The Better Bell Siphon

I’ve been using bell siphons for a few years in various grow beds. When I went to larger beds, I ran into problems getting the siphon to stop properly. Here is an overview of how I’m setting up the siphons in the new greenhouse, where the problems were, and how I resolved it. This design uses a trap to help start the siphon. When the water level rises, the bell area becomes sealed by blocking the breather tube. As the water level continues to rises, the trap blocks the air from escaping and the pressure inside the bell is slightly greater than the atmosphere. The pressure keeps pushing against the water in the trap until it pushes enough water out which “burbs” a few bubbles out. This reduces the internal pressure and the water level inside the bell will quickly rise a bit. This process continues until the water level reaches the standpipe height. The next “burp” will send a rush of water down the standpipe and the siphon action will start. The air inside the bell is evacuated and the siphon will also draw water through the breather tube. The water level will then start to go down until it gets to the opening of the breather tube. When this happens a large amount of air enters the bell and stops the siphon. The problem with large grow beds is that the water level goes down very slowly, so when the air enters the breather tube, it doesn’t suck quite enough air and the water in the siphon slows down and makes it get stuck in limbo and it will continue to trickle water out at the same rate that the bed is filling. To solve this problem, I simply placed a little cup under the breather tube. As the water level rises the cup gets filled with water and sinks which seals the bell. The bell siphon will operate normally and start up when the grow bed is full. As it drains, the water level will get to the height of the cup. At this point, the breather tube still has water being drawn through it and starts to suck the water out of the cup. This makes the cup buoyant, forcing it to rise. Once all the water is removed from the cup, the breather tube sucks only air, which does a clean break of the siphon. Since the cub is buoyant, it isn’t able to flood with water until the water level in the bed starts to rise again. This is a close-up of the cup floating until the water level forces it to sink. This shows the water level in the breather tube and displays how the pressure inside the bell keeps the water level lower than the outside water. With this setup, the top of the standpipe is about 2” lower than the external maximum water level. Typically the entire bell can be underwater before it starts to siphon. Here is the water level getting low enough so the water can no longer fill the cup. The breather tube sucks the water out making it float, then it is forced to suck only air, breaking the siphon. Thanks for watching. Please leave a comment below if you if you tried the floating cup solution or if you found this video to be helpful. I’ve added some raw video at the end that shows all the parts I used for my bell siphon assembly.

Channel: Bigelow Brook Farm (Web4Deb)

Views: 484,218

Rating: 4.9361296 out of 5

Keywords: aquaponics, hydroponics, bell, siphon, syphon, loop, grow, bed, geodesic, dome, greenhouse, autosiphon, yt:stretch=16:9, growbed

Id: 4hHRe3KJfoY

Length: 4min 51sec (291 seconds)

Published: Mon May 14 2012

Reddit Comments

[u/darkwing_duck_87]

I just spent a bunch of hours yesterday and a few more today trying to get my bell siphon to work properly (doesn't have the "better" pipe off the side). I keep getting stuck in limbo, as the video says. I'm pretty sure I'll have to go to this system as I'm using an IBC, which I guess is a larger system.

I'll be back out there Monday and I'll see if I can't rig one of these up.

[u/col381]

I really think he is over thinking this whole thing. I have three bell siphons in my system and they have worked reliably for well over a year now, nothing like the problems seen here, and I have nothing like the fancy air pipes or floating cups seen here.

Stand Pipe & Tank Fitting: I use a simplified version of the Affnan design, so have a reducer fitting at the top of the stand pipe (seen here in an earlier design). This serves to form a 'cup' at the top of the stand pipe which lets in more water at the beginning of the cycle, which allows it to start easier.

The stand pipe sits in a standard tank fitting that goes through the bottom of the grow bed. This just a commercial fitting with a double adapter F-F screw on the top. A key feature I added was that I drilled a hole through two pipe caps, one 50mm(for the bell) & one 100mm(for the shroud) that serve as holders for the bell and outer shroud. I cut some slits in the sides of the inner cap end (the bell siphon one) to allow me to remove the bell easier and to free up space for the air holes on either side.

Bell: The bell itself is just a basic bell with holes at the bottom, this is far simpler and much more reliable that the 'air pipe' design being used here. In this pic you can see the bell in it's holder as described above.

I take care to make sure that the gap between top of the Affnan cup and the top of the bell cover is no more than around 1cm, this seems to work best.

Shroud: I cut slits in a 100mm pipe using my mitre saw, this is much better than drilling holes. The slits are less prone to blockage and you don't let small rocks in so easily. Also much easier to do. The shroud fits into the second of the end caps I have as part of my tank fitting and that stops it moving around. The top of the shroud is just a drain cover I use that can be removed easily. Here is another pic showing the top view with the top off once everything is together. (This pic really shows how much more compact not using an external air pipe makes things)

Exit: At the bottom of the siphon is use a simple straight pipe with a further reducer on it (seen here on my 'test' bucket') instead of mucking around with elbow joints and upwards section etc. The reducer, coupled with the affnan reducer cup at the top of the pipe help the pipe to 'bunch up' the water once it starts to flow to allow for easier starting.

Tuning: The final (key) factor in getting this bell design working reliably is making sure to properly tune the water flow. When I initially started using the design I had troubles getting it either to start or to stop at the end - both classic problems with bell siphons, but one I had sorted out the design issues to settle on the above design, I found the #1 factor in getting it work reliably had nothing to do with the bell itself. You have to make sure you tune the water flow to be just right. If the water is running too fast the bell will start but not stop. If you are running the water too slow it will not have enough water flow to start properly. By adjusting the flow rate just right you hit the sweet spot where it both starts easily and stops easily. After a small amount of practice it's really easy now, takes me mere seconds to set the tap just right these days and the siphons work perfectly for month on end.

That's it, this design is much more compact, has zero moving parts, doesn't rely on silicone to seal against air leaks and doesn't have stupid poking out bits and floaty bits all over the place.