5.3 Spraying Equipment, Nozzles & Chemigation Safety

Pesticide Application Equipment Overview

Selecting, operating, and maintaining correct application machinery is necessary to deliver pesticide active ingredients uniformly to target sites while preventing off-target drift and chemical waste. Application machinery varies in scale and engineering complexity based on target crop, topography, pest biology, and carrier volume requirements.

Primary Equipment Types

1. Low-Pressure Hydraulic Boom Sprayers:

   • Operating Principle: Utilizes a positive displacement or centrifugal pump to pressurize liquid spray mix (typically 20 to 60 PSI) and deliver it through evenly spaced nozzles along a structural boom.
   • Primary Uses: Broadcast application of herbicides, insecticides, and fungicides on field crops, pastures, turfgrass, and rights-of-way.
   • Core Components: Polyethylene or stainless steel spray tank, mechanical or hydraulic agitation system, line strainers, pressure regulator, pressure gauge, boom control valves, and nozzles.

2. Backpack & Small Capacity Sprayers:

   • Operating Principle: Hand-pumped lever or battery-driven electric pump pressurizes a 3 to 5 gallon tank, delivering spray through a hand-held wand.
   • Primary Uses: Spot treatments, structural perimeter sprays, noxious weed control in inaccessible terrain, and greenhouse applications.
   • Calibration Nuances: Operating speed and wand motion are controlled manually by the operator, requiring careful walking rhythm to maintain uniform coverage.

3. Airblast Sprayers (Air-Assisted Rig):

   • Operating Principle: High-pressure hydraulic pump delivers liquid spray to nozzles positioned in a radial pattern in front of a powerful axial fan. The high-velocity airstream atomizes liquid into fine droplets and transports them into dense crop canopies.
   • Primary Uses: Tree fruit orchards, vineyards, and tall timber plantations.
   • Drift Hazards: High air velocities create substantial off-target drift and atmospheric inversion risks if operated during windy conditions or improper temperature profiles.

4. Mist Blowers & Foggers:

   • Operating Principle: Generates ultra-fine liquid droplets (<50 microns) using high-speed air turbines or thermal heat generators.
   • Primary Uses: Mosquito vector control, greenhouse fumigation, and insect control in storage facilities.

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Spray Nozzles: Orifice Materials & Wear Resistance

The spray nozzle is the single most critical component on application machinery. Nozzles perform three primary functions:

1. Meter the volume of spray solution delivered per minute (GPM).
2. Atomize the liquid stream into a specific range of droplet sizes.
3. Form the spatial pattern of droplet distribution.

+---------------------------------------------------------------------------------------+
|                           NOZZLE MATERIAL WEAR RESISTANCE                             | 
|                                                                                       |
|  Material                  Relative Wear Life     Abrasive Resistance    Cost         |
|  --------                  ------------------     -------------------    ----         |
|  Ceramic                   100 to 200 (Highest)   Extreme                High         |
|  Hardened Stainless Steel  20 to 30               Excellent              Moderate     |
|  Stainless Steel           10 to 15               Good                   Moderate     |
|  Molded Polymer / Plastic  4 to 6                 Moderate               Low          |
|  Brass                     1 (Fastest Wear)       Poor                   Low          |
+---------------------------------------------------------------------------------------+

Nozzle Material Evaluation

• Ceramic: Highly resistant to abrasive minerals and corrosive formulations. Ceramic orifices maintain precise flow rates and spray pattern integrity over hundreds of hours of use with Wettable Powders (WP) and Dry Flowables (DF). Highest initial cost, but lowest long-term cost.
• Hardened Stainless Steel: Excellent resistance to wear and physical impact. Recommended for high-acreage commercial operations spraying abrasive suspensions.
• Stainless Steel: Good overall chemical and abrasive resistance; popular balance of cost and longevity.
• Molded Polymer (Plastic): Resistant to chemical corrosion, but susceptible to mechanical damage if cleaned with hard objects. Moderate wear life when spraying liquid solutions.
• Brass: Extremely soft metal that wears rapidly when spraying abrasive suspensions (WP, DF, F). As brass orifices erode, nozzle output increases significantly (leading to over-application, crop injury, and legal violations) and spray pattern distorts. Brass nozzles should never be used with abrasive formulations.

Cleaning Note: Applicators must NEVER use metal pins, wire, or pocket knives to clean clogged nozzles, as hard tools permanently alter orifice geometry. Always use a soft-bristled brush or compressed air.

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Nozzle Spray Patterns & Applications

  Standard Flat Fan           Even Flat Fan (E)            Hollow Cone
 (Tapered Edges - Overlap)   (Uniform Band - NO Overlap)   (Circular - Canopy Penetration)
    /   |   \                     |   |   |                     /  (   )  \
   /____|____\                    |___|___|                    /___(___)___\

1. Standard Flat Fan Nozzles

• Pattern Description: Produces a flat sheet of spray with tapered edges. Center output is higher than edge output.
• Application: Designed for broadcast application on spray booms. Booms must be adjusted to proper height so that adjacent nozzle spray patterns overlap by 30% to 50%, ensuring uniform deposit across the field.
• Fan Angles: Standard angles are 65°, 80°, and 110°. Wider fan angles (110°) allow lower boom heights, reducing wind drift exposure.

2. Even Flat Fan Nozzles (Designated by 'E')

• Pattern Description: Delivers an even, uniform volume distribution across the entire pattern width, with sharp outer cut-offs.
• Application: Designed exclusively for band spraying over crop rows or targeted strip applications. NEVER overlapped on a spray boom.

3. Cone Nozzles (Hollow Cone & Solid Cone)

• Hollow Cone: Delivers spray in a circular ring with no droplets in the center. Produces fine droplet sizes that swirl into dense plant canopies, providing thorough coverage for insecticides and fungicides.
• Solid Cone: Produces a circular pattern completely filled with droplets. Delivers larger droplets at higher operating pressures for foliage penetration.

4. Flood Nozzles

• Pattern Description: Wide-angle (110° to 160°) flat spray produced by deflecting a low-pressure stream off a curved surface.
• Application: Operates at low pressures (8 to 25 PSI) to produce large, drift-resistant droplets. Used for high-volume liquid fertilizer and herbicide applications.

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Chemigation Safety & WSDA Backflow Regulations

Chemigation is defined under Washington State law (RCW 17.21 and WAC 16-228) as any process whereby pesticides, fertilizers, or chemicals are applied to land or crops through an irrigation system (such as center pivots, wheel lines, drip irrigation, or micro-sprinklers).

Because chemigation systems connect directly to groundwater wells, rivers, or irrigation canals, failure of safety equipment can cause massive back-siphonage of toxic chemicals into public or private water sources.

+---------------------------------------------------------------------------------------+
|                   WSDA MANDATORY CHEMIGATION BACKFLOW ASSEMBLY                        |
|                                                                                       |
|  [Water Well] ---> (Vacuum Relief) ---> [Main Check Valve] ---> (Low Pressure Drain)  |
|                                                                          |            |
|  [Chemical Tank] -> [Injection Pump (Interlocked)] ----------------------+            |
|                                                                          v            |
|                                                                 [Irrigation Field]    |
+---------------------------------------------------------------------------------------+

WSDA Mandatory Anti-Backflow Safety Assemblies

Under WAC 16-228-1320, no pesticide may be injected into an irrigation system unless the system is equipped with the following functional safety devices:

1. Main Line Check Valve: A positive-closing, spring-loaded check valve located in the main irrigation pipeline upstream of the chemical injection point. Prevents reverse flow of water-chemical mixtures back into the water supply source.
2. Vacuum Relief Valve: Installed on top of the main irrigation pipe between the check valve and the water source. Opens automatically to admit air when water flow stops, breaking any siphon vacuum.
3. Automatic Low-Pressure Drain: Positioned on the underside of the main pipeline between the check valve and the water source. Automatically opens to discharge any liquid leakage away from the water source if the main check valve fails to seal completely.
4. Interlocked Power Supply: An electrical or mechanical control interlock that connects the chemical injection pump power supply directly to the main irrigation pump power supply. If the irrigation pump stops or water pressure fails, the injection pump automatically shuts down immediately, preventing raw pesticide from being pumped into stagnant lines or overflowing onto the soil.
5. In-Line Injection Hose Check Valve: A small, corrosion-resistant, spring-loaded check valve located at the injection point on the chemical line. Prevents irrigation water from flowing backward through the injection hose into the pesticide supply tank.