Hand Sprayer Calibration
Calibrating a sprayer means making trial runs to determine the application rate. Calibrationr equires only a few minutes and is worth the time spent for several reasons. For one, the right amount of chemical must be applied to be safe, effective, and economical. Using more chemical than is needed is wasteful and may pollute the environment; not applying enough chemical also is uneconomical because the treatment is less effective.
Hand sprayers must be calibrated to ensure accurate application rates. The person who will make the application should do the calibration. The operator needs to know the application rate so that the percentage of an acre covered by a tankful can be determined. By multiplying this percentage by the recommended application rate per acre, the operator can find the amount of chemical required for each tankful. Before calibration is begun, operate the sprayer with water only to ensure that all parts are operating properly. Knapsack sprayers, handguns, and other hand sprayers can be calibrated with the following methods.
Per-Acre Rates for Broadcast or Band Herbicide
For broadcast or band spraying of herbicides, or for continuous "down-the-row" tree spraying, follow these steps:
1. Select a plot to measure and then mark the calibration distance appropriate for your nozzle spacing for broadcast spraying (width covered by a single nozzle) or your band width for applying a band. The proper course size should be selected from Table 2.2 (see also Figure 2.4). Caution: The pattern width depends on the nozzle-to-target distance. You might need to practice with water on a paved surface until you determine the proper nozzle height to obtain the desired pattern width.
2. Fill the sprayer tank with water only and spray the calibration plot at the desired pressure and walking speed. Measure the number of seconds required to spray the calibration course while walking and pumping at a comfortable, steady speed. You might want to practice with only water on a paved surface to establish your walking speed and to check for uniformity by observing the drying pattern.
3. With the sprayer in place and while pumping to maintain the selected application pressure (not applicable to powered pumps), collect the spray output from one nozzle for the same number of seconds measured in step 2. Be sure to collect all the spray output from the nozzle under test for exactly the same time period. The water in the container will be the same amount applied to the calibration course. The number of fluid ounces collected equals the gallons per acre (gpa). Example: With a 24-inch band, if it took 38 seconds to cover the 170-foot course, collect the spray output for 38 seconds. If you collect 16 fluid ounces, the application rate is 16 gallons per acre and a 4-gallon tankful will cover 0.25 acre.