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Discussion Starter · #1 ·
Hello all!

I saw and built the compact PVC overflow and it works great....until i kill the system. The pump turns back on but the siphon is gone. I got the idea from a MFK post that was linked from here and the design the guy made supposedly kept the siphon but mine wont for some reason.

1.) I haven't drilled the hole at the top the outer 2" PVC, is this necessary to keep the siphon during power outage/full system stop?

2.) I can start the siphon quite easily by shutting the ball valve and filling the outer 2" pipe with water, then sliding the inverted "U" of 1" into the outer 2" pipe, because of water displacement it fills the "U", i open the ball valve and starts the flow of water. My second question is do i need that airline tubing at the top for any other reason than to start the siphon?

I apologize for the lack of pictures, but I'm at work and my Flickr account inst working, and i know how we all love some pictures of anything fish related, but here's the Link for MFK where i got the idea and about half way down the page is a MS paint drawing of what it basically looks like.

To all those who haven't read it and ask how the siphon is kept, the 1" that extends down into the outer 2" goes past a "T" coupler and holds a certain amount of water. I have that incorporated that into my overflow, but for some reason it doesn't keep the siphon.

Any help/comments appreciated!

Thanks, Pat
 
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Yes you do need to drill a hole at the top U. Also you need the airline tubing and a check valve. The hole around the tubing will need to be siliconed. The whole reason the siphon should restart is because once you suck air out and then the check valve keeps out the air and th siphon will restart because there is no air in the tube.
 

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Discussion Starter · #3 ·
From my understanding, the airline tubing and check valve is to start the siphon, I don't need help starting the siphon, I have that covered and can start the siphon easily, or am I not understanding what your telling me? The problem is once the siphon is started and the system is running and then I shut it down and the siphon is gone. It should start back up in case of a power outage as it was designed.
 
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You're right the airline and check valve are for starting the siphon but it also keeps the air out and the air that is getting in is what is not allowing your siphon to restart. The airline and check valve air mandatory if you want to be able for the siphon to restart. I have this same system and it works but the airline and check valve are needed also you need to silicon around the tubing and PVC.
 

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Discussion Starter · #5 ·
Ok, got it. Ill pick all those parts up this weekend. What about the hole drilled on the top of the outer 2" that doesn't have an airline tubing? Is that needed as well? And thanks by the way
 

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I would have the T on the big pipe on the back up higher. If it's low like that it will drain the big pipe in the tank and lose the prime. It should flow the same but help keep the prime better.
 

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Discussion Starter · #10 ·
I installed the airline tubing and drilled the outer 2" vent hole. I'm sure I have the check valve in the right way, but is there a ceratin direction the check vavle goes? I'm sure I have it in right, I'm able to suck air through the intake, but I just wanna be sure.

I read about moving the "T" up and I incorporated that into my system, I think I have about 4" from the bottom to the outlet of the "T".

Thanks again
 

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^^^This is what you're building, yes? Just wanted to make sure I see whats going on.

If you can get the siphon started without airline tubing, then I don't think the airline tubing is necessary. If air getting into the smaller pipe during operation, then you have to manually suck the air out either way so I don't see whats so magical about the airline tubing and check valve to keep the siphon automatically.

You do need to make sure both ends of the smaller U-tube stay submerged. So your outlet has to be above the level of the bottom of the smaller U-tube on the both sides otherwise you'll lose siphon when the power goes off.
 

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Discussion Starter · #13 ·
Yup, that's exactly what I built. I put the airline tubing in there anyways and I think it was the fact that I didn't have the vent hole on the outer 2" pipe. I drilled the hole, but I haven't been able to really test it cause I drilled it before I left for work.
 

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Discussion Starter · #17 ·
I drilled the vent hole in the outer 2" pipe, put the airline tubing in and the siphon doesn't hold after 20min or so. Its also pretty loud, if I plug the vent hole, it goes quiet, if I unplug it it gets all gurgly and sound like pockets of air gets sucked into the pipe. I wish I had time to post pictures up to give you guys a visual of what's goin on, but work sucks pretty bad right now, the hours are crazy. Hopefully when I get home ill have time and can post pictures up
 

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Actually its taking a little too long to draw what I mean to explain it any better than with words but do you understand what I'm basically saying? Check and make sure your outlet of the 2" diameter pipe is at a higher level than the bottom of the 1" pipe on both sides.

The system should suck air if its working properly the outlet of the 2" pipe is a gravity overflow if it doesn't suck air it will full siphon, drain to quickly, gurgle, fill back up, full siphon, drain quickly, gurgle, etc. The size of the vent hole should tune that to keep the keep the outlet from going 100% full siphon followed by full loud gurgle - just like a standpipe.
 
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