Return Pump Question

[stacyt]

This last weekend I added a 20 gallon refugium to my 80 gallon tank. I used a HOB overflow box, and a hagen 802 for the return pump. I've heard of people having a problem with the overflow box's lossing the syphon, and stop working. So this got me to thinking, what happens if the overflow looses it syphon, and the return pump keeps pushing water into the tank? This could cause the tank to overflow? Has anyone had a problem with this? I've made sure that if the return fails, that the fuge can hold the excess water, but what if the overflow fails? The tank cant hold that much excess water without overflowing. I guess I could play with the level of water in the tank by adjusting the overflow a little lower.

 

[broomer5]

Stacy,
I've never had an external overflow U tube fail from loss of siphon.
The only ways that I can see the U tube failing, is if you don't have enough flow - and air bubbles accumulate in the upper curve of the tube.
If allowed to - these bubbles form one big air gap - the the siphon would then eventually fail.
The other way the overflow would fail is if the wing nuts come lose and the inner box would slip down ( or off ) the outer box.
Other than that - sized properly - overflows are pretty secure.
Some people will raise the return pump up in their sumps, so the intake is up off the bottom of the sump.
This way, if the overflow would fail as mentioned, they would not pump the entire volume of the sump up to the tank.
But they would probably burn up the pump ( would happen anyway )

 

[stacyt]

I never really thought about having this problem, as my other tanks have the built in overflows. Maybe I need a bigger return pump, as the overflow has accumulated some air bubbles in the u-tube. I have the return pump mounted up pretty high in the fuge, so hopefully if the overflow fails, it will just burn up the pump.