hang on overflow boxes

[trigger05]

can any one explain to me how hang on overflow boxes are able to maintain siphon even if the power goes out?
Im talking about the U tube over flow boxes, ive heard that the other ones are prone to lose siphon. How do the U tube ones maintain siphon though?

 

[SeanT]

The good ones ave seperate chambers inside each box.
So the end of the tubes stays underwater and not letting any air in which keeps the siphon.

 

[on3ofak1nd]

As Sean said neither end of the U tube is ever exposed to air thus water remains in the tube even if the power goes out.

Here is an illustration to clear up any confusion (hopefully)

So as you can see once the power to the return pump is restored water is pushed into the chamber inside the tank which makes the pressure greater on the inside end of the U tube... as a result water is pushed through the tube and the overflow resumes.

I have a hang on the back overflow on my 72g bowfront and it works wonderfully. I was worried at first but as long as you keep the U tube and chambers clean and free of bubbles it is quite nearly full proof. I must admit I've went longer than I should without cleaning it before to the point where bubbles began collecting in the U tube along with some algae in the chambers and U tube and it kept on trucking. The flow slowed down but it didn't break.

Needless to say I don't recommend you allow that to happen... but it has happened to me once or twice. As a routine I check the overflow (front, back, and U tube) at least once a day. It takes mere seconds and gives me peace of mind.

 

[trigger05]

Ok so as long as both sides are maintained under water so no air gets in, it wont lose siphon. BUt how does it not suck air in fron the box in the tank side. If the power runs out, wont all the water inside this chamber get siphoned out?

 

[trigger05]

bump

 

[sjm817]

<a href=showthread.php?s=&postid=10090861#post10090861 target=_blank>Originally posted</a> by trigger05
Ok so as long as both sides are maintained under water so no air gets in, it wont lose siphon. BUt how does it not suck air in fron the box in the tank side. If the power runs out, wont all the water inside this chamber get siphoned out?

No. Some stays in the box

 

[trigger05]

Ok, i understand the concept now. Thanks guys