Self Governing SiphonI discovered this (new to me) strange siphon effect quite by chance. There is nothing new under the sun but I have not seen mention of this before.
What I have found?You can create a “self governing siphon” by simply placing a small hole (less than 1mm for airline) between where the tube meets the water and the apex.
With the siphon running a small amount of air is sucked in through the hole resulting in a mixture of air and water running through the tube. The faster the siphon runs the more air is sucked in. The more air is sucked in the slower the siphon runs. This is negative feedback..!
For any given rate of inflow (within limits) the siphon will eventually reach a state of equilibrium where the water level remains stable. In other words the siphon will remove water at exactly the same rate as the inflow.
To date I have only tried this with airline and 6mm drip irrigation tubing, although I see no reason why it shouldn't scale up to garden hose for example.
How can it be controlled?I need to do more experiments to confirm this but it seems moving the hole up or down in relation to the surface causes the water level to increase or decrease by roughly the same amount. Increasing the inflow will cause the level to rise until a new equilibrium is reached and vice versa.
There is a minimum rate of flow below which the siphon will stop and not restart even when the water rises again.
There is a maximum rate of flow above which the siphon cannot keep up with the inflow. The absolute fastest rate of flow is achieved when the level rises above the hole thus shutting of the air intake altogether.
So long as the inflow is constrained between these limits I have found the siphon to work very reliably. Never the less I have a small motor attached to the end of the siphons in my auto water change system so in the event the siphon stops for any reason the motor kicks in for 10 seconds after which the siphon is primed. A little more to it than that but you have the essence.