Mixing apparatus assembly with air gap separation, in particular for backflow prevention

This invention relates to a mixing apparatus assembly with air gap separation, comprising a first duct, having an inlet mouth and a diameter D, connected to an air gap valve downstream of which a venturi mixing device is connected, the air gap valve comprising a nozzle having an outlet spaced apart by a separation distance from a collecting duct, the first duct and the air gap valve forming a linear channel upstream of the outlet of the nozzle, going from the inlet mouth of the first duct to the outlet of the nozzle and having a length L, the assembly being characterized in that the length L being not shorter than D and not longer than 20D, i.e. D≦L≦20D, and in that said linear channel is provided with a flow straightener. This invention further relates to an apparatus for mixing a liquid comprising such assembly.