Farm Ireland

Thursday 18 January 2018

Calibration vital to spray success

Check nozzles and pressures for a consistent chemical spread on crops

Teagasc's Tom Ryan checks sprayer nozzle calibration at Kildalton Agri College, Co Kilkenny
Teagasc's Tom Ryan checks sprayer nozzle calibration at Kildalton Agri College, Co Kilkenny
ISO nozzles are colour coded to make them and application rates easy to identify
The pressure gauge could be fautly if newly installed nozzles fail to match the recommended pressures in the chart
A nozzle test has to be performed in a clean sprayer

Bruce Lett

Sprayer nozzles do wear with use over time and they are the first things to consider about sprayer calibration. What is their output at a given pressure?

A number of years ago, sprayer nozzles were standardised through the International Standards Organisation. This makes them simpler to identify and use -- red jet, red cap, blue jet, blue cap and so on.

The nozzles' capacity is also proportional to the nozzle size -- for example an 02 nozzle at three-bar pressure has an output of 0.80 litres/min, while an 04 nozzle at the same pressure has double the output at 1.6 litres/min.

The Teagasc table (right) demonstrates this but be aware: there may be a few old jets still out there.

Nozzle check

Fan pattern nozzles, such as those in the chart above, are, for the most part, the most common type of spray nozzle used here and are what we will concentrate on in this article.

Armed with the ISO fan nozzle information and a graduated jug or similar, it is possible to check the output of each and every nozzle on your sprayer. This is certainly a worthwhile exercise because a sprayer might put out the correct amount of chemical over a given area but may not have applied it evenly across the width of the boom if there were nozzles more worn than others. This would not be known until too late and could have a serious effect on the crop's growth and yield.

Before checking nozzle outputs, it's worth ensuring that you have on appropriate personal protective equipment, gloves, overalls, etc.

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A nozzle test is performed with clean water in a clean sprayer but there may still be spray residues on boom or tank surfaces, so it is better to be safe.

With the jug in one hand and stopwatch or other timing device -- many mobile phones have a stop watch -- in the other, select a pressure to run the nozzle test at.

As an example, from the ISO chart, a red 04 nozzle run at three-bar should have a output of 1.6 litres/min.

Over a quarter of a minute (15 seconds) it would have an output of 400ml. This can be checked (and recorded) for each nozzle.

Teagasc's Tom Ryan advises that the output of each jet should be within 10pc of the average output of the set. If they are not, first check that they are all the same size, and that the nozzle and filter are clean. If that does not solve the problem, a new set is needed.

He also says the average output of the jets should be within 10pc of the figure in the chart.

If the difference is bigger, then one of two things is wrong -- the pressure gauge is reading wrong, or the nozzles are worn.

Before you replace all the nozzles, though, he recommends you fit three new nozzles on the sprayer and measure their outputs. If they still do not tally with the chart, then the sprayer's pressure gauge is not reading properly. Fit a new gauge and start again.

Indo Farming