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Comment by Homefire on March 14, 2011 at 10:13pm

Thanks Burton and David for your suggestions.  I've just started cycling up since winter pause. 

I turns out that the lower end of the drain needed more fall per run.  The drain pipe needed to empty completely to stop the siphon.  Before, with even a little moving water in a full drain pipe the siphon would pick up again after the breather tube had broken it.  

Comment by Burton on March 14, 2011 at 6:24am

Ok several questions.

• Did you remember the notches at the bottom of the bell? (example http://120thingsin20years.blogspot.com/2010/04/aquaponics-bell-siph...)
• Is the "air tube," pictured touching the wood, above the bell and given enough clearance to do its job (example http://affnan-aquaponics.blogspot.com/2009/06/aquaponics-siphon-explained.html)

Some points to consider, the glass water bottle is a poor choice to "see" what is happening because it is tapered and will actually create a Affnan type syphon effect because there is less surface area of water to move given the volume of pipe / water.

 

Try finding a plastic water bottle and cutting it in half and use the TOP part of it, less chance of a parallax this way too. Make sure not to block the air tube when doing this, there is a good demonstration of this on youtube.

 

You could also consider removing the current bell and replacing it with a larger one, but you will need to use a reducer like in the Affnan's bell siphon to reduce the amount of water area needed to start the siphon.

 

Comment by David Waite on March 13, 2011 at 10:10pm

Homefire is the water leaking down the drain pipe through another hole. Cant see why your siphon is starting before the water ever gets over the drain. Siphons dont work that way unless your pipe is allowing water to enter at a lower port or the end of your drain is under water. I have built alot of siphons and havent run into what you are up against. It has me puzzled. You can see my siphon if it helps.

Comment by Homefire on November 9, 2010 at 5:06pm

That volume is doing something. When i used the shorter plastic cap, i have had the level in tub higher. But after the siphon vacuum break pressure should be equal, one atmosphere, both inside and outside of the drain.

If i remember hydraulics though, a large column of liquid will push a smaller column higher. Thinking of an hydraulic jack where a small column, forced by a piston, lifts a larger column a shorter distance but with greater force. The tub situation is reversed. The large column, rising water in the tub, pushes a small column, in the drain, farther and faster than the large column. So the drain starts before the level reaches the top of the tub.
I tried raising the drain tube. That gained me an inch or two. Since the small column is rising farther faster than the tub i can't make the drain tube high enough.

Comment by Dan Brown on November 9, 2010 at 3:40pm

Wouldn't the air pressure in the added volume of that shape contribute to the forces initiating siphoning?

Comment by Homefire on November 9, 2010 at 2:41pm

Thanks Daniel.

I'm still mystified as to why flow starts when water level is still 3-1/2" below the drain tube. I guess there's enough vacuum despite the clear vacuum break to pull a column that high. I would like the water to rise within 1" of the tub rim.

Homefire

Comment by Dan Brown on November 9, 2010 at 12:09pm

Genius idea for showing the process.