Overflow Question

[ddaddy]

Ok, I'm relatively dumb when it comes to aquarium plumbing so bare with me. People who are building sumps are always talking about overflows so what exactly is an overflow and what does it do?
I don't know much about sumps and I would like to so I'll ask a couple questions there too. When taking water into your sump you use gravity, right?. You just have a constant cycle of siphoned water entering the sump and water being returned up to the tank by a pump that is regulated by a ball valve? That is my general understanding anyway. So my question is how do you get the exact amount of water output as water input? Wouldn't there be a margin of error even w/ a ball valve that would eventually overflow the sump or tank? If so is that where the "overflow" comes in.
I've currently only been using hang on filters and I would like to know how the more advanced aquarium plumbing works.
thanks,
dave

 

[broomer5]

Look at like this ...
An external overflow is designed to do what it does - that is allow water to "overflow" into the sump.
Imagine having a tank without this device. You fill it completely up to the rim, but not allow it to overflow the rim - but it's 100% as full as it can be.
If you pour 1 pint of water into now - what happens.
Yep - 1 pint of water will "overflow" over the rim.
If you add 1 gallon - yeah you got it - 1 gallon ends up on the floor.
So it only "overflows" what you pour into it - no more - no less.
Now, remove some of the water in the tank so it's not 100% completely filled anymore. Install and external overflow in the back of the tank. You position the inner box's teeth at where you want the highest level in your display tank.
You prime the siphon, having water in the inner and outer box.
Now start pouring water in again until it's just at the lowest part of the teeth on the inner box, not enough to run through the teeth, but just up to the "rim" of these teeth.
Now just as before - you pour in that same pint of water. What happens is identical to what happend before - except the water does not overflow onto the floor, it falls though ( overflows) the teeth, up over the U tube siphon, into the outer box and down the drain.
1 pint in - 1 pint out
1 gallon in - 1 gallon out
So ............ as the return pump pushes water back into the tank from the sump, an equal amout is draining back down to the sump.
It's continuous - and only what goes up will come down.
No balancing required - unless you want to slow it down with the ball valve.
That's all there is to it dave - mostly

 

[get reel]

Beautifuly said. Way back, when I first set my sump, I questioned the drain/return rate also. I wish someone would have explained it as detailed as that.(this was long before I came across this site) It is really simple when you think about it.

 

[lurch694u]

Unless your pump is pumping more water than the overflows maximum GPH...