Pro Operator

Giving NSTS some stick – Spring 2020 edition

Trevor Johnson, NSTS tester

Since the implementation of the sustainable use directive, additional elements have been added to the NSTS test to comply with regulations. To make sprayer testing more accurate and efficient, one tester has developed a memory stick laden with useful criteria. Geoff Ashcroft reports.

Amendments to the NSTS test have seen additional mandatory items included for crop sprayer testing.

“There’s a host of additional test requirements, including a minimum pressure gauge diameter of 63mm; working pressures must be stable within +/- 10%; nozzle orientation must be within +/- 10° of vertical and induction hoppers must be fitted with a grid to prevent any object larger than 20mm passing into the spray tank,” explains Norwich-based NSTS tester Trevor Johnson of Acare Services.

“Extra checking adds time and complexity, and it can also build in more margin for error – particularly when you need to start calculating boom straightness and sag.”

To simplify test procedures, and make many tasks quicker, more efficient and indisputable, Trevor looked at ways to make the criteria much more practical for him to implement.

“I wanted to speed up some of the processes but without compromising on accuracy,” he says. “So, I decided to create a ‘memory stick’ that carried all the mandatory criteria for sprayer testing, which I could use as an instant reference tool. My prototype was a one-metre long piece of 3/4in timber, fitted with markings.”

Sprayer gauge

63mm blue strip on the memory stick is the minimum diameter for pressure gauges. Analogue gauges must show maximum 0.2 bar increments from zero to 5 bar, then no larger than one bar increments from 5-20 bar.

Boom yaw

With a string line pulled from the centre section, this 24m boom can be within +/- 30cm of the string line, to remain within tolerance to pass the NSTS test. The memory stick shows this tolerance with a red line.

Boom yaw out

Excessive play or damage to the boom could see its resting position exceed the NSTS tolerance on fore/aft movement – with the measurement exceeding the datum line. The memory stick’s markings remove all doubt without needing to make calculations.

induction hopper

Induction hoppers must be fitted with a grid, to prevent objects larger than 20mm passing through to the spray tank. Using the memory stick’s 20mm ball eliminates the need to put hands inside the hopper to check grid size.

nozzle height

Consistent nozzle height tolerance is within 1% of half the boom width, measured across the full width – but what is the measurement?  Using a string line across the bottom of the boom, nozzle height variation is easily checked by referencing the corresponding zone.

Nozzle orientation

All nozzles must now be within +/- 10° of vertical, and this is easy to exceed if repairs have been hurriedly carried out. But how do you measure that angle? Trevor Johnson has thought of that too, adding markings to one side of the memory stick.

nozzle spacings

Nozzles must be positioned at consistent spacings across the boom width and be within +/- 5% of their nominal distance. Where spray line sections end, mis-adjustment can occur – easy to rectify with the memory stick, with zones for 25cm, 33cm and 50cm nozzle spacing.

nozzle flow

Nozzle flow rates must be within +/- 10% of manufacturer’s data, at your typical working pressure. And all nozzle sizes fitted to the boom must also be checked. No trouble remembering the tolerance when carrying out a jug test for each nozzle.

nozzle types

With the exception of special function nozzles, all those in use must be the same type, material size and from the same manufacturer. It might seem obvious, but having it stamped on the memory stick is a useful reminder.

spray pressure

Pressure balance must meet the prescribed tolerances. Pressure pulsations when raising and lowering line pressure must remain within +/- 10%; and there must be a uniform pressure across the boom width – also within +/- 10% of the average.

flow rate

If a sprayer is fitted with an electronic auto-rate controller, its total flow check must be within +/- 10%, defined by average nozzle output multiplied by number of nozzles. Forward speed must be cross-checked and be within +/- 5%.

tray test

Trevor Johnsons’ implementation of simple ideas has also seen him develop a portable fertiliser measuring rig into which tray contents can be tipped. “This makes it easy to see a pattern, when checking the co-efficient of variation,” he says.

Trevor Johnson’s NSTS memory stick has been so well received by the industry, that he will produce them for operators, at a cost of £45 +VAT. The ‘memory stick’ also earned him second prize in the Normac show’s new ideas award. “It’s not definitive, and if operators know of better ways to simplify test procedures, then we’ll all benefit from sharing ideas.”

You can contact Trevor by heading to his website contact page, HERE at Acare Services.

You can ring him on 07909 997590

Or email him direct at

Top 10 most common failures

1 – Leaking DCVs

2 – Leaks when spraying

3 – Leaks when static

4 – Tank sight gauge

5 – Hose condition

6 – Induction system leaks

7 – Boom not straight

8 – Pressure gauge accuracy

9 – Leaks with nozzles turned off

10 – Guards


Did you know? In 2018, 53% of crop sprayers now pass their NSTS test first time, without needing any additional work. This compares with 50% in 2017, and 46% in 2016.

To download a PDF of the NRoSO record sheet, click HERE   and the check list can be downloaded HERE


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