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Spray Distribution


How to evaluate spray deposits

Spray cards can be evaluated either by visual estimate, by counting the droplets under a lens, or by automatic image analyzers such as the Optomax V.

Visual assessment of spray distribution

For a quick assessment place the numbered papers in front of you. A glance will reveal overdosing or underdosing originating from either incorrect nozzle settings or malfunctioning. Recording the spray pattern makes it easier to identify and correct any of these deficiencies. For accurate assessment of droplet density, counting is still recommended.

Water-sensitve papers exposed to aqueous sprays

  • water-sensitive paper: overdosing (10Kb JPEG)
  • water-sensitive paper: overdosing (14Kb JPEG)
  • water-sensitive paper  (16Kb JPEG)
  • water-sensitive paper  (10Kb JPEG)
  • water-sensitive paper: underdosing (9Kb JPEG)
  • water-sensitive paper: underdosing (5Kb JPEG)

A quick glance reveals positions of overdosing [above, left] and underdosing [above, right].  And nozzle dripping.

0.8 ml/min 19 droplets/cm squared (5 Kb JPEG)
0.8 ml/min 19 droplets/cm squared
1.6 ml/min 31 droplets/cm squared (6 Kb JPEG)
1.6 ml/min 31 droplets/cm squared
3.2 ml/min 55 droplets/cm squared (7 Kb JPEG)
3.2 ml/min 55 droplets/cm squared

Droplet numbers produced with a spinning disk sprayer at 1800 rpm and 3 different flow rates (0.8, 1.6, 3.2 ml/min) producing a VMD* of 300 μm.

* Volume median diameter (half the spray volume consist of droplets smaller, and half of it larger than the VMD)

Visual assessment of droplet densities

Compare your spray samples with some known standard. The standard cards below cover the range of acceptable droplet densities for coarse and medium low volume spray. The droplet density in the target area should not be less than:

Numbers of droplets per cm2

Types of Spray

20 - 30

Insecticides

20 - 30

Herbicides pre-emergence

30 – 40

Contact herbicides pre-emergence

50 - 70

Fungicides

* 1 cm sq = 0.155 sq inch 1 sq inch = 6.452 cm sq

For routine checking of sprays you might also prepare your own standard cards by selecting spray cards with known droplet densities from previous spray operations.

Standard cards with a known droplet density per centimetre squared

Computer-plotted standard cards displaying the expected number and sizes cards spraying at 3 different volume rates (20, 30, 40 l/ha) and using 3 different droplet spectra (VMD, 200, 300, 400 μm) assuming waters sprayed and the spread factor is two.

VMD 200 μm

20 l/ha 129 droplets/cm sq (7 Kb JPEG)
20 l/ha 129 droplets/cm sq
30 l/ha 194 droplets/cm sq (7 Kb JPEG)
30 l/ha 194 droplets/cm sq
40 l/ha 258 droplets/cm sq (8 Kb JPEG)
40 l/ha 258 droplets/cm sq

 

VMD 300 μm

20 l/ha 38 droplets/cm sq (6 Kb JPEG)
20 l/ha 38 droplets/cm sq
30 l/ha 51 droplets/cm sq (6 Kb JPEG)
30 l/ha 51 droplets/cm sq
40 l/ha 76 droplets/cm sq (7 Kb JPEG)
40 l/ha 76 droplets/cm sq

 

VMD 400 μm

20 l/ha 16 droplets/cm sq (4 Kb JPEG)
20 l/ha 16 droplets/cm sq
30 l/ha 24 droplets/cm sq (5 Kb JPEG)
30 l/ha 24 droplets/cm sq
40 l/ha 32 droplets/cm sq (6 Kb JPEG)
40 l/ha 32 droplets/cm sq

Optical assessment of droplet densities

Linen tester lens together with the droplet counting aid card on an exposed collector paper. (13 Kb JPEG)
Linen tester lens together with the droplet counting aid card on an exposed collector paper.

For counting the droplets use a lens.

  • Place the lens at random on the collector at four different spots.
  • Count the number of droplets and record them.

After calculating the average number of droplets per cm sq of each water-sensitive paper/card, you then calculate the average droplet density for all the water-sensitive papers from a particular layout.

Water-sensitive papers are also suitable for processing in automatic image analyzers such as the Optomax V provided the droplet density is sufficiently small for the individual drops not to overlap with each other.

Optomax V automatic image analyzer processing collector papers (22 Kb JPEG)
Optomax V automatic image analyzer processing collector papers

 
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