Backyard Aquaponics
A place to discuss aquaponics

This is an explanation of how a traditional bell siphon operates. It goes into some of the physics of how the auto siphon gets started and stops. One of the biggest problems I've run into is getting them to stop properly on large grow beds. I've solved this problem with one simple little piece! It's so simple, I'm kicking myself for not figuring it out years ago!

This grow bed is using 3/4" pipe for the drain and standpipe with a 2" bell. The fill rate is LESS than 1/2 liter per minute and the siphon still starts with no problem. It's been running for about a week without any problems.

You say the traditional bell siphon works best for small grow beds but found the trapped air is a problem for the larger grow beds. Are there approximate sizes for these or does it just depend on the set up?

I would say that anything that's a tote size or smaller would be more of a traditional size. Most people just play around with their siphons until they can get it to work with their system. With this one, it doesn't seem to matter what size bed you're using. The flow rate doesn't seem to matter much either. Surprisingly, I had a really hard time getting this siphon to fail!

Nice solution.

Could you not also achieve the same result by pointing the opening of the breather tube up?

You really need the float part of it so that it can rise up above the water level. If you just looped the tube up, it will probably suck water in with the air.

Do you really need the "U" bit at the bottom of the drain?

Technically, for a true bell siphon, the answer is yes. If you want to have a slow fill rate, you need the back-pressure and burping effect to get the quick surge of water to go down the tube to get the siphon started. Most siphons that are out there, rely on either enough inbound water flow to create a little choke point somewhere inside the standpipe (or elsewhere in the drain) which is enough to give the siphon a kick.

Also, I'm not saying that these other methods are wrong...I'm just saying that if you want to have a fairly slow flood rate, you need the trap so that it can help get things going.

Ingenious, well done. I was going to post a new thread on inventions this morning any way but this makes it even more pertinent.

This device (improvement) makes any bell siphon or affnan's siphons cut out instantaneously each and every single time. You no longer will have any cut out problem using this small addition.
It will operate on any fast or very slow filling system.

Some people may have missed this posting.
What this means is that this can be used on any bell siphon or affnan's siphons.
They will not effect the starting of any of those siphons in the way they operate.

Only issue I see is the current setup people have need an alteration - the media guard needs to increase in size or be set off to one side to allow room for the cup.

Although I suppose the cup doesn't actually need to be the size shown in the video, if just needs to be big enough for the air tube and a little slack.

Nice idea.

I think you have found the solution to every 'syphon break' issue ever recorded Rob. You da man!

What a bloody Beauty! Rob, again you have shown the Benchmark.
Brilliant!

cannot see siphon

Ok, I have just been out at my AP to trial Rob's design and I will say.... IT WORKS LIKE A DREAM!!!!!!


Well done Rob, fantastic design and idea. My design is a little different to yours only because my syphon design is different but the process and outcome is the same. I will admit that I dont have the 'U' bend at the bottom of my standpipe but it works just fine without it.

As Afnan has done in the past...... I think we shall name this 'Rob's syphon break'..... what ya recon????

I'll Second that Charlie, because I too have been on the Greenhouse mucking about with the floating cap and this system works with my U-Siphons too.
Rock on!


The U at the bottom of the drain makes no difference to the success of this, i have no U in my drain and it still works.