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It is essential that the drain line from the tank pass through the 2"x1" bushing and connect to the 1" 90 deg elbow. Glue the contact spot where the 1" drain pipe passes through the 2"x1" bushing as well as all other pipe/fitting connections.

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Comment by chuck on October 16, 2011 at 6:36pm
Comment by Jon Chaiton on September 12, 2011 at 2:29pm


A couple other details:  I normally put a perforated bowl upside down over the bulkhead fitting so that media does not clog the opening.  Then I bury the inverted bowl with media.  Also I insert the 3/8th inch airline inside a piece of perferated tubing with a perferated cap at the bottom of it so that the airline does not get clogged either.  I usually use 1/2" PVC which extends upward and out of the top of the media.  The airline simply slips into this tube until it reaches the bottom, then is pulled back about 1.5 inches and secured with a plastic wire tie (zip tie) to make sure that it is always at the right height.

Comment by Jon Chaiton on September 12, 2011 at 2:15pm


Hi. I have built dozens and dozens of these things and they work perfectly.  You are correct about the fact that you do not have to worry about the media getting into the bell siphon or the notches (or "v" cuts) at the bottom of the bell getting clogged, because there are no notches with an outside bell siphon.  The bell siphon (2" PVC outer pipe) has a 2" PVC male adapter glued onto the bottom of it.  This male adapter threads into the top portion of the 2" PVC Tee, so that removal, service and cleaning is simple.  I normally add a 1" PVC ball valve to the drain line between the tank and the bell siphon and another one after the bell siphon to control drainage if necessary.  By closing off the ball valve between the tank and the bell siphon, momentarily, it is easy to service the bell siphon if necessary.

In answer to your initial questions, the 1" PVC drain line acts as an outside standpipe to control water level.  As the water fills to the top of the bell a siphon is formed and gravity pulls the water through the bell and out the bottom of the bell through the 2" tee to the lowest drain line (the water has no where else to go).  When the water level in the tank gets near the bottom, air enters the 3/8th inch airline and breaks the siphon and the whole thing begins again.  One thing to remember is that the flow rate into the tank must slightly exceed the capacity of the outside standpipe to handle that volume.  Otherwise the water will just flow down the standpipe and no siphon will occur. That is why it is recommended to have a 1" ball valve on the outer drain line, so that the flow through the drain can be adjusted to allow a siphon to occur.  Once this ball valve is adjusted properly, you will have no problems with the external bell siphon working perfectly and continually.

Comment by Allisyn Wood on September 12, 2011 at 12:33pm


How does it kick on if the water is filling up inside the 1" outside stand pipe and spilling over into the 2" bell cover? How does the water get to the drain if there's a 90 degree elbow inside the 2" Tee that leads back to the tank or does it escape through the gap between the 2" male adapter that's screwed into the top of the Tee?  I can only assume this works in reverse of the "traditional" bell siphons?? I thought the bell had to fill up first then drain into the smaller pipe to create the suction required to pull the bell down and draw the water out quickly.


Have you been using this? Please let me know how it works for you.  it would be nice to save the space in the beds for plants and no worries about media getting in under the bell and messing the whole thing up.  If the bell is glued on, must be hard to service if necessary...  Do you find that the bulkhead gets clogged up easily? Is this even for a media bed or better for a raft?

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