Selecting nozzles for a conventional airblast sprayer is not a simple decision. Airblast-applied agrichemicals have become very specific with regards to target and timing and many of the crops traditionally sprayed with an airblast sprayer are being planted in higher densities. Consequently, airblast operators are increasingly concerned with improving coverage while minimizing off-target losses. To accomplish this, they recognize that multiple sets of nozzles may be required during the spray season to match the variable shape, size and density of their crops.
For example, a large apple orchard may require as many as five different nozzle combinations over a season: One set for dilute applications like a dormant oil drench, two sets for high-density blocks (one for spring and one for after petal fall), and two sets for semi-dwarf blocks (one for spring and one for after petal fall). This means the operator should be choosing nozzles that give a specific spray quality.
Hollow cone spray patterns are the most common choice for airblast sprayers, but full cone or even flat fans are occasionally used. Typically, disc & core (aka disc & whirl) combination nozzles are used to produce the hollow and full cone patterns. Some require spacers and washers and some do not. They are available in many materials and diameters, ranging from hard ceramic to soft brass.
The rate of tip wear depends on sprayer pressure, product sprayed, and the material the nozzle is made of. Upgrading to a harder, more durable tip can reduce maintenance costs, but costs more initially. I suggest that brass tips should not be used for day-to-day operation, but they are ideal for calibration. Owning a library of brass discs & cores will allow you to experiment to find the best nozzle configuration for your sprayer. Once you’ve determined the best rate for each nozzle position, you can purchase the equivalent nozzles in the more expensive ceramic disc & core.
Inevitably, all nozzles wear out – even ceramic. At minimum, replace softer materials biannually, or when two nozzles are emitting 10% (or preferably, 5%) more than the manufacturer’s rated output. This will save money in over spray and/or reduced coverage from a degrading spray quality.
Many growers say their tanks empty in the same place every time, so their nozzles aren’t worn. This is only half the issue. Nozzles can be distorted, compromising spray quality, and still produce an acceptable rate. A distorted spray quality can have a negative effect on spray coverage.