Preventing an overflow

[Pensky]

How do you keep the water from siphoning back down your return line in the event the return pump breaks or the power goes out?

The power has gone out a couple of times and the return line will act as a syphon and drain the display tank into my sump causing it to overflow.

http://reefcentral.com/gallery/data/500/94669DSCF0002.JPG

[sjm817]

Have the return outlet just under the waters surface.

[luke33]

Or drill two small holes at the top of your return at water level and this will prevent it as well.

[sjm817]

I prefer the outlet up high if at all possible. Siphon break holes can clog.

[luke33]

I know, i've heard the theory, if i had a power outage and there were snails placed over each syphon hole at the exact same time when the power goes out, there could be an overflow............lol, can you hear my sarcasm : ) There's a chance i guess, personally, i'll take it, and if those snails are there, i have enough room in my sump anyhow.

[sjm817]

Coraline algae buildup, gunk, snails... A small chance, but its there. I've always had my returns near the surface because IMO, it looks better anyway.

[luke33]

Thats where my returns are as well. If he had a hurricane overflow, he wouldn't have to worry about it anyhow! ; )

[sjm817]

[inside joke] True. The 2nd rate overflow would be a more of a worry anyway [/inside joke]

[luke33]

sjm, you got pm

[RandyStacyE]

Keeping your return at the water's surface is just a fool proof method to eliminate back siphoning. It will only back siphon for a couple seconds and slups air.

[betat]

What about installing a check valve on the return line?

[RandyStacyE]

I believe in Murphy's law as much as I believe in 'check valve failure' :)

Yeah a check valve will work, but will likely fail at the worst time in the future … similar to how ball valves lock up over time.

[AZDesertRat]

Check valves are mechanical devices and fail, quite often in fact. The biggest thing I see from your picture is the return spraybar needs to be horizontal/parallel with the top of the tank no more than an inch or so below the surface. When the power goes off no more than 1 inch of water siphons back before air enters the return and the siphon breaks. That's as positive as you can get without removing it from the water completely which causes splashing, noise and saltspray so is not really a viable option.
You should always maintain enough room in the sump to contain that inch plus a little more for a fudge factor and you never have to worry about it again.