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Hello all. If there is anyone that can help me please I would greatly appreciate it. My bell siphon will initiate a steady, good flow within 30 seconds, but stops leaving about 5 inches of water in the grow bed each time. I am stumped as to why that is. My stand pipe is 3/4", my bell siphon is 2" wide lined with 1/2" holes along the bottom. The downspout has a right angle about 6" vertical, 7" inches horizontal and an elbow at the end to control the back pressure. I've tried playing around with that, but it doesn't change anything. I would be more than grateful if anybody has suggestions. Thank you!!

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Hi NG

Like Jim said, there's a lot of info on the web; www.affnanaauaponics.com, www.japan-aqauponics, and from the College of Tropical Agriculture and Human Resources, University of Hawaii at Manoa; The construction of Automatic Bell Syphons for Backyard Aquaponic Systems. I thought these were great sources of info for me. They go into a lot of detail with plenty of pictures. When I put mine together, I put it together dry and then put a bead of silicone around the seams ie bell and my syphon hose and then I let them dry overnight. When I realized that they would work, I built 2 more so if these 2 were to develop issues, I could just swap them out . 

Yes this make perfect sense now that the facts are out. Your siphon has to fight gravity too much because the volume of bell is slightly too large. At some point mid way the weight of the water in the stand pipe is less than that in the bell above the water outside the bell and the siphon stops. It simply can't lift up the water inside the bell.

Also the fitting I mentioned it is a common pvc fitting. I use  that on all my grow beds and it has solved problems related to when the siphon stops, particularly with a siphon that does not stop which will be the next problem you encounter... also the fact that you have two elbows in the drainage flow might be causing reduced flow and a weaker siphon. Going from 3/4 to 1 1/2 will make sure the pipes below the grow bed  aren't restricting the flow of your siphon. You should not need a breathing tube with this fitting.

N.G. said:

Huh. a reducing 3/4 inch to 1 1/2 inch elbow? Never heard of that. Is that a common piece I could find at the hardware store? I just picked up a stronger pump, to see if that might be my problem. maybe that will help? I will definately search for that piece. Thank you so very much!

Jonathan Kadish NYC AA Chair said:

Well this might or might not fix this problem but you want a reducing elbow at the bottom of the standpipe going from 3/4 inch to 1 1/2 inch and having the pipe leading back to the fish tank be 1 1/2 inch pvc. This allows free flow from the stand pipe and allows air to enter from the bottom to break the siphon when the flow slows when the bed is nearly empty.... I hope that is the issue :)

Jonathan, do you mean an elbow that is 3/4" on one side and 1 1/2 inch on the other? Then use 1 1/2" pvc for my horizontal leading to the fish tank? I just want to be sure I'm understanding that right. Thanks! I'll do some searching at the hardware store.

Yikes, lots of advice here. Not sure where to start so I will start at the beginning. My siphons are based upon Affnan's work and I have made and sold over 500 siphons to folks all over the world now and in all sorts of sizes and none have ever failed to work.

So having qualified my answers here is the formula. 2-1. That is the basis of a good siphon and it is almost just that simple. In other words a 3/4" stand pipe requires a 1 1/2" funnel on top but using a 2" bell you will have to settle for a 1 1/4" adapter so it will fit into the bell but that is in range. Everything else you did is right on ASSUMING you have no leaks in your bell cap. Any air leak there WILL screw up your vacuum in the bell. That could be your problem. I can't tell from here but a real cover (not sure what you used) properly glued simply will not leak ever. Photo below.


It matters little how much room you leave above the funnel (within reason) but it should certainly be no less than 1/4" in a small siphon BUT I leave about 2" or more room so that I can add extensions for very important reasons that folks tend to never think about. For example: If you are planting seeds directly into the GB, 2" of dry media isn't going to cut it so I drop a 1 1/2 inch section of pipe (+ 1" for into the funnel of course so really 2 1/2") so the water level can be instantly adjusted to 1/2" from the surface. For seedlings I drop that to 1"and when I find evidence of cut worms or slugs, etc. I drop in a 3" extension and flood the bed and wait for the critters to come up for air for easy pickings. With my 1" standpipe I use a 1" to 1 1/2' adapter and then place a 1 1/2" to 2" adapter on top of that for a perfect funnel shape. So I use 2" pipe for the extensions and even include one size with each siphon or I sell a full set of 4 in 1/2" increments. With the 1 1/4" funnel top you need to use couplings cut to size as you are using a male adapter whereas the 2" funnel is a female but the idea is the same.

For those who want to understand why, question: which will pass more water over the top of a vertical 1" pipe? the pipe itself or a 5" funnel? Pretty obvious. If you want a say 1" pipe to fill with water FAST and thereby start a siphon fast you send it all the water you can and that is done by dropping a funnel on top. Not rocket science.In our case there is a sweet spot and Affnan nailed that to be as close to 2-1 as possible given pipe sizes and wall thickness.

Now for the other end of the siphon formula "breaking siphon". You DO NOT WANT A TRAP below the GB. One or two 90's will create enough resistance to flow to allow the stand pipe to fill completely and help the funnel above. They work together. But what is most often overlooked is: when it is time to "break siphon" you need to get lots of air back into the standpipe and drain pipes FAST as well. This requires air to come under the bell AND back up the drain pipe from below the GB. A trap will interfere with that of course and then you get into "snorkel tubes" to try and fix a bad drain. You do not need noisy leaky snorkel tubes. They are totally unnecessary if you avoid traps and that means making sure you are VENTED right after the last 90 (whether you use one or two) and making sure the drain part of the siphon does not run up hill as that will form a trap as well. My first 2 GBs would hang occasionally while the next 3 would always work perfectly. I finally realized my first 2 drains were running up hill just enough to form a trap under there. Once I crawled under there and replumbed them level they never hung again.

Here is a very old picture of my first ever Barrelponics siphon which is equivalent to yours: Note the funnel and the well sealed cap. You will need a handle if you want to keep the gravel guard (3" in this case) as small as possible and you do! Don't waist valuable grow space with a giant gravel guard. I never understood that mind set not to mention cost. Be sure and replace the drawer pull screw with a 3/8" ss screw. I make my slots in the gravel guard about half way up the guard as that is all you need.

Siphons really are that simple and they get more advice on here, YTube, etc. than any other AP subject. KISS.

Also remember that when your media is in place you will only be handling about 1/2 the water volume but it should still work flawlessly either way. Hope I covered everything. Let us know how you make out.

Yes, usually I go from 1/2 to 3/4 inch. It may be fine to go from 3/4 to 1 inch. You can try different configurations just as long as you are making it  so the water doesn't completely fill the pipe below the grow bed

N.G. said:

Jonathan, do you mean an elbow that is 3/4" on one side and 1 1/2 inch on the other? Then use 1 1/2" pvc for my horizontal leading to the fish tank? I just want to be sure I'm understanding that right. Thanks! I'll do some searching at the hardware store.

N.G. Your elbows are fine. Just test that bell cap for leaks or replace it with a real cap and not the cheap "test" caps. The only other change might be the 3/4" to 1 1/4" funnel top. I can't tell how big yours is. But if your siphon is starting fast then I say you have an air leak in that bell.

Jonathan Kadish NYC AA Chair said:

Yes, usually I go from 1/2 to 3/4 inch. It may be fine to go from 3/4 to 1 inch. You can try different configurations just as long as you are making it  so the water doesn't completely fill the pipe below the grow bed

N.G. said:

Jonathan, do you mean an elbow that is 3/4" on one side and 1 1/2 inch on the other? Then use 1 1/2" pvc for my horizontal leading to the fish tank? I just want to be sure I'm understanding that right. Thanks! I'll do some searching at the hardware store.

Jim and Jim, I switched out the caps and that definately solved my problem of not siphoning completely because it did drain all the way down as it should and I started rejoicing a little early. The only problem now, is it doesn't gurgle like it should when it gets to the end and the siphon never stops. I also tried the 3/4" to 1 1/2" inch elbow reducer on the down spout but that did not help it drain. It was definately the cap!! I just want to say how grateful I am for everyone's suggestions. As I respect Affnan's design and principles physics was never my favorite and some of the diagrams and long explanations seem to go right over. You guys have been so very helpful and I really appreciate all the time, expertise and explanations. I have to ask one other thing. I will do some research but does anyone have any suggestions of how to stop my siphon???

I have a 1" funnel on the top. It would be nice if it started faster than it is. I will give that a try if I can find one. Thank you!!!!



Jim Fisk said:

N.G. Your elbows are fine. Just test that bell cap for leaks or replace it with a real cap and not the cheap "test" caps. The only other change might be the 3/4" to 1 1/4" funnel top. I can't tell how big yours is. But if your siphon is starting fast then I say you have an air leak in that bell.


That is my only crit of Affnan's site. The weeds. My eyes glazed over as well when I first started following his advice. Hard to get past the weeds. Genius nonetheless. I am not sure even he understands the importance of the air coming back up the downtube at "break" time. Try shortening your pipes below AND try one 90 rather than 2. If that works but you still need to direct it down or to the side then add a T before the second 90 with the side port aimed up for more air getting back in there between 90s. Run an air vent up from the T. Venting at the right spot is perhaps the most overlooked piece of the puzzle. ALSO you may need to run a pump bypass so you can regulate the flow without loading or restricting the pump. Your last problem there could just be too much flow.

N.G. said:

Jim and Jim, I switched out the caps and that definately solved my problem of not siphoning completely because it did drain all the way down as it should and I started rejoicing a little early. The only problem now, is it doesn't gurgle like it should when it gets to the end and the siphon never stops. I also tried the 3/4" to 1 1/2" inch elbow reducer on the down spout but that did not help it drain. It was definately the cap!! I just want to say how grateful I am for everyone's suggestions. As I respect Affnan's design and principles physics was never my favorite and some of the diagrams and long explanations seem to go right over. You guys have been so very helpful and I really appreciate all the time, expertise and explanations. I have to ask one other thing. I will do some research but does anyone have any suggestions of how to stop my siphon???

Lowes # for the adapter is 23914 and costs .96.

N.G. said:

I have a 1" funnel on the top. It would be nice if it started faster than it is. I will give that a try if I can find one. Thank you!!!!



Jim Fisk said:

N.G. Your elbows are fine. Just test that bell cap for leaks or replace it with a real cap and not the cheap "test" caps. The only other change might be the 3/4" to 1 1/4" funnel top. I can't tell how big yours is. But if your siphon is starting fast then I say you have an air leak in that bell.


Ahhhhhh! This is fantastic! Bell siphon music to my ears!  Thank you Jim!!!! You are a genius. I picked up those pieces, the T piece for the downspout and the 3/4" to 1 1/4" funnel (It was the exact part number you said) and at first it started really nice but didn't stop, BUT that was when I had the pump turned all the way up. When I decreased the flow in the pump it drained and gurgled and filled again just like it should!!! I love it! I think now I just need to find the sweet spot flow?  My wee one has been anxiously awaiting fish as I promised her so she is supper thankful and I don't have anyone at home to bounce ideas with. Thank you so much. Thank you to everyone :) Can I add you to my friend list on here?

Hell yes! I just sent a request to you. I never tire of helping people get-er-done. I just posted a blog on our SLO so ck it out. It might be of some help as well. This is by far the best forum around with the best folks that love to help.

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