Constant-Rate Testing
The relationship between speed, pressure, flow rate, and spray width was observed for both boom and boomless nozzles during testing. These tests showed the typical range of the constant-rate sprayer and the effect of ATV speed changes on nozzle spray patterns, droplet size, and application rates. More extensive testing could be done to look at other speed ranges, application rates, and boom or boomless configurations.
While travel speed varied from 2 to 6 miles per hour during the boom nozzle test, the flow rate varied by no more than 1.9 gallons per acre when the flow rate was set to 20 gallons per acre (table 1). At speeds of 3 to 5 miles per hour, the flow rate was a constant 20 gallons per acre.
| Speed (mi/h) | Pressure (psi) | Flow (gpa) | Spray Width (ft) |
|---|---|---|---|
| 2 | 8 | 21.9 | 9.3 |
| 3 | 18 | 20.0 | 9.3 |
| 4 | 32 | 20.0 | 9.2 |
| 5 | 49 | 20.0 | 9.2 |
| 6 | 58 | 18.2 | 9.2 |
While travel speed varied from 2 to 5 miles per hour during the test of the bloomless nozzle, the application rate varied by no more than 3 gallons per acre when the flow rate was set to 13 gallons per acre (table 2).
| Speed (mi/h) | Pressure (psi) | Flow (gpa/acre) | Spray Width (ft) |
|---|---|---|---|
| 2.0 | 13 | 13 | 16.0 |
| 3.0 | 25 | 13 | 20.5 |
| 4.0 | 38 | 13 | 22.0 |
| 4.5 | 38 | 11 | 22.0 |
| 5.0 | 38 | 10 | 22.0 |
During tests of both the boom and boomless nozzles, the pressure required to maintain a constant flow at 2 miles per hour was less than the manufacturers' recommendations, but it was still enough to produce a reasonable spray pattern. A conventional sprayer with constant pressure calibrated at 4 miles per hour could have had a flow rate closer to 30 gallons per acre at 2 miles per hour and 12 gallons per acre at 5 miles per hour.
Test results show that the pressure to the boomless nozzle peaks at 38 pounds per square inch, so as the speed increases, the application rate begins to drop off. A narrower spray width would help eliminate this problem because the smaller diaphragm pumps used on ATVs don't have the capacity to maintain the application rate over such a wide swath. The flowmeter's accuracy was verified before performing the constant-rate test.
Herbicides can only be applied at a constant rate if the applicator does a perfect job of spacing the distance between spray swaths. This becomes more difficult with a boomless sprayer. Because the swaths are relatively wide, it is difficult to see tire tracks or dye markings from previous swaths. At slower speeds, the spray width decreases for a boomless nozzle because pressure drops.
