Quote Originally Posted by keith_r
not really,, if you want a constant flood, you still need the water to come up to a level that will be usable to plants.. so if you put a hole on the bottom of the grow bed, put a fitting in it, and make a standpipe so that the water level is 3 or 4" below the surface of the gravel, you can just be always pumping, no siphon to worry about, you could make a couple different size standpipes as well.. when you first put your seeds in, you'll want the water to come up to maybe 1" below the gravel surface..
just put some kind of guard around the standpipe so that you can clear roots or change out the pipe easily
Now take a mason jar and place it upside down over the stand pipe. Make sure there is no gravel inside it. Place the jar so its opening is about one or two inches above the bottom of the grow bed. This can only be done if the stand pipe is about the same height as the mason jar is deep. Make sure there is one inch or more between the top of the stand pipe (now inside the upside down jar) and the jar's bottom. This allows the water to flow unimpeded by the bottom of the upside down jar.

You have just created a bell siphon. The bell is the upside down mason jar.

To improve on the range of flood and drain times, add a funnel (usually a pipe reducer) to the top of the stand pipe (courtesy of Affnan), keeping the total height about one inch below the level of the top of the grow bed media and the bottom of the upside down mason (or whatever) jar.

The diameter of the stand pipe is important, for it will determine the range of possible siphon times. The flow into the grow bed must match that range in order for the siphon to work. To little flow and the siphon won't start. Too much flow and the siphon won't break, causing the grow bed not to fill.

For a forty to seventy gallon media (Hydroton) filled grow bed, I have found that a half inch diameter stand pipe is optimum for a fifteen minute cycle time.

When determining the size of your standpipe based on the above numbers, remember that cross sectional area of the standpipe is a square of the diameter. For example, a three quarter inch standpipe will drain a grow bed in about half the time as a half inch diameter standpipe and will need twice the minimum grow bed inflow for the siphon action to start.

Oliver