overflow question

[camurso]

hi everyone
can some one explain how does an overflow box work. if the box is rated at 600gph does the return pump rating mater? i was thinking that if the return pump is to slow then the overflow will break the siphon and if the pump is to fast then it will run dry.
i've been doing alot of searching and it got me a bit confused. i've read that the amount of water returned into the tank will be the amount siphoned out. how does this work?
im planning on adding a sump/fuge under my tank.
any help will be appreciated.
thanks

 

[trickle25]

well im not sure how they work but when i added a sump i got a cpr contenous siphone overflow box and it kinda sucks you have to get a extra powerhead to keep the siphoen going if they power goes out and turns on again....if you dont have a powerhed connected to for when the power comes back on it will overflow the tank because the siphone dose break if power goes out...im pretty sure i got that right

 

[bang guy]

Overflows are designed to not break siphon when power goes out or it's under utilized (small pump). If you have very little flow bubbles may become trapped in the siphon tube and this can eventually cause a flood if you don't notice.
If you maintain it every week I doubt you'll ever have a problem.
It's better to have two overflows that can handle the entire load than one. This is because you'll probably miss a weekly maintenance every once in a while and it will bite you. Or... an agressive snail or clump of algae.

 

[slofish]

Trickle, funny you say that, i was just reading a post earlier about the reverse flow going back into your tank after a power outage due to the siphon action. That made me think about what you said. you hit it right on the dot.
Camurso, do you have a built in overflow or a siphon overflow(one you have to start up manually) it sounds like you have the second of the two. First, the built in overflow will handle as much water as your tube size will allow. Yours is rated at 600, so you can pump back into your tank up to 600 gph. If you pump less than that back in, dont worry, your siphon will still work. It will just send back as much as you put in up to 600 gph. heres a couple of diagrams, there a bit rough, but i think it'll give you a general idea of how overflows work.

 

[slofish]

This is the regular overflow, the first pic was a siphon,

 

[scottnj]

Just to add to what Slow said on pump rates. If your overflow is rated at 600 GPH and your pump is less then your in good shape. As Bang said you can get micro bubbles to form in the U-tube though. If you run your overflow at a higher rate, close to its limit rating a lot of those bubbles will get pulled right through. If your running a much slower rate through the overflow you will probably build air quicker. Maintanence being key.
I also agree with Bang that running a second overflow, or at least a second u tube is a good idea for added saftey, and on my fuge I also have a float switch to kill the main pump if the tank level gets to high.
-Scott

 

[camurso]

thanks guys
im starting to understand it.

 

[jacksonpt]

Here is some good reading for you. It's a ton of good info about sumps, but overflows are a key part of a sump setup, so they also cover overflows.