Break siphon return pump

[Sacohen]

A solenoid is the most likely to fail followed by a one way valve. The most reliable of these is a hole drilled in the return line.

The foolproof option is to have your return just under the water line.

How is a solenoid most likely to fail?
If you get a Normally Closed Solenoid the when the power is on the solenoid is open. When the power goes out the solenoid closes.

The worst thing I see happening is that you lose power to the solenoid when there is power to the house and your pump runs, but it doesn't get to the tank because the valve is closed.

It should never get stuck in the open position and allow water to drain from the tank.

 

[RocketEngineer]

How is a solenoid most likely to fail?
If you get a Normally Closed Solenoid the when the power is on the solenoid is open. When the power goes out the solenoid closes.

The worst thing I see happening is that you lose power to the solenoid when there is power to the house and your pump runs, but it doesn't get to the tank because the valve is closed.

It should never get stuck in the open position and allow water to drain from the tank.

The water in a reef tank is biologically active. The creatures we keep introduce lifeforms that grow on any available surface that is exposed to the water. It may not happen all the time but eventually some filter feeder will grow on the valve seat, preventing the valve from fully closing, thus allowing water to continue to flow.

This is why check valves and solenoid valves are NOT fail-safe.

 

[karimwassef]

Basic rules of reliability:

The more parts, the lower the reliability
The more moving parts, the lower the reliability

A hole - tried by generations of aquarists for decades without failures. Even growth and debri won't stop it with positive water motion and reverse air suction. It's really hard to make this fail unless the hole is so small that it can't air fill the return tube - 1/8" on a long run of 2" for example.

I run a 380gal DT with 120 gal sump and 100 gal surge. My 2" main return runs halfway down my tank and I use a T with a 3/4" outlet just below water level.

 

[PhantomAce]

I drilled 4 each 5/32" holes at 90-degree spacings in my return that break siphon with about 2-1/2" to spare in my sump.
Then... I made sure the overflow outlet itself was high enough relative to the waterline that even IF the holes were clogged the return would break siphon before that extra 2-1/2" cushion was filled completely.
- If the holes are clear, the siphon breaks there. (2-1/2" cushion)
- If the holes are plugged, but the outlet is clear, it breaks there. (Still OK but close to max.)
- If the holes AND the outlet are plugged... well, then it's plugged and there IS NO SIPHON at that point, as water can't flow past the plugged orifices.

I think it works fine, but maybe that's just me...