An automatic fog nozzle is a nozzle wich mantains a constant pressure over an ample range of gpm. The more popular in ebay are Akron's, Elkhart's and TFT's. All of them are from superb quality both on manufactutre an design.

What to look for?

The main advantage on using an auto nozzle is that there is not needing of communication between tha nozzleman and the pump operator, communication near impossible in the heath of a fire. For a nozzle operator the advantage of a flow (volume) control system never will be over emphasized. The best way for obtaining this is be means of a turbulence free valve. The only auto nozzles with that valve are TFT's, Protek's and Angus'. In fact one of the main and older nozzle manufacturer had to retreat from making auto nozzles because the fire depts do not like nozzles without flow control, and this nozzles manufacturer do not wish to pay the royalties involved (and implicit support to a better technology from a competitor) , so they make a spin explaining their retirement with strange wording.

The nozzles with ball valve do not permit to use it for volume control, in that case the result is a turbulent and disrupted stream, with low fire extintion capability.

Also look for big flush aperture, the bigger the better. The new way in fog nozzles is the selecting operative pressure knob and/or with pressures lower than 100psi.