How Long Do Spray Nozzles Last?
Worn spray nozzles can have a significant impact on the performance of your sprayer and ultimately the crop protection chemistry it is used to apply. In the graphic below we have calculated the effect on pressure and droplet size resulting from the use of nozzles exhibiting 10% wear. Modern sprayers utilize flow rate controllers to maintain a desired application volume. To do this the flow rate controller monitors the liquid flow rate out of the boom and matches it with the ground speed of the sprayer to maintain your desired application volume. As nozzles wear the orifices increase in size and allow for more liquid volume to pass through them. When using worn spray nozzles, the flow rate controller will compensate for the increase in flow rate by reducing spray system pressure.
Reducing spray system pressure can have a resulting impact on spray nozzle performance by influencing droplet size, coverage and spray pattern distribution. When spraying at lower pressures worn spray nozzles can result in pressure reductions below the minimum pressure for a given nozzle. We can also experience changes in droplet size resulting from pressure reductions in worn spray nozzles (Table1). These increases in droplet size can have a negative impact on spray coverage. If the pressure reduction is significant it is possible to see reductions in spray angle, also known as pattern collapse that can negatively impact spray coverage and application distribution across your fields.
But how do you know when spray nozzles are worn and should be changed? How can you avoid the performance issues related to worn spray nozzles? And how long should we expect spray nozzles to last?
Flow rate in gallons per minute (GPM) at 40 psi is used to measure the % wear of a spray nozzle. By collecting the flow through nozzles at 40 psi, we can determine the level of nozzle wear by comparing the captured volume versus the manufacture stated flow volume for that spray nozzle. The application industry recommends changing nozzles when they reach 10% wear, or an increase in flow rate of 10% greater than the manufacture stated flow rate.
To answer the question of how long spray nozzles last, Pentair Hypro supplied 3D nozzles to applicators in order to produce field wear and tear. For one spraying season these nozzles were used to apply herbicides and fungicides to 8, 10, 27, 30, 38, 40 and 44,000 acres to produce nozzle sets with varying degrees of wear.
Nozzles were then retrieved and their respective flow rates were collected using a bench top spray table with pressure set to 40 psi. A handheld Spot On calibrator was used to collect and measure flow rate. Flow rates in gallons per minute were recorded and used to calculate % wear by number of acres sprayed.
Nozzles used to apply 8,000 acres of crop protection chemistry showed no signs of wear present. Significant signs of nozzle wear were not detected until nozzles had applied 30,000 acres of crop protection chemistry, when 5% wear was recorded. The 10% wear threshold was crossed with nozzles that applied 40,000 acres. Nozzles seeing 40,000 acres of use exhibited a 12% increase in flow rate compared to a 3D100-04 nozzle that is new (Figure1).
Coefficient of Variation (CV) is a metric used to quantify the uniformity of a spray pattern. A higher percent CV number indicates lower uniformity of spray droplet distribution. Areas under a spray boom will receive a higher dose, while other areas will receive a lower dose. Similar to golf, a lower percent CV number is the goal. For agricultural spray nozzles the accepted threshold to remain under is 7%.
The same spray nozzles that were used for the flow rate and wear testing were also tested to determine their uniformity of spray pattern distribution. Nozzles used on 44,000 acres exhibited an 80% increase in the spray pattern CV compared to the same nozzle when new. When new Pentair Hypro 3D-04 nozzles displayed a CV of 3.1% at 40 psi, however, after 40,000 acres of use these same nozzles displayed a CV of 7.5% at 40 psi. This CV after 40,000 acres of usage crosses over the desired threshold of 7% CV for agricultural spray nozzles. Increasing levels of CV will reduce the accuracy and precision of an application and may have potential if left unchecked to allow pest control escapes to occur.
From this field and lab testing we have determined that 40,000 should be used as an expected lifespan for agricultural spray nozzles made of polyacetal. Once you reach 40,000 acres of use it is recommended to check spray nozzles for wear and condition. Check at 5,000 acre intervals until flow rate increases to 10% above manufacturer stated flow rate at 40 psi.
Fall/early winter will be the best time to check your sprayer for worn or damaged nozzles. This will give you the winter months to acquire new nozzles if needed. With all the supply chain disruptions and higher than usual demand we have seen this year, I could foresee some backorder issues in the spring when demand for new nozzles and other sprayer parts is highest. Checking the condition of your nozzles this fall will help you get parts orders in early so your sprayer is in prime condition when the spring spraying season arrives.
Article contributed by Nick Fleitz, Agronomist at Pentair-Hypro