What is an Auto-Siphon?
An autosiphon is simply a siphon that can start and stop itself in response to changing water levels. They are used to control the Flood and Drain cycles in a growbed. There are two implementations that are currently being used in aquaponics: a Looped Autosiphon, and a Bell Autosiphon. We have decided to use a Bell siphon.

The bell autosiphon consists of 1. A vertical standpipe inside the growbed extending through the base of the growbed, 2. A larger pipe (siphon pipe) placed over the standpipe. The siphon pipe is freestanding and taller than the standpipe, and is fitted with an endcap. Additionally, the base has pieces cut out to allow free movement of water. 3. A small air tube to assist in breaking the siphon when the water level has dropped low enough. 4. We have also used a third larger Pipe with many holes drilled in it. This pipe allows for easy cleaning out of roots and debris, as well as a way to keep the gravel from clogging the intake slots at the bottom of the siphon pipe.
Water flows up between the walls of both pipes then down the inside of the stand pipe, creating the siphon. When the water level drops to the intake end of the air tube, the siphon is broken. Here are some pics of our Auto-Siphon:

DSC00816.JPG An Arial Shot of our Auto-Siphon

DSC00817.JPG An Arial Shot of our Auto-Siphon with the Siphon tube removed. This verticle standpipe passes through the bottom of the growbed and emptys into the fish tank.

DSC00818.JPG Here's the Siphon Pipe by itself. Notice the slots in the bottom for water intake.

Here's a video of the Autosiphon going to siphon and then breaking the siphon: