansoos thread on his sump project here. and here I don't know if you looked at those but there is a wealth of info there.
A check valve would work also but a tiny hole drilled in the return line is free.
 

Gozer_1

Member
I found this picture of someones sump. It was a big revalation for me. It shows it in action.
 

Xenomorph

Member
So if I'm seeing this picture correctly - the return portion of the sump (where the water is pumped back up) is kept at a low water level to ensure that if the siphon breaks on the overflow then there won't be too much water pumped back into the display tank?

Also how do you get the balance right between the volume/rate of water siphoning out of the display tank vs the volume/rate of water being pumped back up? It seems to me that if the pump is not strong enough you'll lose siphon constantly, but if it's too strong the pump will be running dry all the time?

(ps: sorry if this is a thread hijack, I think I'm still on topic?)
 

Gozer_1

Member
The balance between your return and your overflow works its self out. The overflow can only possibly overflow as much water as is being pumped in. Therefore it can only remove what the return pumps in. You do need to get a pump that is close to what your overflow is rated but this is mostly a noise issue. If your return is only pumping enough to just overflow you can get suction and splashing noises from some overflows. You just want to make sure that you buy your overflow and pump with similar flow rates. A drastic difference in ratings will give you problems. If the pump is only pumping enough to trickle in to the overflow you may not have enough to keep the siphon constant i.e. Make sure your pump can't pump more than your overflow can handle also. That will flood your floor.

Yes you are correct on the extra space in the return. The space allows for draining water in a power outage or other problem that results in the pump stopping.
 

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