Pulse width modulation sprayers: what we have learnt, correct operation and looking ahead

Published: 1 Apr 2019

GRDC Pulse width modulation sprayers cover image

What is pulse width modulation?

Pulse width modulation (PWM) is a spraying system where the flow rate is controlled by a pulsing solenoid at each nozzle, unlike a standard spray system that directly controls the overall flow rate. Learn more on page 1 of this factsheet.

Key points

Pulse width modulation (PWM) sprayers are continuing to improve with new technology providing more consistent performance, individual section control and turn compensation
Constant pressure maintains droplet size and spray quality over a range of speeds
Low duty cycle operation can result in poor coverage especially with 10Hz systems
Newer systems have high cycle frequency (15/30/100Hz) and combine other standalone spraying systems
There are many misconceptions about the effective working speed range, correct nozzle size and determining the correct pre-set pressure
When set-up and operated correctly PWM sprayers perform accurately

Frequently asked questions

How many sets of nozzles are needed?

Can my PWM sprayer conform with the new 2,4-D VC spray quality permit requirements?

Yes, there are several options. Wilger has a specialised range of pre-orifice nozzles (MR, DR or UR types) that are designed for producing large droplets (VC, XC, UC spray qualities) and for droplet-drift management. The UR series is relatively new, producing ‘ultra-coarse’ droplets, one of the coarsest spray tips in the world designed for highly sensitive areas. The ARAG TDFL nozzle also conforms with these requirements.

What is the process for selecting the right nozzle?

First determine the flow rate required based on working speed and water volume by using a standard nozzle flow rate chart. Select nozzle size and 100 percent duty cycle pressure. The sprayer will need to be operated at pressures ‘slightly higher’ so t is now working at 100 percent duty cycle. This will then allow the selection of a suitable nozzle that gives the desired spray quality based on these higher pressures. The GRDC 2019 PWM Nozzle Selection Guide references duty cycle for water rate and working speed, and nozzle selection options.

What does increasing pre-set pressure do to duty cycle?

Topics covered in this factsheet

Duty cycle frequency
Duty cycle percentage
checking coverage and skips with water-sensitive paper
PWM nozzle size selection process
Types of PWM nozzles
PWM nozzles available for 2,4-D application
Can air-induction nozzles be used?
Larger droplets with PWM
Travel distance, pulse frequency and duty cycle interaction
PWM hardware and application accuracy

Download PDF

Pulse width modulation sprayers: what we have learnt, correct operation and looking ahead (PDF 414.8 KB)

Region: National

Was this page helpful?

YOUR FEEDBACK

To protect your privacy, please do not include contact information in your feedback. If you would like a response, please contact us.