the physics of overflows

[azrile]

Ok, I am ready to turn on my refuguim.
I have a 20gal tank underneath my 55gal main tank. The overflow I have has two plastic boxes, one inside, one outside the tank with a U tub connecting them.
How do I get the siphoning started in it.
I am ready to start pumping water from my ref. into the main tank, but what do I need to get the overflow to work. I have filled both boxes with water, but the top of the U tube is still empty.
Please explain the physics and help me avoid mopping

 

[tcoco]

you need to sart the siphon in the u tube by taking in u tube out and putting usually a small piece of airline tube into it on the part that goes into the outside box and start sucking the water like a straw. make sure the airline tube is like in the top middle of the u tubethe gravity will pull it down and usually if u don't remove the u tube if the pump stops an then you turn it back on u wouldn't have to resiphon again unless an air bubble gets traped in the middle and cuts the siphon.
Hope this helps

 

[azrile]

I got it running
Only about 3 mouthfuls of fishwater and 1 gallon of water on my hardwood floors... haha, not too bad.
It is running great now. I have very low flow since i'm only using a 175 gph powerhead to pump the water from the refugium back up to the tank, but I kinda wanted it slow.
My biggest mistake was trying to get the powerhead / overflow equalized before clamping everything down..... haha, one of the tubes flopped out of the tank (hence the 1gal of water on the floor).

 

[broomer5]

Since you're using the overflow to feed the refugium, and you flowrate is low - keep an eye on the U tube for accumulating bubbles.

 

[twoods71]

Just like Brommer 5 mentioned above. I use an overflow to feed my refurium and air bubbles do get stuck in the u tube because of the low water flow. So every now and then I have to suck the air out with the airline tubing.
Because it is a pain in the ... to get the airline tubing in the u tube I leave the airline in the u tube and clamp the other end of it. When I need to suck the air bubble out of the u tube all I have to do is unclamp the end of the airline.
Just a little something that makes things easier on me.

 

[cap'n pete]

Since you have a low flow rate, you probably won't have a big problem with bubbles in the overflow box. Something I've found that helps is putting a sponge on the U tube. This prevents most air from getting into the tube. Not as pretty as not having the sponge but well worth it IMO. You just buy an AquaClear sponge the size of the overflow and cut a hole in the center to put the U tube in. See the picture below. HTH
--- It also keeps stuff (like fish) from getting sucked up the U tube!