Choosing a nozzle type

As the pressurised spray mix comes out of the nozzle it forms a sheet of liquid. This sheet gets thinner and thinner as it widens out, before breaking up into drops. The width of the footprint of these drops on the ground and the spread of the drops within the footprint, are controlled by the design of the nozzle.

The size of, and pressure of the liquid at, the nozzle opening, control the flow rate (L/minute). The speed at which you spray then determines the spray mix volume rate that you apply.

The design of the nozzle and the pressure at the nozzle opening also combine to produce smaller or larger drops of spray. For example at the same pressure, hollow cone nozzles produce smaller drops than deflector nozzles. This means that for nozzles producing larger drops there will be fewer drops to cover the target surface and for nozzle producing smaller drops there will be more drops to cover the target surface.

Each single nozzle can produce a range of flow rates and hence volume rates. The nozzle size (e.g. 03 Blue, 02E) that will produce the combination of drop size and volume rate that you need is a function of:

• the size of the nozzle orifice
• the pressure at the nozzle orifice
• the operator's walking speed.

Drop size can affect both how well the drop reaches and remains on a target surface and the cover of pesticide drops over the target surface. It can also affect your safety and that of your enviroment.

Terms used for drop size

The terms often used for drop size are:

Make sure that you space your nozzle correctly so that you:

• apply the right amount of spray mix
• get a uniform spread of spray drops.

Spray width, swath width and nozzle spacing