Past FSOOTY winner, Stuart Woods, has carried out numerous field trials with his Pulse Width Modulation (PWM) system to determine the optimum settings for his chosen nozzles.
As one of the first Pulse Width Modulation (PWM) users in the UK, Stuart Woods didn’t have the benefit of others’ experience to help him with the settings for this cutting-edge technology. So, during the past two years, he has tested numerous nozzles and settings to optimise his applications.
The system is fitted to a three-year old Bateman RB55, with 5,600-litre tank and 36m wide, VG boom, he operates for K+MJ Atwood Ltd, Hempstead Farm, Sittingbourne, Kent. Here he covers about 1,200ha of mainly combinable crops including wheat, spring barley, oilseed rape and beans.
Probably the biggest PWM learning curve has been finding the best nozzles. “I did know normal air induction nozzles don’t work with PWM, due to the venturi breaking down because the flow is switched on/off. So that meant the end of the road for my trusty GuardianAirs, which had until then been my go-to nozzles for most work,” he says.
The GuardianAirs (GA), however, became his benchmark against which all potential replacements are assessed.
“An 03 GA applying 100-120 litre/ha at 3 bar creates a coarse droplet, about 330 micron in size. The alternatives are all pre-orifice designs, which are quite commonly used with PWM in the USA,” he says.
Stuart had to practically teach himself how to use, set-up and get the best from the PWM system. Although he was in touch with Bateman who put him in contact with Brian Finstron, from the manufacturer Capstan, as well as Wilger nozzles in the USA.
“I test all the nozzles in the field at a range of pressure, speeds and PWM Duty Cycles (the % of time the nozzle is on/off). I assess this with water sensitive paper and, after a while, realised that each nozzle has a ‘sweet spot’ where all the operating parameters meet to provide the optimum application. And that never changes,” he explains.
PWM nozzle choice
For finer work – insecticides and pre-ems in good conditions – he chooses to use an 05, Defy 3D at 120-200 litre/ha with its sweet spot at 2.1 bar, where it makes ‘medium’ – about 280 micron drops. “I changed from an 04 to an 05 because the bigger size gave me a more flexible range due to the speed and Duty Cycle restrictions. These nozzles are best used at lower pressures. Also the nozzle has a 2* rating at 0.7 bar – which PWM can hold if needed (100% DC),” he says.
For drift control he switches to a Pentair LDM (Low Drift Max) 06. It produces coarse to very coarse droplets. “It has a pre-orifice with a double hole and I’ve found it makes 500 micron droplets at 2 bar and 11km/h, but will work up to 6 bar. It’s actually sold as a John Deere nozzle in the USA and I was sent it to try by Roger James from Pentair, who has been very helpful,” adds Stuart.
Stuart’s main choice for fungicides and glyphosate is the Wilger MR04, which replaced the GuardianAirs. Again another nozzle popular for PWM in the USA it’s available from Bateman, Cleveland Crop Sprayers and SLY Agri in the UK.
“Wilger has been very helpful and has very good resources and nozzle charts online. I use the MR04 at anywhere between 2-6 bar and will increase pressure to get the droplet size I want. It also has a 3* rating at sensible pressures of 1 to 2.5 bar (at 100% DC),” he adds.
What about LERAPs?
As well as not being able to use air induction (low drift) nozzles for PWM it’s difficult to use for LERAPS.
“This is because there are no nozzles with LERAP ratings to use with PWM, due to lack of testing. This is a huge grey area, which affects every system. But work is in progress. However, a conventional GuardianAir has a 3* rating at 1.5 bar, which a conventional sprayer would struggle to maintain. But you set that on PWM and it will not fluctuate, although PWM must be set to 100% Duty Cycle – which means it is off.
“I prefer to use the MR04 at 2.5 bar to achieve a 3* rating. In fact Wilger offers eight sets of nozzles ranging from 2* to 4* ratings,” explains Stuart.
“There is a real need to start getting some LERAP testing done for nozzles for use with PWM. We need an agreement for a frequency, say 10Hz at a DC of 50% to allow for turn compensation within these parameters. Currently we are having to spray around vulnerable areas without PWM. That can cause over-dosing – which turn compensation prevents – and that doesn’t make sense,” he adds.
Turn compensation works well, he says, automatically reducing the flow on the inside, while increasing it on the outside of the boom, which is turning much faster.
“Slight bends and corners are breeding grounds for weeds, as well as increase the risk of resistance because they previously did not receive the full dose. Now 100% of the product is delivered across the whole boom and in three years there has been a noticeable improvement in control, with no scorch on the insides.
“Point source pollution is cut using PWM, eliminating over-dosing on bends next to water courses. Single nozzle control means there’s very little overlap on the ins and outs and far less over-dosing, which also cuts point source pollution,” he adds.
Reliability-wise Stuart reports no problems. “I have never had to change a solenoid in three years. I am quite particular about sprayer cleaning and hygiene, but the solenoids still look like new,” he comments.
Levelling for the Bateman 36m, VG boom is provided by the Norac system, originally controlled by its own software. Recently Stuart has upgraded to using Bateman’s updated BBL software. “It’s a low-cost upgrade, but has brought a huge improvement in how the boom reacts. I used to lift the booms at the ends to prevent the risk of damage – but don’t need to do that now,” he remarks.
|Sprayer: Bateman RB55|
|Boom: 36m Bateman VG|
|Sections: Individual nozzles|
|Nozzle spacing: 50cm|
05, Defy 3D
06, Pentair LDM
04, Wilger MR04
|Control: PWM – Capstan PinPoint II|
|Levelling: Norac with Bateman BBL control|
|Lights: Comatra blue|
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