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I've been experimenting with the bell syphon recently and came across the following situation. The syphon worked great during my experiments when test filling the bed with the garden hose, but when I switched over to my pump the syphon did not engage. I went back and used the hose method again and it worked. The hose brought water in to the grow bed at a higher rate which led me to the conclusion that the flow rate of the incoming water has to be significant enough to force the water high enough over the stand pipe to create the vacuum otherwise the water just trickles over the stand pipe and never actually drains. So the question is, is there a "magic" formula for determining the incoming flow rate and/or does the size of the stand pipe relative to the bell syphon also influence the vacuum's ability to engage or not? I'm also curious as to whether the amount of head room between the top of the bell and the top of the stand pipe would make any difference.

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Comment by JD Sawyer on July 7, 2010 at 9:13am
Good tip on the Affnan bell syphon. That's definitely the best explanation I have read to date and the schematics are very helpful. I guess it helps to have 30 years of aerospace engineering under your belt, too... Here's the link below for other's who are interested in this design.
http://affnan-aquaponics.blogspot.com/p/affnans-vave-detailed-explanations-of.html
Comment by TCLynx on July 7, 2010 at 8:00am
Yes flow rate is significant to siphon operation. Yes there are formulas to figure it out. Some one over on the BYAP forum did this years ago. Sorry I don't have the link on hand to post, I would have to search for it.

However, you might be better off looking up the Affnan siphon design as it might solve your troubles.

If unwilling to change to the Affnan then adding a trap at the bottom of the siphon can slow the trickle over to help starting up under low flow conditions but then you will probably also have to add a breather tube to help the siphon stop as well.
Comment by JD Sawyer on July 6, 2010 at 5:17pm
Cool thanks Rich. Hey, there about 20 perch still alive and kicking in the GH system btw... When's the last time you've been over there?
Comment by Richard Wyman on July 6, 2010 at 5:03pm
The head height should be about 3/4 to one inch, and the drain pipe below the bed should have a couple bends (I like to use 3 45's) in it to slow the water down, that seems to help the most.
As to a magic formula, I have never seen one.

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