Airblast Orchard Sprayer Product

Overview

The airblast orchard sprayer uses a high-velocity axial fan to disperse liquid pesticide (fungicides, insecticides, or herbicides) into dense tree canopies, achieving canopy penetration and coverage unattainable with low-pressure boom sprayers. The machine is essential for disease and pest management in fruit trees (apples, pears, stone fruits, citrus, olives) where dense foliage prevents passive settling of spray droplets on lower canopy surfaces.

Modern airblast sprayers deliver 50–400 L/hectare of liquid formulation (concentration varies by active ingredient and target pest) with mean droplet diameter of 100–150 µm—optimal for penetration and retention on foliar wax. The machine consists of a tractor-towed frame carrying a 600–1000 L pesticide tank, a standalone engine-driven axial fan, a liquid supply pump driven by tractor PTO, and a spray nozzle ring mounted on the fan shroud.

How it works

Airflow Generation: The Axial Fan Assembly is powered by a 10–15 kW gasoline or small diesel engine mounted directly on the sprayer frame. An aluminum axial fan impeller (800–1000 mm diameter, 8 blades, 0.5° pitch angle) spins at 3600 rpm, generating axial airflow of 40–60 m/s (90–130 mph) at the discharge opening. This high velocity is essential: orchard canopies are dense (leaf area index of 4–6, meaning 4–6 m² of leaves per m² ground area); airflow must penetrate 1–2 meters into the canopy to reach fruit-bearing branches and interior leaf surfaces where insects and fungal infections occur.

Fan shroud design is critical: a diffuser section just downstream of the impeller transitions the high-velocity jet into a more uniform discharge (still 40–60 m/s, but spread across a wider area). The shroud can be rotated ±45° horizontally (worm-gear slew mechanism) to direct the airstream toward adjacent tree rows, and tilted vertically (hydraulic or manual adjuster) to direct airflow upward into canopy peaks, sideways into middle canopy, or downward toward base and trunk.

Liquid Supply and Atomization: Pesticide solution is pumped from the Liquid System by a 25 cc/rev gear pump (50 L/min capacity) driven from the tractor's 540 rpm PTO shaft via a gear reducer or belt drive. Pressure is maintained at 40–50 psi by a relief valve; actual operating pressure is typically 35–45 psi. Liquid is metered through a needle valve or proportional directional valve (modulated by the operator from the tractor cab) to the spray nozzle ring.

Six hollow-cone or fan-spray nozzles (0.5–1.5 GPM each, collectively 3–9 GPM) are positioned on the fan shroud at radial spacing matching the fan discharge pattern. As pressurized liquid emerges from each nozzle, it atomizes into fine droplets entrained in the airstream. Nozzle capacity determines spray rate: a 3 GPM system at 0.75 hectares per hour forward speed delivers approximately 400 L/hectare; a 9 GPM system delivers 1200 L/hectare. Operators select nozzle size (marked 00–06, corresponding to orifice diameter) based on target flow rate and field capacity.

Droplet Deposition: High-velocity airflow carries droplets deep into canopy, impacting leaves on upper, middle, and lower canopy strata. Droplet size distribution (100–150 µm mean diameter) is optimized for canopy retention: droplets >200 µm fall quickly through foliage without reaching lower canopy; droplets <50 µm drift and are lost to air currents. The axial fan design (parallel discharge, minimal swirl) reduces drift compared to tangential or centrifugal fans, important for environmental compliance and neighboring-field spray drift avoidance.

Tank and Circulation: The Liquid System holds 600–1000 L of diluted pesticide mixture. A suction-line strainer (200 mesh) at the tank bottom prevents large particles from reaching the pump. A return-line filter (100 mesh, 25 L/min capacity) catches pump wear debris and undissolved formulation particles, protecting nozzles from plugging. A paddle agitator or suction-line return jet maintains mixture suspension (critical for wettable powders and microemulsions) and prevents settling during operation. An agitation bypass valve or proportional flow control allows the operator to run agitation independent of spray, useful during idle periods or refilling.

Operator Control: A simple control panel mounted on the tractor or sprayer allows the operator to: toggle spray on/off via solenoid directional valve, modulate spray rate (needle valve or proportional valve adjuster) to vary application intensity, monitor pressure (glycerin-filled gauge) and flow rate (optional magnetic meter), and adjust fan shroud angle (hydraulic or manual controls) to direct airstream. Forward speed is held constant (typically 4–6 km/h for fruit tree orchards, up to 10 km/h for vineyard application) to achieve target spray volume per hectare.

Chassis and Mobility: The towed chassis (80 mm welded steel angle-iron frame) carries wheels (11.2/50 agricultural tires, single axle typical for 600 L tank, tandem for 1000 L) on leaf spring suspension. A ball coupler drawbar attaches to the tractor three-point linkage or drawbar. Quick-disconnect hydraulic couplers on the drawbar connect tractor hydraulic power (for boom tilt) and PTO shaft couples to the pump drive. The entire assembly is 3–4 meters long and 1.5 meters wide, maneuverable in tight orchard spaces (row spacing 4–8 m).

Spray Drift Mitigation: Airblast sprayers generate more drift than low-pressure boom sprayers because high-velocity air entrains droplets and carries them beyond the immediate spray zone. Modern sprayers reduce drift via: reduced nozzle capacity (smaller droplet source), air induction nozzles (larger, air-filled droplets that are less prone to drift), fan speed reduction (slower airflow generates less drift, though penetration is reduced), and chemical adjuvants (oils, polymers, or drift-control agents that increase droplet size or adhesiveness). Regulatory restrictions in sensitive regions (apiaries, residential areas) may prohibit airblast use or mandate low-drift configurations.

Maintenance: After 40 hours of operation, inspect nozzles for wear (orifice enlargement causes higher flow and coarser spray); replace worn nozzles (cost ~$5–20 per nozzle). Check hoses and connections for seeps. Change pump oil (25 cc/rev gear pump typically uses SAE 10W-30) every 100 operating hours. At season end, flush tank and lines with clean water; allow to dry or purge with compressed air before storage to prevent corrosion.