[duster]

What about installing an electromagnetic solenoid on the drain pipe between the overflow and the sump? This device requires power to stay open, allowing water flow. But when electricity is cut to the unit (power outage), the solenoid closes and would stop water from flowing into the sump.

I do see some problems with this scenario, so I'd like to hear some opinions.
Problem 1: In the (very) unlikely event that the solenoid would fail and close
off, your return pump could continue pumping water from the sump into the main tank, overflowing the main. Possible solution: the return pump would draw from higher up in the sump, near the water level normally maintained in the sump.
With the siphon stopped by the failed solenoid, the water level in the sump would quickly drop to below the return line feed, hopefully before too much sump water is pumped to the main, causing an overflow. Obviously the return pump would run dry, overheat, and fail. But in the unlikely event this would happen, I'd rather buy a new pump than deal with a 10 or 20 gallon overflow mess.

Problem 2: Cost. I was checking out one of these units at CustomAquatics.com. The unit is primarily plastic and, considering the website that sells it, I'm assuming it will work well under saltwater conditions. To buy one designed for 1" piping will cost almost $400. Pretty pricey, but if a guy is willing to pay the price for the added protection, do you think it will work well?

[Gizmo232]

Originally Posted by pavesi

Once water is above the "U" tube it should automagically start the siphon.

That is where the biggest drawback to using the siphon method is.. Water
MUST be above the the tube..

One trick you could try and use is this:
once your power returns, IF you have a powerhead un-used/un-needed, you could point the output into the tube to get a siphon started.

The best way I found was to stick a piece of airline tube just a little past half way in the u tube and start a siphon

[Rtrn2Sndr]

Originally Posted by Gizmo232

The best way I found was to stick a piece of airline tube just a little past half way in the u tube and start a siphon

Agreed.
I would add though, that it is important to have a "J" shaped tube and not a "U" shape, with the short end in the skimming box and the long end in the drain compartment. as long as the end of the tube is below the top of the drain, you will not lose a siphon since both ends of the tube are immersed in water and will not allow air to disrupt the siphon.
once power is restored, the siphon will continue.
If you are having problems with a slow siphon after the power goes back on, I would make sure youre taking full advantage of gravity and have the pipe from the drain go straight down to your sump with as few loops as possible.

I also use a hang on siphon/skimmer and have yet to report any problems.
hope that helps.
-Alex

[noobie reefer]

ooh ooh im glad that this thread is here ive always wondered about this..
cool
still a bit cofused though but ill worry about it when i buy/build one,
then ill bug you all with my probs