This article was co-developed with Mark Ledebuhr of Application Insight, LLC.
Fluid Handling Systems
How is an airblast sprayer different from any other agricultural sprayer? Fundamentally, airblast sprayers are used in horticulture to convey spray to a target using directed air. They employ two interrelated fluid handling systems: A pneumatic system (air handling) and a hydraulic system (liquid handling).
The operator’s ability to control these systems independent of one another is a function of sprayer design, and the design is highly variable. This is one of the reasons it’s so difficult to develop a universal protocol for optimizing the configuration of an airblast sprayer; best practices can sometimes conflict as a function of sprayer design.
Recognizing this, we’ve categorized common designs according to their air- and fluid-handling systems. Using these categories, stakeholders can refer to them specifically when a sprayer design requires special consideration. Each air handling category features a corresponding silhouette.
These generic images are intended to give clarity, and not to advocate any brand or design variation.
Air Handling Categories
Air is generated by some form of fan (e.g. radial, tangential, squirrel-cage, turbine). A single sprayer can feature single or multiple fans that are in-line, stacked or distributed around the target canopy. Air direction can be adjusted to some degree as it is channelled or deflected from single or multiple sources.
Low Profile Radial (LPR)
Perhaps the most recognizable design, the LPR permits limited adjustment to air direction using deflectors or moveable outlets. Air is generated by radial fan(s) or turbine and the net movement is directed laterally / upward.
Fixed Vertical Tower (FVT)
The FVT permits limited adjustment to air direction using deflectors or moveable outlets. Air is channelled by tubes, bags or duct(s) and the net movement is directed laterally.
The CN permits extensive adjustment to air direction using deflectors and a vertical duct with a positional outlet. Point-source air can be channelled in any direction, but only to one side at a time.
Targeted Tower (TT)
The TT permits moderate adjustment to air direction using deflectors, moveable outlets or fan orientation. Air can be channelled by tubes, bags or ducts or by orienting multiple fans on an adjustable mast. Air outlets are equidistant from the canopy profile, positioned on one side and possibly above. The net movement of air is lateral / downward.
Wrap-Around / Multirow (WAM)
The WAM permits moderate adjustment to air direction using deflectors, moveable outlets or fan orientation. Air can be channelled by tubes, bags or ducts or by orienting multiple fans on an adjustable mast. Air outlets are equidistant from the canopy profile, positioned on both sides and possibly above. The net movement of air is neutral / downward.
Liquid Handling Categories
Liquid is moved by a positive displacement (e.g. piston diaphragm, peristaltic) or centrifugal pump through a manifold terminating in some form of atomizer that converts the liquid to spray droplets. The liquid flow rate and spray quality may or may not be independent of the air handling.
Nozzles employ a combination of pressure and flow-based metering. Spray shape, droplet size and flow rate are independent of air handling. The position of the nozzle body relative to the air outlet affects spray quality. These systems produce a moderate range of flow and a wide range of droplet sizes.
Air shear employs flow-based metering. These systems produce a wide wide range of flow rates, but droplet size is finer and dependant on air handling.
Atomizers employ flow-based metering. These systems have the widest range of flow rates, but droplet size is finer and dependant on air handling.
Pneumatic systems employ pressure-based metering. These systems have a narrow range of flow rates, require high pressure and are dependant on air handling. They produce the finest droplet sizes.
In adopting this system of classification, we believe the process of optimizing sprayer configuration and calibration can be made less complicated. A universal language facilitates clear communication between growers, industry and consultants/specialists.
With certain exceptions, there are commercial examples of airblast sprayers that feature every combination of air and liquid handling described here. We acknowledge that there may be rare sprayers that don’t fit these categories… but let’s keep things simple.