The basic principle of multi-step spray systems is to be able to switch from one nozzle orifice size to another (usually larger) to increase the useful range of spraying speeds or application volumes when compared to a standard single line sprayer.

While the multi-step systems may offer the ability to increase spraying speed or application volume, increasing spraying speed must be carefully considered as this can increase drift potential and reduce penetration into canopies. More useful is a reduction in the minimum effective spraying speed, which can minimise overdosing, prevent spray quality from becoming too coarse at low pressure for some targets, and has the potential to reduce the size of headlands required.

To fully utilise two or more nozzles, the automatic rate controller (designed for multiple steps) must be programmed to know when the operator requires a switch or transition between one nozzle size to the next.

Depending on the type of rate controller used, the transition points may need to be entered into the rate controller as one of the following:

• pressure in the spray line, or pressure at the nozzle;

• flow rate of the nozzle, or flow rate through the whole boom (based on accurate section widths); or

• spraying speed for each transition.

The transition point that must be programmed into the rate controller for each nozzle will vary according to:

• the range of operating pressures for the specific nozzles chosen;

• the spray quality each nozzle produces; and

• the minimum pressure requirements of the next nozzle in the sequence of transitions.

Nozzle selection and the transition points between nozzles set in the controller are the most critical aspects to ensuring a multi-step nozzle system operates smoothly at the required spray quality.

Nozzle shut-off systems to turn nozzles on and off for the transitions

The commercially available multi-step systems utilise nozzle valves to turn the nozzles on and off. These are available as either electric nozzle shut-off valves, or air shut-off valves controlled by air solenoids. In both cases they offer almost instant switching and a positive shut-off. Switching the spray ‘on’ and ‘off’ at the nozzle provides the opportunity for boom recirculation systems to be used. This can prevent the operator from having to prime the boom in the paddock before they commence spraying.

Electric nozzle valves can also allow for nozzles to be controlled individually, which allows for single nozzle section control to be used. Typically, systems that use air shut-off valves have groups of nozzles plumbed together (the group is controlled by a single air solenoid) and are less likely to offer single nozzle section control.

When comparing the multi-step systems that use electric nozzle shut-off valves, it is important to consider the total current draw of the system that will occur for the width of the boom it is to be fitted to. Wider booms may present a problem for some nozzle shut-off valve types, particularly where multiple nozzles per outlet are fitted to the boom, or where narrow nozzle spacings are used.

Find out more

For more information on plumbing requirements for boom recirculation and nozzle shut-off valves go to Module 11: Pumps, plumbing and components