ISO 25358:2018

Overview

ISO 25358:2018 - "Crop protection equipment - Droplet-size spectra from atomizers - Measurement and classification" specifies procedures for measuring and classifying droplet-size spectra produced by atomizers used in crop protection spraying. The standard provides a reference system of reference droplet size spectra (reference sprays and nozzle/pressure combinations) to enable relative comparison of results obtained from different measuring systems and laboratories.

Key topics and technical requirements

• Scope: Classification of droplet size spectra using reference spectra; intended to harmonize terminology and relative comparisons across instruments.
• Reference spectra and nozzles: Defines boundary spectra using specified reference nozzle/flow rate (pressure) combinations (see Table 1 in the standard - e.g., Mee Fog IP‑16 and various TeeJet models).
• Measurement parameters reported: Characteristic diameters Dv0.1, Dv0.5 (volume median diameter), and Dv0.9 (10%, 50%, 90% cumulative volume points).
• Sampling and measurement:
  • Use at least three candidate atomizers from a batch of ≥10 with flow deviation ±3% of manufacturer rating.
  • Representative cross‑sectional sampling of the spray plume at typically 30–50 cm from nozzle (or appropriate distance for full atomization).
  • Recommended environmental conditions for inter‑laboratory comparison: spray liquid and air at (20 ± 2) °C, relative humidity 40–80%.
• Instruments: Accepts non‑intrusive methods appropriate for the droplet size range and liquid (e.g., phase Doppler, laser diffraction, imaging, single‑particle counters). Instrument configuration and calibration must be verified.
• Precision and calibration:
  • Repeatability targets (example): maximum deviations between replicates for Dv0.5 of ±10%; laser diffraction replicates often required <±5% for some parameters.
  • Flow measurement accuracy of at least ±1%; atomizer output stability within ±2.5% during measurements.
• Classification rule: Compare measured droplet spectrum to reference spectra; classify based on whether Dv0.1, Dv0.5, Dv0.9 fall between boundary spectra parameters.

Applications and who uses it

• Agricultural equipment manufacturers validating nozzle and atomizer performance.
• Test laboratories and calibration facilities performing droplet sizing and inter‑lab comparisons.
• Regulatory bodies and researchers concerned with spray drift management, pesticide application efficacy and environmental risk assessments.
• Growers and crop protection advisors seeking standardized information about spray quality and droplet size classes.

Related standards

• ISO 5681 - Equipment for crop protection: Vocabulary
• ISO 5682-1 - Spraying equipment: Test methods for sprayer nozzles

ISO 25358:2018 helps ensure consistent, comparable droplet‑size reporting across instruments and labs - supporting better decision‑making for spray application, drift mitigation and equipment certification.