Sprayer servicing and calibration

I see many occasions where simple changes can improve the application of pesticide in a much safer and more cost effectively way.

Simple changes include correct boom height. This should be a minimum of 500mm above the target so, if spraying turf, that's 500mm above the ground. I often see sprayers with the boom at one metre or more high, which can increase drift by at least five times.

Nozzle selection is also crucial to correct application. There are still many sprayers equipped with standard flat fan nozzles which produce too much drift. Even when I've taken sprayers in for servicing, it's not uncommon to see different sized nozzles used across the boom. All nozzles are now colour coded for easy reference - no matter which brand you buy the colours are all ISO standard and the outputs are the same - but never mix different brands as the spray quality may be different.

Always read the pesticide label to decide application rate, water volume and spray quality. On sports turf, most products will be applied at medium quality spray in 200-400 litres of water per hectare, which means you could, theoretically, use just one type of nozzle - a red 03 air inclusion nozzle. At just over 2 bar pressure and 8kmh forward speed, this will be ideal for spraying fairways at 200 litres per hectare with a tractor, not too fast so your booms are bouncing up, down and backwards and forwards, and not too slow so you can get the job done. The same nozzle at the same pressure, but with the tractor set to 4kmh, will be ideal for 400 litres per hectare, usually applying fungicides to greens for example. This is a nice steady speed for accurate spraying of small areas.

There are many air inclusion nozzles available and at 2 bar pressure for an 03 nozzle they will probably be 3 star lerap rated, the highest level of drift control. Drift will be minimal and, as long as boom height is kept around 500mm, there's no reason why spraying can't be done on most reasonable days.

Forward speed is another area that is flawed; with many operators relying on the tractor readout for their forward speed. This should be used as an estimate. To set the tractor up at the correct speed, you should rely on your rev counter as your guide. For example, say we want to set the tractor to do 8kmh whilst spraying, you need enough revs to power the tractor and pump, not too high so the tractor is over revving and not too low so the tractor struggles up hill and inclines. Then, select the correct gear that is nearest 8kmh and, say, 1800 rpm engine speed. Mark a track 100 metres long, preferably on the fairway, and time how long it takes to cover the 100 metres at the set engine revs and gears, use the hand throttle to set the revs, not your foot. Start to drive before and after the markers and set your times when you pass the marker. Record the time, and then return the other way, doing the same. You now have two times in seconds, add them together and divide by 2. For 8kmh you need 45 seconds to travel 100 metres. For 4kmh you need 90 seconds. Change the gears and revs slightly to get as near as possible. It's not a problem if it's not exact, as we can allow for it when we calibrate the sprayer.

The speed calibration formula is 360 divided by the time in seconds it takes to travel 100 metres, this gives you your kmh forward speed.

Now for calibrating the sprayer. Assuming 200 litres per hectare at 8kmh using red 03 nozzles, we need to do some simple tests first. Fill the tank with clean water, open the booms out, start the sprayer and set the same rpm used for setting the tractor speed, say 1800rpm. Set the pressure control to 2 bars, check for leaks and drips and repair accordingly.

When you measure the output of the first nozzle adjust the pressure so you get 1.33 litres per minute, then go on to measure the output of all the other nozzles. They should all be the same, give or take 5% variation - that's 1.27 lpm-1.39 lpm. Anything greater or less then the nozzle should be discarded and replaced with a new one.

The sprayer calibration formula is application volume x nozzle width x forward speed divided by 600, which gives you LPM per nozzle. In this example we said 200 x .5 x 8kmh /600 = 1.33 LPM

Record all the information for future reference. Remember, if you use a different tractor, you will need to calibrate the speed every time you go out to spray. Just check 2 or 3 nozzles for output. It should be the same, 1.33 litres per minute, just in case somebody has accidently turned the control knob. Do not rely on the pressure dial readout, always do a timed measure into a jug, the pressure clock is there as a guide only just like your tractor speedo.

When spraying, have the tractor moving at the correct speed before you turn the sprayer on. Do not adjust your forward speed or the rpm, or the pressure at which you calibrated. Do not make sharp turns whilst spraying, as this will under dose the outer side and considerably overdose the inside of the turn. Do not leave unsprayed solution in the sprayer overnight, or at lunchtime, as it may settle out of suspension. Always flush out the sprayer with clean water onto an area of grass not previously treated, not static but whilst moving.

Before winter always drain and flush through with antifreeze, remembering to flush out with clean water before you use it next.

Covered booms have their place but, personally, I have tried them and, apart from a small two metre one I use for spraying ornamental areas, I see no advantage with them as nozzle technology has become more advanced.

On a golf course, if you are doing your own spraying, you will have a choice of days to spray and, if you start early enough, wind is not usually a problem, even on some links courses. The correct forward speed, the right nozzle and the correct boom height will go a long way to more effective spraying, without the expense of a covered boom.

When having your sprayer serviced, always ask for the latest low drift nozzles and multi-nozzle holders to be fitted. I cannot see a need for more than three different nozzles and, possibly, only one would be needed on a golf course.

Have the sprayer matched to the tractor, calibrating the forward speed and adjusting the sprayer accordingly. A printed document should be given to the head greenkeeper/groundsman as an easy reference of different application rates and which nozzles and forward speed to use.

As well as nozzles, new filters, triplet nozzle holders (if not already fitted), pump overhaul and replacement of all seals and O rings should be included in the service. Have the PTO shaft and cover replaced or repaired.

The machine should also be fully cleaned inside and out, and drained, as most service centres will not take in contaminated sprayers.

Richard Rainford can be contacted on 07711004000 or email richard@rainford.com