Hydro-Brake® Flood flow controls are self-activating, relying on upstream hydraulic head to generate an air-filled vortex within the centre of the casing. This air-filled core occupies the majority of the outlet, restricting the flow.
The Hydro-Brake® Flood flow control moves through three distinct phases of operation:
Under low flow conditions the flow control behaves like an oversized orifice. The flow is gentle, with minimal turbulence inside the volute of the flow control or the outlet pipe. As the water level starts to increase 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 and the entrapped air forms the central core. At first there is not enough energy in the water flow to sustain a stable vortex, so the vortex will continually start to build and collapse.
The head at the end of this phase is the point at which there is sufficient energy within the flow to sustain a stable vortex.
A stable vortex is maintained within the flow control. High peripheral velocities around an 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, significantly reducing the risk of blockage.
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 an oversized orifice. This drains the system quickly and more effectively, so that the flood storage reservoir is ready for the next event.