OK, so for those of us who have built our own flood and drain Aquaponics or Hydroponics systems, we know the challenges that come with getting the Bell Siphon to work consistently and reliably. You just need to do a search on Youtube for " how to get your Bell Siphon to work" to see hundreds of possible fixes.
If the inflow rate into the grow bed is too slow, the bell siphon may not start the drain cycle or the fill cycle. Fill it too quickly and it may not stop the drain cycle.
Yes there are tricks that one can apply that will eventually get your backyard aquaponics bell siphon working properly, like adding a 90 degree bend to the bottom of the drain pipe, or ensuring a gradual reduction in the diameter of the outlet pipe...but what happens on larger commercial systems?
As we soon discovered when we built our two tunnel aquaponics commercial system, getting all 8 bell siphons on our flood and drain beds to work reliably and consistently is basically impossible.
Out of utter frustration, we decided to put the flood cycle on all our grow beds on a timer. We then started doing some research on possible alternatives and came across the Flout siphon. The Flout siphon is a great alternative for commercial aquaponics systems, the problem is that it is complex to build, takes a lot of space in the grow bed, and to retrofit existing bell siphon system, makes it impractical.
Still, we did not rest, we searched for a more practical and simpler solution.
We met with Willie Kok, an inventor of note in the fish pond and filtration industry in Johannesburg, South Africa. We explained our problems and within one week he came up with the VFS (Vertical Float Siphon) as per below:
Here the float of the VFS is resting at the bottom of the growbed, just before the initial water inflow
As the water starts flowing into the growbed the float rises accordingly
When the flow reaches its maximum float rate, as controlled by the length of the outflow pipe, water starts flowing over the lip of the float weighing it down and forcing it to the bottom of the grow bed
The water rushes down the outlet pipe at the centre of the float and out the two bottom exit holes at the bottom of the outlet pipe (refer to arrows).
Once the water drains to the bottom of the growbed and empties out of the inside of the float, the float starts rising again and another fill cycle begins
To video below will give a better perspective of how the VFS works