Application Equipment Types, Pumps, Agitation, and Tank Components
Key Takeaways
- Roller pumps handle non-abrasive liquid formulations up to 50–300 PSI but experience rapid roller wear when pumping abrasive wettable powders (WP) or dry flowables (DF).
- Centrifugal pumps deliver high volumetric flow (up to 70–130 GPM) at low-to-moderate operating pressures (up to 70 PSI) and require high rotational speeds (3,000–4,500 RPM).
- Hydraulic agitation requires dedicated high-volume pump bypass (at least 20–30% of total pump output capacity) to keep wettable powders continuously suspended in the tank.
- Positive displacement diaphragm and piston pumps provide high operating pressures (piston up to 1,000+ PSI; diaphragm up to 700+ PSI) suitable for abrasive suspensions and high-pressure orchard spraying.
- Spray system strainers are rated by mesh count, utilizing coarser strainers (25–50 mesh) on suction lines to protect the pump and finer strainers (50–100 mesh) at nozzle tips to prevent clogging.
Application Equipment Types, Pumps, Agitation, and Tank Components
Quick Answer: Selecting the correct pesticide application equipment depends on the target site, formulation type, required operating pressure, and flow rate. Positive displacement pumps (piston, diaphragm, roller) deliver fluid output proportional to speed, whereas non-positive displacement pumps (centrifugal) rely on impeller speed and discharge pressure. Suspensions such as wettable powders (WP) require vigorous continuous agitation—either mechanical paddles or high-volume hydraulic bypass—to prevent settling.
Pesticide application equipment must convert liquid or granular formulations into uniform droplets or particles and deliver them accurately to the target site. Florida applicator certification exams test your knowledge of sprayer types, pump operating principles, formulation compatibility, tank agitation mechanics, and filtration systems.
Overview of Application Equipment Categories
Application machinery is classified by the carrier medium (liquid vs. granular) and the method used to convey pesticide to the target canopy or soil surface.
1. Hydraulic Boom Sprayers
Hydraulic sprayers use liquid pressure generated by a pump to atomize the spray mixture through nozzle orifices. Tractor-mounted, self-propelled, or towed boom sprayers apply herbicides, fungicides, and insecticides to field crops, turfgrass, and rights-of-way. Operating pressures typically range from 20 to 60 PSI.
2. Air-Assisted (Air-Blast) Sprayers
Air-blast sprayers use liquid pressure to deliver spray to nozzles situated in a high-velocity airstream generated by an engine-driven fan. The airstream carries droplets into dense tree canopies in citrus groves, orchards, and vineyards. They handle low-to-high volumes (50 to 400+ GPA) at pressures of 80 to 260+ PSI.
3. Handheld and Backpack Sprayers
Small-capacity sprayers (1 to 5 gallons) rely on manual lever pumping or compressed air/electric pumps. Operating at 15 to 45 PSI, they are used for spot applications, perimeter barrier sprays, structural pest control, and ornamental turf maintenance.
4. Granular Applicators
Granular spreaders apply dry, ready-to-use granules (G) or pellets (P). Drop spreaders release granules through a bottom gate directly beneath the hopper, providing crisp swath edges with zero drift risk. Rotary (centrifugal) spreaders drop granules onto a spinning disk, throwing particles over a wide swath (8 to 30 feet).
Spray Pump Selection & Operational Mechanics
The pump is the heart of the hydraulic spraying system. Pumps are divided into two main engineering classes: positive displacement and non-positive displacement.
| Pump Type | Displacement Class | Pressure Range (PSI) | Max Flow (GPM) | Abrasive Tolerance (WP/DF) | Key Characteristics & Best Uses |
|---|---|---|---|---|---|
| Roller | Positive | 50 – 300 PSI | 8 – 30 GPM | Low | Nylon or Teflon rollers inside cast iron/poly housing; economical; ruined quickly by abrasive powders; ideal for soluble liquids and emulsifiable concentrates (EC). |
| Centrifugal | Non-Positive | 5 – 70 PSI | 70 – 130+ GPM | High | High volume, low pressure; requires high RPM (3,000–4,500); handles abrasive WPs easily; non-priming; output drops if pressure increases. |
| Diaphragm | Positive | 50 – 700+ PSI | 5 – 60 GPM | Very High | Flexible synthetic diaphragms isolate oil/crankcase from spray liquid; handles harsh chemicals, abrasives, and high pressures; excellent for air-blast orchard spraying. |
| Piston | Positive | 100 – 1,000+ PSI | 2 – 35 GPM | High | Mechanical pistons deliver exact flow proportional to RPM; extremely durable; capable of intense operating pressures; used for high-tree spraying and pressure cleaning. |
Exam Tip: If a question asks which pump is best for applying a high-volume, highly abrasive wettable powder formulation at moderate pressure, choose a centrifugal pump. If high pressure (above 200 PSI) is required for dense tree spraying with an abrasive material, select a diaphragm or piston pump.
Agitation Systems: Hydraulic vs. Mechanical
Proper agitation keeps active ingredients evenly suspended throughout the spray mixture. Inadequate agitation causes pesticide settling, leading to under-application at the start of a tank load and crop injury or over-application near the bottom.
┌────────────────────────────────────────────────────────┐
│ SPRAY TANK AGITATION MODES │
└───────────────────────────┬────────────────────────────┘
│
┌─────────────────────────┴─────────────────────────┐
▼ ▼
┌─────────────────────────────┐ ┌─────────────────────────────┐
│ HYDRAULIC AGITATION │ │ MECHANICAL AGITATION │
├─────────────────────────────┤ ├─────────────────────────────┤
│ • Uses pump bypass flow │ │ • Engine/PTO shaft paddles │
│ • Requires 20-30% extra GPM │ │ • High torque, flat blades │
│ • Uses jet agitator nozzles │ │ • Essential for thick WPs │
└─────────────────────────────┘ └─────────────────────────────┘
Hydraulic Agitation
Hydraulic agitation routes excess liquid from the pump discharge back into the bottom of the tank through specialized jet agitator nozzles.
- Bypass Volume Requirement: To maintain a suspension of wettable powder (WP) or dry flowable (DF) formulations, hydraulic agitation requires 20% to 30% of total pump output capacity (or 3 to 4 GPM for every 100 gallons of tank capacity).
- Venturi Jet Agitators: Venturi nozzles install at the bottom of the tank to multiply liquid movement, drawing surrounding tank solution into the high-velocity jet stream.
Mechanical Agitation
Mechanical agitation utilizes flat paddles or propeller impellers mounted on a rotating shaft near the tank bottom, driven directly by an electric motor, hydraulic motor, or power take-off (PTO) shaft.
- Power Demands: Mechanical agitation provides intense mixing power without consuming pump volumetric output capacity.
- Essential Use: Mandatory when applying dense, viscous suspensions or when operating pumps with low volumetric output.
Spray Tank Components, Materials, & Filtration
Spray Tank Construction Materials
- Polyethylene (Plastic): Lightweight, corrosion-resistant, relatively inexpensive. Disadvantage: Cannot be repaired easily if cracked; translucent walls help monitor liquid level.
- Fiberglass: Highly durable, chemically resistant, easily repaired with resin kits. Disadvantage: Opaque; requires a sight gauge tube to check liquid level.
- Stainless Steel: Premium durability, completely non-corrosive, smooth internal walls prevent chemical absorption. Disadvantage: Heavy and expensive.
- Aluminum: Lightweight; vulnerable to corrosion from acidic or strongly alkaline liquid fertilizers and pesticides.
Strainer & Filtration System Order
Filtration protects system pumps, valves, and nozzle tips from abrasive wear and clogging debris. Strainers are rated by mesh count (number of openings per linear inch). Higher mesh numbers mean smaller screen openings.
- Tank Filler Basket (16–20 Mesh): Fits in the top tank fill opening to catch large debris when filling with water.
- Suction (Inlet) Strainer (25–50 Mesh): Placed on the intake line between tank and pump inlet. Protects pump internal gears/rollers. Must be coarse enough not to restrict pump intake flow, which causes pump cavitation.
- Line (In-Line Pressure) Strainer (50–80 Mesh): Positioned on the discharge line downstream of the pump and pressure control valve. Prevents debris from reaching boom shutoff valves.
- Nozzle Tip Strainers (50–100 Mesh): Placed directly behind nozzle tips. Must have openings smaller than the nozzle orifice. Slotted strainers or 50-mesh screens are standard for high-flow tips; 100-mesh screens are required for small orifices (e.g., 0.1 to 0.15 GPM tips).
Equipment Inspection & Pre-Operation Protocol
Before entering the field, applicators must perform a 5-step pre-operation system check:
- Inspect hoses for cracks, bulges, soft spots, or leaking quick-coupler gaskets.
- Clean all inline screens and nozzle strainers using a soft brush (never use metal wire or mouth blowing).
- Fill tank half full with clean water and operate pump at working pressure to check for system leaks.
- Verify smooth operation of pressure regulator valve and agitation system.
- Catch output from each nozzle tip for 1 minute; replace any tip whose flow rate deviates by more than ±5% to ±10% from the manufacturer rating or nozzle average.
A Florida agricultural applicator plans to apply a wettable powder (WP) herbicide using a hydraulic boom sprayer with a 300-gallon tank. Which pump bypass flow volume is required for proper hydraulic agitation to keep the WP suspended?
Which spray pump type is LEAST suitable for applying abrasive wettable powder (WP) or dry flowable (DF) formulations due to rapid internal wear?
In what order should strainers be arranged from the spray tank to the nozzle tip, and how do their mesh counts compare?