11.1 Types of Application Equipment & Component Selection
Key Takeaways
- Hydraulic sprayers use liquid under pressure to atomize spray mixtures, ranging from low-pressure hand-held and backpack sprayers for localized treatments to high-pressure tractor-mounted boom sprayers for field crops and turf.
- Air-blast sprayers utilize fan-driven high-velocity airflow to carry finely atomized spray droplets deep into dense tree canopies and orchard foliage, requiring careful calibration to minimize drift.
- Granular applicators fall into two main categories: drop spreaders, which deliver precise, sharp-bordered applications directly beneath the hopper, and rotary (centrifugal) spreaders, which cover wider swaths with feathered edges but are sensitive to wind and particle size.
- Selecting the proper sprayer pump requires matching operational requirements: roller pumps offer low cost at moderate pressure (50–300 PSI) but wear quickly with abrasive wettable powders; centrifugal pumps handle abrasive slurries at high flow rates (up to 130 GPM) at low pressure (<70 PSI); diaphragm pumps withstand corrosive and abrasive chemicals at high pressure; and piston pumps provide high pressure (up to 1,000 PSI) for tree spraying.
- Sprayer filtration relies on a sequential strainer system where mesh sizes increase as flow proceeds toward the nozzle (tank basket 16–30 mesh, suction strainer 50 mesh, in-line filter 50–80 mesh, nozzle screen 50–100 mesh), preventing nozzle clogging and pump damage.
11.1 Types of Application Equipment & Component Selection
Pesticide application equipment ranges from small, hand-operated devices to large, self-propelled, computer-controlled field sprayers and granular spreaders. Selecting the correct equipment type and component configuration is critical for delivering the exact labeled rate of pesticide to the target site while minimizing off-target movement, worker exposure, and equipment degradation.
Hydraulic Sprayers
Hydraulic sprayers use liquid pressure generated by a pump to atomize liquid spray mixtures into droplets and propel them toward the target. They are the most common equipment type used in agricultural, rights-of-way, turf, and ornamental pest management.
Handheld & Backpack Sprayers
Handheld compressed-air sprayers and manual or battery-powered backpack sprayers are designed for small-scale, spot, or precision applications.
- Compressed-Air Sprayers: Operate by pumping air into a sealed tank above the liquid formulation. Operating pressure starts high (40–50 PSI) and gradually decreases as liquid is discharged, which alters flow rate and droplet size unless equipped with a constant-pressure control valve.
- Backpack Sprayers: Feature a lever-operated diaphragm or piston pump maintained by the operator while spraying, or a battery-powered electric pump, providing continuous pressure (typically 20–60 PSI). They are widely used for spot treatments in turf, nursery container beds, brush control, and structural perimeters.
Low-Pressure Boom Sprayers
Low-pressure hydraulic sprayers operate at pressures between 15 and 60 PSI and are mounted on tractors, trailers, or utility vehicles.
- Application Scope: Designed primarily for broadcast applications of herbicides, insecticides, and liquid fertilizers over field crops, pastures, and turfgrass.
- Boom Design: Consists of a horizontal pipe or truss holding a series of evenly spaced nozzles. Low pressure reduces fine droplet production, helping minimize off-target spray drift.
High-Pressure Hydraulic Sprayers
High-pressure sprayers operate at pressures ranging from 150 to over 1,000 PSI, utilizing heavy-duty piston pumps.
- Application Scope: Used to spray tall shade trees, dense brush, and livestock, or for high-volume foliar fungicide penetration in dense canopies.
- Characteristics: High pressure creates fine droplets and high velocity, allowing spray streams to reach heights of 30 feet or more, but drastically increases off-target drift risks if wind is present.
Air-Blast Sprayers
Air-blast (or air-assisted) sprayers use a combination of hydraulic pressure and high-velocity air streams to carry pesticide droplets into target foliage.
| Component / Parameter | Operational Function & Specifications |
|---|---|
| Hydraulic Nozzles | Atomize liquid under moderate pressure (60–200 PSI) into a fine droplet mist directly in front of an air outlet. |
| Axial or Radial Fan | Generates air volumes from 5,000 to over 40,000 cubic feet per minute (CFM) at air speeds of 80 to 150 MPH. |
| Foliar Displacement | High-velocity air displaces calm ambient air within tree canopies, moving leaves to expose both upper and lower leaf surfaces. |
| Primary Uses | Orchards (apples, peaches, citrus), vineyards, pecan groves, and large shade trees. |
| Drift & Environmental Risk | High potential for upward and downwind spray drift; requires turning off outer nozzles at row ends and avoiding applications during high winds or inversions. |
Granular Applicators
Granular applicators apply dry, ready-to-use formulation particles (granules or pellets) without mixing with water. They are widely used for soil insecticides, pre-emergence herbicides, fungicides, and fertilizers.
Drop Spreaders (Gravity-Feed)
Drop spreaders feature a hopper with a row of adjustable discharge openings at the bottom. A rotating agitator bar pushes granules through the openings, dropping them directly onto the ground by gravity.
- Precision & Edge Control: The application swath width is exactly equal to the length of the hopper box. Drop spreaders create a sharp, distinct boundary edge with zero overthrow.
- Best Applications: Ideal for precise applications near sidewalk edges, ornamental beds, water features, and small residential lawns where off-target deposition onto hardscapes must be avoided.
- Limitations: Narrow application swath (typically 2 to 4 feet) requires more passes; wheel overlaps must be exact to prevent skippers or double-dosing.
Rotary Spreaders (Centrifugal)
Rotary spreaders drop granules onto a spinning flat disk or impellers that throw particles outward in a wide circular arc.
- Swath Characteristics: Cover a wide application swath (typically 8 to 24 feet), allowing rapid treatment of large turf areas, sports fields, and pastures. The application pattern tapers at the outer edges, requiring a 30% to 50% pass-to-pass overlap.
- Limitations: Granules are thrown into the air, making distribution highly susceptible to wind shear. Heavy particles throw farther than light particles (particle segregation), and off-target overthrow onto driveways or non-target beds is common if edge guards are not utilized.
Foggers & Soil Fumigation Equipment
Foggers & Aerosol Generators
- Thermal Foggers: Vaporize liquid pesticide formulations by injecting them into a high-temperature exhaust gas stream, producing dense smoke-like fogs with droplet sizes under 10 micrometers ($\mu m$). Used for adult mosquito control and greenhouse pest knockdowns.
- Cold Foggers / ULV (Ultra-Low Volume): Use mechanical shear from high-speed turbine air to produce fine aerosols (10–30 $\mu m$) without heat, preserving active ingredient integrity in public health and vector control operations.
Soil Fumigation Equipment
Soil fumigants are volatile liquids or gases injected directly into soil to control nematodes, soil-borne fungi, and weed seeds.
- Injection Rigs: Heavy tractor-drawn rigs equipped with rigid chisel shanks hold liquid delivery tubes that inject fumigants 6 to 18 inches below the soil surface.
- Sealing Mechanisms: Immediately following injection, the soil must be sealed using rear-mounted press wheels, ring rollers, or impermeable plastic tarps (gas-tight polyethylene or VIF/TIF films) to prevent lethal toxic fumes from escaping into the atmosphere.
Sprayer Component Selection & Engineering
[Tank & Sump] ---> [Basket Strainer 16-30 Mesh] ---> [Suction Strainer 50 Mesh] ---> [Pump (Roller/Diaphragm/Centrifugal/Piston)] ---> [Pressure Regulator & Bypass] ---> [In-Line Filter 50-80 Mesh] ---> [Boom & Nozzle Strainers 50-100 Mesh]
Sprayer Tanks
Tank material selection affects equipment longevity, chemical compatibility, and maintenance ease:
- Polyethylene: Lightweight, highly resistant to chemical corrosion, translucent for viewing liquid levels. Susceptible to ultraviolet (UV) degradation unless treated with UV inhibitors; difficult to repair if cracked.
- Fiberglass: Strong, durable, resistant to most chemicals. Translucent sight windows can be incorporated; easily repaired with fiberglass resin.
- Stainless Steel: Extremely durable, highly resistant to all agricultural chemicals and solvents, smooth interior prevents residue buildup. Heavy and costly.
- Aluminum: Lightweight, but corroded by acidic chemicals, liquid nitrogen fertilizers, and certain copper-based fungicides.
Tank design must feature a rounded bottom with a dedicated sump to ensure complete pump priming and full tank drainage, a large top fill opening equipped with a removable 16–30 mesh basket strainer, and high-volume mechanical or hydraulic agitation ports.
Sprayer Pumps
The pump is the heart of the hydraulic sprayer. Selecting the appropriate pump depends on required operating pressure, total flow volume (GPM), and chemical formulation abrasiveness.
| Pump Type | Pressure Range | Flow Volume | Formulation Compatibility | Key Strengths & Weaknesses |
|---|---|---|---|---|
| Roller Pump | 50–300 PSI | 10–30 GPM | Emulsions, soluble liquids; Poor for abrasive WP | Inexpensive, compact, self-priming; rollers and housing wear rapidly from abrasive wettable powders. |
| Diaphragm Pump | 100–850 PSI | 10–60 GPM | Excellent for all formulations including abrasive WPs | Synthetic diaphragms isolate moving parts from chemical liquid; self-priming, highly durable, handles corrosive and abrasive chemicals. |
| Centrifugal Pump | 5–70 PSI | 10–130+ GPM | Excellent for abrasive WP, DF, and liquid slurries | High volume for jet agitation; non-self-priming; impellers handle abrasive particles with minimal wear; high operating shaft RPM (3,000–4,500 RPM). |
| Piston Pump | 200–1,000+ PSI | 5–25 GPM | Good for liquid formulations; moderate for WPs | Positive displacement, high pressure capability for tree spraying; long service life with replaceable cylinder liners; expensive. |
Filtration & Strainer Sequence
System strainers prevent pump damage, valve failure, and nozzle orifice clogging. Mesh size represents the number of openings per linear inch; higher mesh numbers indicate smaller opening sizes.
- Tank Fill Basket Strainer (16–30 Mesh): Catches large debris, leaves, and undissolved chemical bags during tank filling.
- Suction Strainer (50 Mesh): Positioned between the tank outlet and pump inlet. Protects pump impellers and rollers from suspended grit. Must never be finer than 50 mesh to prevent starving the pump inlet (cavitation).
- Pressure Line / In-Line Filter (50–80 Mesh): Located downstream of the pump before control valves to protect pressure regulators and solenoid valves.
- Nozzle Screen / Strainer (50–100 Mesh): Located inside individual nozzle bodies directly behind nozzle tips. For fine nozzles spraying liquid solutions, 100 mesh screens prevent tip clogging. For heavy wettable powders or suspension concentrates, 50 mesh screens prevent clogging of the screen itself.
Pressure Regulators & Agitation Systems
- Pressure Regulator: Bypasses excess flow back to the tank to maintain constant pressure across the spray boom regardless of tractor speed changes.
- Hydraulic Agitation: Diverts a portion of pump output through jet agitators mounted in the tank bottom. Requires 5 to 6 GPM of pump capacity for every 100 gallons of tank volume to keep suspensions uniform.
- Mechanical Agitation: Uses engine-driven paddles or propellers on a shaft running through the tank bottom. Essential for heavy wettable powders and dense suspension flowables where hydraulic flow is insufficient.
Which sprayer pump type is best suited for pumping abrasive wettable powder (WP) suspensions at high flow rates and low pressure without experiencing rapid mechanical wear?
When applying granular pesticides directly adjacent to sensitive waterways or ornamental garden borders where precise placement without off-target overthrow is critical, which granular applicator should be chosen?
How does strainer mesh number relate to opening size, and which strainer screen should be positioned directly inside individual nozzle bodies when spraying liquid flowables?
A 300-gallon hydraulic sprayer utilizing a jet hydraulic agitation system requires how much pump bypass capacity dedicated solely to maintaining a uniform chemical suspension?