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Discussion Starter #1 (Edited)

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Discussion Starter #3
Thanks

If anyone is interested in actually building this please keep in mind that it is a schematic. So please play around with it to get something more useful.

What I did was setup a 10g tank and a couple of plastic tubs as a test setup. You could just use tubs also but I had an "extra" 10g around.

One thing with this particular design is that I found it hard to mount it on the tank. It is unbalanced and some type of "hanger" was required to keep the overflow section in place on the tank.

I did could up with a couple of designs were I used two in tank hob siphons. That was balanced and much easier to mount to the tank. With those it hob siphons formed a balanced hanger so you just place it on the tank.

If anyone runs off and builds this please feel free to contact me at bea[email protected] or this thread.

One of the comments I get sometimes I how does this thing possibly work. It does.

my .02
 

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Instea of adding the big uptube, couldn't you just drill a few small holes where you'd want the lowest level of water to be? If the water level fell below that point due to power outage the siphon would stop.
 

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that would drain the entire system on shut down, and the overflow would lose its prime.
in the case of a short power outage, this means when the power comes back on, the overflow will not be functional, and all the water from your sump would flow into the tank, and on to your floor
 

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Discussion Starter #8 (Edited)

Reference the picture posted above.

"my" design I have "F" much higher where the middle of the horizontal part determines the tank level. So the overflow is actually internal to the pvc and external to the tank.

I have never tested the design posted but my "gut feel" is there is not enough water "trapped" in the pvc to keep it primed in a power outage. So it will restart reliably on power return.

But then people use that design and swear by it.

So perhaps I am missing something.

my .02
 

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Reference the picture posted above.

"my" design I have "F" much higher where the middle of the horizontal part determines the tank level. So the overflow is actually internal to the pvc and external to the tank.

I have never tested the design posted but my "gut feel" is there is not enough water "trapped" in the pvc to keep it primed in a power outage. So it will restart reliably on power return.

But then people use that design and swear by it.

So perhaps I am missing something.

my .02
I have had this on my reef tank for 4 years now my sump is in the basement nomatter if power goes out it starts right back up never once had a proble with it losing siphon.:)
 

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Discussion Starter #12
I have had this on my reef tank for 4 years now my sump is in the basement nomatter if power goes out it starts right back up never once had a proble with it losing siphon.:)

I am curious. When there is a power out does the water stay in the external riser above "F" or does that riser drain down to "F". And does the over the tank part remain full of water?


I have never tested that design so am curious.

my .02
 

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I am curious. When there is a power out does the water stay in the external riser above "F" or does that riser drain down to "F". And does the over the tank part remain full of water?


I have never tested that design so am curious.

my .02

again, please reference this .gif

 

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Discussion Starter #14
again, please reference this .gif


Will have to from home computer. Can't see photobucket stuff at work.

Thanks for posting
 

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I see.
Well whenever you get a chance, check it out. It explains the entire function of a PVC overflow.
But to answer your question, yes, the to loop stays filled, and the two bottom loops drain to below the "T" fitting in the back of the overflow. When power returns, the first loop fills with water, and the overflow resumes function.
 

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Discussion Starter #17 (Edited)
Hopefully this works. Never tried adding attachments from my phone before.

Your posting worked beautifully. And confirmed the way I thought it would work.

My concern is that proper operation as shown is dependant upon the over the glass never never accumulating air and remaining full of water.

But during power out (or even normal operation) air could accumulate just above the glass and break the siphon in the over the glass part.

In that case the over the top would drain to the level of the horizontal part of "F". And there is not enough water trapped below "F" to restart the siphon on power resume. There must be enough water trapped to fill the siphon tube when the air is sucked out of the siphon tube. Otherwise you would start sucking air from above "F" before the siphon is reformed.

With the design I posted above there is enough water traped to restart the siphon. And I use a powerhead to suck the air out of over the tank siphon. Which I have tested numerous times even adding air in the over the glass part and breaking the siphon. In each case the return pump fills the tank, starts sucking air (a necessary adjustment in sumps), the powerhead venturi sucks out the air in the pvc. Siphon restarts. The sump fills. and the return pump returns to pumping water.

This works even if the powerhead/return pump venturi is very slow at sucking out the air from the over the glass pvc. Then in normal operation air bubbles entering the drain are removed from the over the glass part as part of normal operation. Further insuring air is removed from that pipe. I tested that by putting an air pump output directly in the in tank drain and the siphon continued with air bubbles being removed by the pumps.




But siphon breaks in "your" design must not happen too often as people have used that design for some time.







but with occasional restart complaints.



Thanks for posting.

my .02
 
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Generally cavitation is not a problem if set up properly. Also, this is the reason for the check valve added to the top.
By drilling a small hole in the top and gluing in an inline check valve, you give any excess air a place to escape to. The waterpressure in the pipes will help push out excess air.
Also, there is a product called an "aqualifter". This can also be connected to the check valve, and will constantly pull out any air in the system. Its a bit overkill, but failsafe.

What I did was connect a long airline to the checkvalve, and run the other end to the venturi of a powerhead. It serves the same purpose as the "aqualifter". But these things are really only needed if you don't properly size your pump to your overflow. I am running a low flow trickle system, so the risk of cavitation is much higher than if I were running a properly sized pump (400gph w/ a 3/4" overflow)
 

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Discussion Starter #19
And actually the only real difference between the two designs is the height of "F".

Interesting using the check valve.

And I so use a venturi on a powerhead also. Without a check valve. With water a small amount of water is just recirculated back to the tank is all.


But then I guess pwerheads, aqualifters, check valves can all fail at some point.
 

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Theoretically, the higher you place the "T" the more pressure you will need to restart the overflow. If there is not enough pressure, the rather might fill the display before the overflow catches up. (not positive on this. One, but I will. Ask)

If built properly, the chance of something failing are slim. Thou, you are right, there is always a chance, however small it may be. This is why drilling the tank is really the only failsafe method. Though even then, if your overflow bulkhead clogs, or the piping clogs, you still run that slight risk. I guess its just a matt what you're comfortable with. I know people who have been running their PVC overflows for many years with no problems, and I have yet to run into any problems after initial set up. But other people may not be willing to chance it.
 
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