building a small bell siphon

[Anne Phillip]

Has anyone built a system with a small diameter bell siphon?  I'm thinking of one with 1/2" or 3/4" stand pipe.

What's your experience with smaller siphons, what issues or adjustments did you make to be successful?

[John Cubit]

I currently have a small indoor system using a 3/4" x 9" stand pipe with a 1" flair on the opening.  The bell is a 2" diameter. It does work but.... It is sensitive to the exact water flow, it would either not kick off or not shut off.  I have had to test about a dozen shutoff valves before I found one that actually did a fine adjustment to the flow and I have to redo the flow about every 3 months or clean the pipes thoroughly. Solids and algae do form a buildup.

I have gotten quite used to it over the past 2 years but if I had to do it again I would have gone to a 1" stand off that is in my outside system and works fine.

[Jeff S]

I have a 1 inch, 3/4" and recently 1/2" siphons. I seem to have the same problem with all of them that you are having. I've seen the ones with the external tubes that seem to take care of the shut off problem. With that you can probably turn up your flow to take care of the starts. Check it out... https://www.youtube.com/watch?v=CXaruS5z_Xc

[Jim Fisk]

Guys, I make them for part of my living and if you follow some simple rules you will have no problems with them at all. You do not need any snorkel tubes or traps but you must follow some simple rules. The top of the stand pipe must be twice the diameter as the pipe. I use adapters. (2 for the IBC size) You then need a couple of 90's below. That is it. That 2-1 ratio at the top ensures a fast "make" (the siphon starts) because it lets twice the amount of water fill the pipe at once compared to a straight tube. Just in case you have a very small flow the 90s below the bed slow the water down just enough to also help fill the tube, kind of a secondary back up to the funnel top.

A fellow by the name of Affnan did all the math and testing but not everyone wants to wade thru all the weeds so I am giving it to you straight. Doesn't mater what size or height (within reason) you make. ALSO you must have some kind of air gap, could be a T and pipe vent, etc. after the second 90 or the siphon will not "break" (stop flowing) as the air that breaks the siphon needs to come from BOTH directions, from below and above. If just dropping to a FT below nothing else is needed but if feeding into a common drain line it must be vented just like every sink, shower, toilet, etc. in your house. That will ensure it does not "hang".  If you follow what I have laid out here it will work. Period.

I have sold over 300 siphons in the past year and they all work. I make them in 1" x 12" for IBCs, 3/4" x 10" for barrelponics and 3/4" x 5" for shallow trays. I will be happy to help anyone make their own although it is so simple I don't think you need much help if you have the tools and some common sense and follow these rules. The IBC size uses a 3" dia. bell and a 4" dia. gravel guard. For the smaller 3/4" ones I use a 2" dia. bell and a 3" dia. GG. I use a male plumbing threaded adapter and a female ELECTRICAL adapter (no tapered thread so you can tighten it all the way down) and one "O" ring that goes below the GB bottom in either size. I get everything from Lowes. That's it in a nutshell. You can see pictures of them on my photo page by clicking on my avatar. Any questions feel free to ask but I like to answer here where all can follow along rather than personal messaging. If you have one that is acting up just post a picture and I can help you correct it.

[J4n90]

I used this one in my system, seems to work nicely.
http://m.instructables.com/id/Make-a-Bell-Siphon/

[TCLynx]

Like Jim says, the Affnan modification (basically a 2-1 funnel at the top) tends to make siphon flow balancing much easier.

To note however, you must be able to adjust the flow into your bed so you can make sure your siphon will balance AND there must be a little fall below your bed for the siphon to drain (you can't have the bottom of your bed basically at the exact level of the water tank below it or the siphon will never be able to break/stop.)

Barrels cut the long way on their sides will always be a little trickier to get the siphons to balance since they have a varying volume by depth so the barrel essentially seems to fill slower at the top while it seems to fill faster at the bottom so definitely give yourself a break and use the Affnan modification and don't cut corners on being able to adjust flow and give yourself some height to work with under the bed when messing with siphons and barrels cut the long way.

That said, I've made little bus tub systems where I use a 1/2" stand pipe and a 1"down to 1/2" funnel type adapter/coupler with a 2" bell over it and some plastic mesh as gravel guard and it works quite well.

However, keep in mind that if you plumb in for 1" fittings, you can always adjust down using bushings  but if you set up the system with too small of plumbing, it is trickier to make the holes bigger.

[Suzanne Hayes]

I have a 3/4" bell using soda bottle tops for the funnel and then another larger soda bottle for the bell.  I haven't had any problems on my larger 50G bed, but my smaller bed wasn't shutting off, but that turned out to be because the drain was running slightly up hill, once I rotated it down, no problems

[Robert Rowe]

If you make  the Bell Syphon and the media bed proportionally smaller, there is no reason for it not to work. 

[Jim Fisk]

Yes, Suzanne nailed a common problem. Basically having an unintended trap below the bulkhead fitting that does not let air come BACK UP the tubes at break time. I had that happen on my 2 oldest GBs and having glued it all I waited awhile to correct it and sure enough that was all it took after playing around with everything else that was easy to do like snorkel tubes, etc. and those offered no real relief. So take your time and get the plumbing LEVEL. Also the top of the funnel should be level so the water cascades over the top all around at once or it defeats the whole purpose of the funnel.
Also on the small funnel (3/4" stand pipe) it occurred to me that I break the rules a bit and use a 1 1/4" adapter rather than a true 2-1 (1 1/2") so it fits into the 2" bell easily. Has never been a problem. If the 2" were just available in S&D thin wall the 1 1/2" adapter would fit but alas it is not.
Suzanne Hayes said:

I have a 3/4" bell using soda bottle tops for the funnel and then another larger soda bottle for the bell.  I haven't had any problems on my larger 50G bed, but my smaller bed wasn't shutting off, but that turned out to be because the drain was running slightly up hill, once I rotated it down, no problems

[Anne Phillip]

Thank you everyone for your excellent replies! I really appreciate your input and knowledge. I love being a part of this community!

[Jeff S]

Gonna go back now and rethink my siphons.

[Jim Fisk]

Since a picture is worth a thousand words, here is the 3/4 inch small siphon we make and you can copy:The blue knob allows you to pick up the bell in a 3" gravel guard. (replace the steel screw with a ss screw) Your GG should be as small as possible to allow more grow space which is after all why we are doing AP. The pipe lengths aren't written in stone. Just make the standpipe fit your media depth. Also make sure there are no air leaks in the bell. Use silicone at the knob screw and pvc cement to attach the cap to the bell pipe.

[Anne Phillip]

That looks great, Jim!