# Siphon



## dogman (Aug 2, 2006)

I have looked around on the net and found a few designs of DIY continuous siphons, none of which I like the looks of. I have an idea of how one might be made and was hoping to receive some feedback from someone that might know a little more about fluid dynamics than I do. The design is very simple and I believe that the diagram is self explanatory. I am thinking it could be made of any size tubing and in my case 1/2” pvc will give plenty of flow. What do you think, will this work or am I missing something. 
Note: Good only for very slow flow ie. continuous water change, in my situation.


----------



## hoppycalif (Apr 7, 2005)

I'm not sure what the goal is for this. Is it intended to maintain the level of the water in the tank?


----------



## dogman (Aug 2, 2006)

Yes, that is right the goal is to maintain the desired level of water in the tank. I have a very limited amount of space to work with behind the aquarium and I am just looking for the least obtrusive way to create a continuous siphon.


----------



## schaadrak (Aug 18, 2006)

If you're going to be adding new water to the tank and want the water carried away at the same rate, an over flow is going to be your best bet. Trying to balance the input of water with the out-take of the siphon is going to take a lot of work and if just one thing goes wrong, the tank can be in serious trouble from being too low (which will break the siphon eventually) or over flowing.

You just need to add an overflow box around the intake and ouput of your siphon and have the drain come throught the bottom of the output box at a point thats higher than the siphon ends.

Like this:










When the water in the tank rises and falls into the overflow (1) it raises the level inside the box (2), which forces water up into the siphon (3) and into the box outside of the tank. When that level raises enough, it flows into the drain (4).

If the flow is low enough, you could probably get away with just using larger diamter pipes for the "boxes" if you're that pressed for space.

I hope I explained that well enough to make sense.


----------



## BryceM (Nov 6, 2005)

If drilling the tank is an option, a bulkhead is an elegant solution. Nice & simple.


----------



## Charlutz (Oct 17, 2006)

Hi, I am new to the forum. First post in fact. I am a fish guy looking to add plants to my tanks. But I have experience with overflows and sumps so thought I'd chime in. If the goal is to maintain a specific tank level under minimal pump inflow, like a continuous fill setup, then drilling the tank is your best bet because it does not rely on a siphon. Overflow boxes with siphon designs are great (my setup uses one) but the one 'flaw' they have is that under low flow rates, like less than 300 gph, small bubbles will accumulate inside the siphon tube. The flow rate is not strong enough to push them through and when enough accumulate, the siphon will break and the overflow will stop draining. There are measures against this - like monitoring the siphon and sucking out the bubbles, increasing the pump flow to 'blow' them through, or using smaller sized siphon tubes to get a higher flow rate, but there are potentials for a breakdown. If you are using an overflow in a continuous topoff system, drilling the tank is a much better solution as gravity is immune to bubbles.  The siphon overflow boxes work much better when used with a sump system where the flow rate is practically unlimited since it is a closed system.


----------



## bpimm (Jun 12, 2006)

dogman said:


> I have looked around on the net and found a few designs of DIY continuous siphons, none of which I like the looks of. I have an idea of how one might be made and was hoping to receive some feedback from someone that might know a little more about fluid dynamics than I do. The design is very simple and I believe that the diagram is self explanatory. I am thinking it could be made of any size tubing and in my case 1/2" pvc will give plenty of flow. What do you think, will this work or am I missing something.
> Note: Good only for very slow flow ie. continuous water change, in my situation.


Yes your drawing will work I have done similar things in the past. The issue with the bubbles building up in the siphon is real, to overcome this in your application you can drill a small hole in the top of the siphon loop and glue in a short piece of hard airline tubing for a nipple then route soft airline tubing from the siphon to the air inlet of a power head in the tank. this constantly pulls a small amount of water out of the top of the siphon loop to keep the air out. also on the outlet of your drawing use a tee vertically with the top open so the drain line can never pull a vacuum on the siphon or it will drain the tank down and break the siphon.

As stated before drilling the tank is the best, but siphons do work and if you already have a power head in the tank then it's simple to add the line to the siphon. if it is a strong power head it will actually start the siphon for you by sucking the air out and pulling the water up.

Good luck with the continuous WC, I've been using it for over 10 Years and will never go back.


----------



## dogman (Aug 2, 2006)

Thanks for all of the great feedback. I had not given any thought to the air bubble problem and in pointing it out you have surely saved me a wet floor. Thanks again.


----------

