11.2 Nozzle Types, Spray Patterns & Droplet Size Management

11.2 Nozzle Types, Spray Patterns & Droplet Size Management

Nozzles are the single most critical component of a hydraulic sprayer. They control liquid application volume, atomize liquid into a spectrum of droplets, and distribute droplets in a specific geometric pattern across the target area. Selecting the correct nozzle type, material, operating pressure, and boom height is essential for achieving effective pest control while preventing off-target spray drift.

Nozzle Types & Spray Patterns

Flat Fan (Tapered)       Even Flat Fan (E)        Hollow Cone             Solid (Full) Cone         Air-Induction (Venturi)
    /  |  \                 |  |  |  |              \   /                    /  |  \  \                 (Air-Filled Droplets)
   /   |   \                |  |  |  |               \ /                    /   |   \  \                 (O)  (O)  (O)  (O)
 (30-50% Overlap)       (Band Application)      (Outer Ring Spray)        (Uniform Circle)            (Low Drift Impact)

Standard Flat Fan Nozzles

• Pattern Geometry: Produces an elliptical flat spray pattern with tapered outer edges. The volume deposited is highest in the center of the pattern and gradually decreases toward the edges.
• Boom Setup: Because edges are tapered, standard flat fan nozzles must be mounted along a spray boom with a 30% to 50% pattern overlap between adjacent nozzles to achieve a uniform application rate across the field.
• Operating Pressure: Typically operated between 15 and 60 PSI. Used for broadcast applications of post-emergence herbicides, insecticides, and fungicides.

Even Flat Fan Nozzles (Designated "E")

• Pattern Geometry: Produces a flat fan spray pattern that deposits a completely uniform volume of liquid across its entire width, terminating in sharp, non-tapered edges.
• Boom Setup: Even flat fan nozzles must never be overlapped. They are engineered specifically for band applications over crop rows or along turf edges.
• Application: Used when applying herbicides in narrow bands over seed rows to treat weeds while leaving inter-row spaces untreated, reducing chemical costs.

Hollow Cone Nozzles

• Pattern Geometry: Deposits liquid in a circular ring pattern where all spray droplets are concentrated in the outer band, leaving no spray in the center.
• Droplet & Pressure Characteristics: Operates at higher pressures (40 to 100+ PSI), producing fine droplets that swirl in turbulent air streams.
• Application: Fine droplets provide excellent canopy penetration and complete leaf coverage on upper and lower foliage surfaces, making hollow cone nozzles ideal for foliar fungicides and insecticides in orchards, vegetables, and cotton.

Solid Cone (Full Cone) Nozzles

• Pattern Geometry: Produces a circular spray pattern that is completely filled with droplets throughout its internal area.
• Characteristics: Delivers larger droplets at medium to high pressures with higher total flow rates than hollow cone nozzles.
• Application: Ideal for high-volume foliar applications, soil-applied insecticides, and spot spraying where thorough surface wetting is required.

Flood Tip (Flooding Fan) Nozzles

• Pattern Geometry: Discharges liquid through a wide circular orifice onto a flat deflection surface, producing a wide-angle, flat spray pattern.
• Characteristics: Operates at low pressures (8 to 25 PSI), producing very large droplets with low drift potential.
• Application & Orientation: Mounted on booms at a 45-degree angle pointing downward and backward. Frequently used for applying high-volume liquid fertilizer-herbicide mixtures and pre-emergence herbicides.

Air-Induction / Venturi Nozzles

• Mechanism: Features an internal venturi jet that draws ambient air into the nozzle body, mixing air into the liquid stream before atomization.
• Droplet Behavior: Atomizes liquid into large, air-filled (bubble-like) droplets. Because of their large size and mass, these air-filled droplets resist wind drift. Upon impact with target foliage, the air bubbles collapse, causing droplets to splatter and spread rather than bounce off leaf surfaces.
• Application: Highly effective for post-emergence herbicide applications in wind-sensitive areas.

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Nozzle Materials & Wear Characteristics

Nozzle tips wear over time due to mechanical abrasion from suspended solid particles (wettable powders) and chemical corrosion. As orifice erosion occurs, flow rate increases, spray pattern distribution distorts, and droplet sizes shift.

Cleaning Rule: Never use wire, nails, pocket knives, or metal pins to clear clogged nozzle orifices. Metal tools scratch and permanently ruin engineered tip geometry. Always use a soft-bristle nylon nozzle brush or compressed air.

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Spray Angle, Boom Height & Nozzle Spacing

The spray angle formed by liquid exiting a nozzle tip determines the swath width produced at a given boom height. Standard nozzle spray angles are 65°, 80°, and 110°.

    65° Spray Angle                 80° Spray Angle                110° Spray Angle
       (High Boom)                   (Medium Boom)                   (Low Boom)
           \ /                            \   /                        \     /
            v                              v                            v
  [Requires High Boom Height]   [Moderate Boom Height]       [Lowest Boom Height - Low Drift]

• Geometric Principle: For a fixed nozzle spacing along a spray boom (e.g., 20 inches apart), wider spray angle nozzles (110°) produce a wider fan spread, allowing the spray boom to be positioned closer to the ground while maintaining the required 30% to 50% overlap.
• Drift Benefit: Lowering boom height significantly reduces wind velocity exposure, keeping droplets within calm ground-level air layers and dramatically reducing off-target drift.

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Droplet Size Spectrum & Drift Management

Volume Median Diameter (VMD)

Spray nozzles do not produce droplets of uniform size; they produce a spectrum of droplets ranging from microscopic mists to large drops. The Volume Median Diameter (VMD), measured in micrometers/microns ($μm$), is the standard metric for defining spray quality.

• VMD Definition: VMD represents the droplet diameter where 50% of the total spray volume consists of droplets smaller than the VMD value and 50% consists of droplets larger than the VMD value.

ASABE S572 Droplet Size Spectrum Classifications

Physics of Spray Drift & Operational Mitigation

• Drift Mechanics: Droplets under 150 to 200 $μm$ have low mass and fall very slowly. Crosswinds under 5 MPH or vertical air turbulence can carry fine droplets hundreds of yards downwind.
• Operational Drift Reduction Rules:
  1. Select Low-Drift Nozzles: Use air-induction (venturi) or drift-reduction flat fan nozzles that produce Coarse to Very Coarse droplet spectra.
  2. Lower Operating Pressure: Reducing system pressure decreases liquid velocity and increases average droplet size (higher pressure creates smaller droplets).
  3. Lower Boom Height: Use 110° wide-angle nozzles to position spray booms as close to the target canopy as possible.
  4. Avoid High Winds & Inversions: Never spray when wind speeds exceed 10 MPH or during surface temperature inversions (when warm air traps cool air and fine spray particles near the ground).
  5. Utilize Drift Control Adjuvants: Add polymer drift control agents to increase liquid viscosity and reduce fine droplet formation.