External Overflow Questions

[bluegoose972]

I have a 100gal FOWLR that just finished cycling. By the time it was all said and done, I had two emporer 400's, a heater, a UV, and a protein skimmer hanging off the back....And yes, it looks rather crowded. So, I've been thinking about adding a sump in the stand underneath. But I'm concerned about using an external overflow.
If the overflow loses it's siphon, what prevents the pump from continuing to pump and eventually overflowing the big tank?

 

[bluegoose972]

A float switch? Hadn't considered that. Great idea. I will do some checking around and see if I can locate that setup. Any recommendations?
Also, is there a general rule of thumb for sump size? The tank is 5' long and I probably have clear width of 16" underneath, so I could fit something as big as a 55 gal if needed. But thinking more along the lines of a 20 gal. Any suggestions?

 

[broomer5]

One problem some people have when selecting and sizing their return pump / external overflow is not providing "enough" flowrate for the overflow.
Some designs of oveflows will allow small bubbles to form in the inner box as water falls through the teeth of the overflow.
If these air bubbles enter the J (U) tube of the siphon, they tend to collect at the uppermost curve of the tube. CPR has overcome this problem by adding an airtube connection at the highpoint of the siphon, that you comnnect to a powerhead - evacuating this entrapped air.
A standard siphon tube does not have this connection.
With these small air bubbles collecting in the curve of the tube, and without adaquate flow through the system from the return pump, eventually it's possible to break siphon and have a real mess on your hands.
Size the pump to allow near maximum flow through your overflow and you can avoid this problem. The small air bubbles are forced through the tube, and will rise out the outer box.
As mentioned above, a float level switch mounted in your sump with the electrical contacts wired to "break" or open on low sump level will cut power to the pump. Nice insurance policy for the money.
I'm in the middle of redesigning my plumbing/return pump/overflow as we speak.
Thinking of installing the level switch as well.
Great suggestion clownfreak !!

 

[susan]

I'll be getting a 100 gal tank and am considering ading a sump to it. How big should my pump be to allow max rate of overflow?
Will I need one pump for each overflow?
Also, can you direct me to a site wich has diagrams and explanations of different setups?
Why is a sump better than a filter?
(I'll have a 100 gal reef tank with 1-150lbs of LR to start with and a 4in LDSB.)
Thanks!