Under low flow conditions the flow control behaves like a large orifice.
The flow is gentle, with minimal turbulence inside the volute of the flow or the outlet pipe.
As the water level increases above the soffit of the outlet air becomes trapped in the volute.
This exerts a back pressure against the water and begins to restrict the cross-sectional area available for water flow.
As the water depth continues to increase, a vortex begins to form within the unit...
...with the entrapped air forming the central core.
At this point a stable vortex is maintained within the flow control.
High peripheral velocities around the aerated core create a back pressure...
...which effectively chokes the flow through the outlet aperture.
Following initiation of the vortex the flow control restricts the flow in a similar fashion to an orifice...
...but with clear openings up to 600% larger.
This significantly reduces the risk of blockage.
Hydrodynamic vortices such as this effectively manage water quantity and can prevent flooding.
The vortex maintains itself for as long as flow continues...
...with no moving parts and no power input required.
As the water level subsides, the energy within the flow reduces and the vortex collapses.
Air is drawn into the volute and the flow control returns to operating in a similar manner to a large orifice.
