Part 8: Notes for air atomising nozzles 

The discussion so far has been confined to hydraulic nozzles. Hydraulic nozzles rely entirely on the internal energy of the fluid being sprayed to break it apart into droplets and form the spray pattern. Air atomising nozzles, on the other hand, impact compressed air onto the fluid to break it apart and form the pattern.

(For details on the working principles of air atomising nozzles please visit this section of our web site here)

The introduction of a secondary source of energy into the system changes the rules outlined above completely.

Droplet size

The level of atomisation is no longer primarily a function of liquid pressure and pattern type (although these still do have some effect).  Rather it is almost entirely down to the amount of air being used. The higher the air pressure and flow rate the smaller the droplets will be. This means that even very low flow rates at low fluid pressures can be finely atomised.

 

Impact and reach

Air atomising nozzles will always produce very fine droplets and so will be low impact, but the reach of these fine sprays can be greatly enhanced with the presence of air. Hydraulic misting nozzles will have used up most of the internal energy of the fluid being sprayed to break it apart leaving little for projecting the fluid forwards. This means that fine sprays from hydraulic nozzles will have a very small forward projection before they are at the mercy of air currents. Not so with air atomising nozzles. The compressed air from such nozzles can be used to help project even very fine spray over many metres.

Liquid distribution

As air atomising nozzles produce very fine droplets the distribution of fluid is generally very even (see above). Furthermore, the air is used to shape the pattern rather than the centrifugal forces in a hydraulic nozzle. This means there is far less opportunity for bigger droplets to concentrate in centrifugal rings.  

Next: Part 9 Conclusions 


Guide to spray properties