Array of designer nozzles provides options, creates confusion
It's not like the old days when a couple of flat fan nozzles were the only ones you needed in the tool box.
Posted: May 26, 2005
It's a jungle out there. Sorting out which sprayer nozzle to use for which spraying operation can be a confusing decision these days, with nearly a dozen nozzle manufacturers and a wide range of capacities and models on the market.
Along with the standard nozzles are extended range models, pre-orifice, combo jets, and air induction nozzles, as well as the option of low drift, and high and low pressure models within each type.
The fact is, no single system works best for all situations, says Brian Storozynsky, a sprayer technology specialist with Alberta's AgTech Centre in Lethbridge. Everything has a fit, depending on needs. Nozzle selection can be influenced by the pressure capability of the sprayer, the water volume to be used, preferred travel speed, drift tolerance, and the type of pesticide being used - not only whether it is a herbicide or a fungicide, but whether it's a broadleaf or grassy weed herbicide.
One of the newer trends in nozzle design catching producer interest across the country is the air induction or venturi nozzle, says Storozynsky. A main feature of the venturi nozzle is that it produces a coarser droplet size, which is important to producers looking to manage spray drift.
With the air induction venturi nozzles, the spray solution flows through a tapered passage in the centre of the nozzle; it draws in air, which mixes with the liquid, trapping air bubbles inside the spray solution droplets.
Venturi nozzles actually have two orifices. The first meters the flow of the chemical and faces the most pressure. The second orifice creates the spray pattern and is usually twice as large as the metering orifice. For example, with a 02 metering orifice, the pattern orifice would be at least a 04.
The diagram shows how venturi nozzles work. The spray solution passes through a tapered passage (A) in the nozzle. As the passage diameter decreases, the spray is accelerated through. At the tapered passage outlet (B), a vacuum is created causing air to be sucked from outside the nozzle tip through one or two holes (C). The spray solution and air are mixed in chamber (D) before exiting the nozzle tip (E). The compression in the mixing chamber results in air bubbles forming inside the liquid spray droplets. This produces larger spray droplets that, according to some nozzle manufacturers and distributors, have a positive affect. Spray drift can be reduced significantly without sacrificing spray coverage and chemical efficacy. It should be noted that the internal orifice regulates flow and the external tip shapes the spray.
Air venturi nozzles
Since the pattern orifice is larger than the metering orifice, there is a significant pressure drop between the two as air is drawn in through the venturi and mixed with the spray. As a result, the venturi-style tips produce larger spray droplets and fewer driftable fines than equivalent-size conventional nozzles at the same pressure, says Storozynsky.
Depending on the manufacturer and size, venturi nozzles are divided into low pressure and high pressure nozzle categories.
Good weed control
Coarser droplet size doesn't mean a loss of herbicide efficacy, points out Storozynsky. Five years of research results comparing different nozzle types on both pull type and high clearance sprayers tells the story.
"In our work, we found herbicide efficacy (weed control) with venturi nozzles was equal to other nozzle types with the added benefit of reduced drift," he said. (See: AgTech Innovator)
Storozynsky found the air-induction nozzles provided as effective weed control as other nozzle types, most years. "It has long been viewed that a finer droplet size provided better coverage and therefore improved herbicide efficacy," says Storozynsky. "But, four out of five years, research showed venturi nozzles were just as effective as nozzles producing a finer spray."
The exception was reduced weed control in plots with a dense population of grassy weeds, and especially at reduced herbicide rates.
Agriculture and Agri-Food Canada researcher, Dr. Tom Wolf has similar findings from his research.
Keep droplet numbers up
"Coarser droplets can reduce coverage, but it's not important at reasonable water volumes," says Wolf. "In most cases, coverage is similar and efficacy is the same for broadleaf herbicides and fungicides at the 10 gallon per acre rate. Grassy herbicides require some caution. Don't use a combination of very coarse sprays and low carrier volumes, and do maintain high pressures."
Wolf's research shows droplet number per square inch is more important than droplet size for determining efficacy. Pressure and volume should be adjusted to maintain at least 300 to 500 drops per square inch on water-sensitive paper, or 10 to 15 percent coverage.
Larger and more uniform droplets imply better coverage and the possibility of reducing water volumes, but Wolf advises producers to be cautious. (Link to Wolf's reports on the Nozzle Market)
"Low drift nozzles are designed to reduce drift, and they do this by eliminating many of the finer droplets and adding some larger ones," explains Wolf. "A low-drift spray reduces the number of droplets available for coverage, even if they are 'more uniform.'
"In practice, this is offset by reduced water volumes and the need to use finer sprays to keep droplet numbers up. But you can compromise. Use a reasonable water volume (five to seven gallons per acre) and an intermediate low-drift nozzle, such as a low-pressure air induced."
Adoption of new nozzle designs is a learning process for producers, points out Helmut Spieser, an engineer and pesticide application specialist with the Ontario Ministry of Agriculture and Food in Ridgetown.
"Probably about half our producers use some type of air induction nozzle, but it's been a slow growth," he says. "The early adopters were quick to use the technology, but now, with a choice of 20 or more models, it's a difficult decision. A lot depends on the year, too. If windy conditions delay spraying, then we see more farmers interested in nozzles that reduce drift."
The new design also means farmers need to adjust sprayer settings. "For years we did too good a job telling people that running sprayers at 40 psi was adequate," adds Spieser. "Now, with the venturi nozzle, if the boom pressure is 40 psi, the pressure at the nozzle tip is much less. Farmers need to learn if they want 40 psi at the tip, they have to increase boom pressure to perhaps 80 psi."
Spieser says more producers are running sprayers with two types of nozzles, both the same size. "One nozzle is a flat fan type and the other is a venturi," he says. "Depending on conditions, they'll use the air induction to manage drift and the flat fan for coverage. They interchange the nozzles as field conditions change."