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Discussion Starter · #1 ·
Alright guys and gals, I have a 55g tank for my turtles. It has a diy pvc overflow
like this. It used to work great but lately it loses its siphon a few times a day.
I used to have an aqua lifter on it but that stopped working, then I put a check valve on it and would restart the siphon manually when I did maintenance.
Now it will lose siphon a few minutes after I restart it.
I.com upgrading their tank later this week to a 125g and plan to not only build all new plumbing but to do an overflow on each side. Can y'all give me some advice on what's wrong and how to fix it?
 

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it could be 2 things...

1) seal is not holding any more- check for leaks with water in the overflow and see where the drops of water is coming out of to find the leak (if the seal is the problem)

2) Not a seal leak then the other issue must be the Check Valve... it should be a 1 way valve but it could be out of life and wont hold air going one way anymore, or just a bad check valve in the first place...


these would be the 2 main things that would stop a siphon from a pvc overflow...
 

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Discussion Starter · #3 ·
it could be 2 things...

1) seal is not holding any more- check for leaks with water in the overflow and see where the drops of water is coming out of to find the leak (if the seal is the problem)

2) Not a seal leak then the other issue must be the Check Valve... it should be a 1 way valve but it could be out of life and wont hold air going one way anymore, or just a bad check valve in the first place...


these would be the 2 main things that would stop a siphon from a pvc overflow...
I don't see any leaks from a bad seal, but I have tried using a two part epoxy to make sure the fitting in the pipe is sealed. I don't see anything or hear anything coming from there.
As for the check valve, I have tried using a new check valve and even began the siphon by mouth then pinched the hose and plugged it to make sure no air leaked and still nothing.
 

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Here is an image of my design working well for a few weeks now. I don't use the airlifter and once primed the siphon is maintained.



Increase D to be able to handle larger flows as the level differential will force more water through any given dia pipe. With a D of 1.5" on a 0.5" PVC I get 1 GPM.

Keep S to at least 6" to 12" to maintain the siphon.

Length I needs to be only 2-3" more than D to allow the intake to handle large surges of flow.

I would also suggest building a unit with two siphon tubes connected externally with a T into a common drain. This way if one siphon stops the other maintains flow.

Getting to your original question - and looking at the video,I think the outside U loop on your siphon is too small and can allow air to travel from the outside vent back into the siphon during periods of low flow. A second possibility is that the surface skimming tube pulls air pockets which accumulate in the top of the siphon tube. You can probably see a vortex hovering over the drain during periods of high flow - that's air going in the line. Eventually enough air can get trapped and break the siphon.

A better solution is an overflow box in the tank with an inverted U tube arrangement. In my setup I simple added filter screens to the ends of my U siphon tubes-too cheap to buy an overflow yet!!

I hope this makes sense.
 

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Discussion Starter · #5 ·
I would love to use an overflow box, as I use one on my display tank. However my main tank houses fish and is full. The tank that's having a problem is a turtle tank and is not full
 

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This is the one I personally prefer.
 

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Yeah - that looks great. The over flow diameter or cross ection should be 2-4X the diameter of the siphon tube so that the 'waterfall' is relatively gentle. Otherwise the downward flow of water in the waterfall is fast and pulls air pockets into the siphon.
 
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