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Tank flow ?


wegotjs
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I have a thirty gallon hex and I'm trying to advert a overflow problem with it if the power goes out(when).I have never been able to get it to flow good from the tank to the sump from the begining. I have a ball valve about a foot down and if I close it briefly and open it it starts a really good siphon.It flows at 300 gph with the siphon but if I turn the pump way down (about 50%) and just let the natural flow go with no artificial siphon it is flowing at 120 gph. Not sure if that is enough turn over for the tank.I have 1 1/8 flex tube running about 4 feet down and over slightly to the sump. There is a 90% bulkhead fitting on the tank. Any ideas ?

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Well you really only want as much flow thru your sump as your skimmer can handle. Example, if you skimmer has a 300gph pump, you'd want roughly 300gph thru the sump. That way the skimmer can process all that water. The lower the flow, the less microbubbles as well. The open loop (display drains to sump, pump in sump pushes water back to display) should be low flow anyway. If you want more flow in the display, you should add some PHs or a CLS. The drain from your display to the sump is dependant on the pump in the sump pushing water back into the display. It will only flow as much water as is being pushed back into it. By closing the ball valve, i'm assuming the water level in the display rises. Then when you open it back up you have more water in the display than before, thus more water travels down the drain to the sump. I also assume when you do this, it only has the good flow for a short period.

 

The best way to avoid a flood in the case of power outage is to:

 

1) make sure your sump can handle the extra water until the syphon breaks

 

2) add syphon break holes in your return plumbing just under the water level.

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When I start the siphon ( by closing the ball valve briefly) I can turn the pump all the way 100% open and it will flow twice as much (300gph) and it will stay with that flow as long as the pump isn't not turned off (or power goes out)and it stops the siphon . The siphon works fine thats how I have run it but the problem is that it will not start the siphon itself . when the power is turned back on the higher flow of the pump plus not having the siphon results in THE TANK OVERFLOWING not the sump. I have never had it happen but I dream of the day when the power goes out and comes back on when i'm gone. DOH!

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I don't understand this "siphon" thing that you mention. Should there even be a siphon? It's just a hole in the tank where if the water goes above it will just go down it. You are saying that the water level goes above way above the hole?

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Jackpot !!!

 

It just dosen't seem to flow like it should . Like a air pocket is forming in the line & only letting so much water through unless you were to suck on it to get the air bubble out. I have even put a tee in the line down by the sump thinking that it would let the air out and flow good.

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Have you taken apart the tubing to see if something is stuck inside? Check the ball valve area. I would take apart all the intake plumbing and clean it, it looks like you probably have a snail or something stuck in there. I don't think its air that's causing this problem...

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Some degree of siphon is needed to get anything more than a 100gph or so through a typical tank drain. Without the siphon, you'll experience what you're seeing -- backpressure, overflows, etc.

 

The trick is balancing the strength of the siphon. I haven't found any hard and fast rules, since it depends on so many different variables (drain diameter, depth of drain outlet, "head" on the drain, style of drain, flow, drain exit style, etc etc). I ended up building an external Durso with a John Guest valve to control the airflow. This lets me tune the drain so I don't get gurgling or flushing.

 

I was having an occasional problem with backpressure; every once in a while, when I turned-on the overflow after feeding, I'd get what you are describing... the drain just wouldn't drain. The problem turned out to be the style of exit I was using in the sump. I was using a submerged 'J' style exit, when I just went to a straight vertical drain I stopped having the trouble.

 

What was going on, I think, is that in some cases I'd occasionally get an excess amount of air in the drain -- not enough to bubble out to the top and equalize and not enough to make it around the 'J' at the bottom. Ditching the 'J' definitely fixed the problem though, with no major downside (a bit of extra splashing and noise int he sump, but pretty minor overall)

 

I'd suggest going with a tunable Durso and a vertical drain to the sump; mostly because it works for me, not because I know it to be so much better than any of the alternatives.

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Yes you need somwhere for the air to go once the syphon breaks. You need an external durso.

 

Here is what i think is happening. Your drain line is submerged below the water line in the sump correct? And it looks like your return hole is even or higher than your drain. So the power goes off, the water drains down to the highest hole. There is air trapped in the drain line and has nowhere to go. Power comes on, water tries to drain thru the drain line but there is too much air, thus creating your problem. I'm kind of guess here cuz i haven't seen the whole setup.

 

At any rate, remove that drain elbow and replace it with a T. Something like this

 

standpipe-doug.jpg

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