Proper sprayer calibration is an important, yet often overlooked, first step in the spraying program. Calibrating your sprayer and tractor enable you to know with confidence how much volume of product and water you are applying per acre, how many acres your tank will treat between fill-ups, and how much undiluted chemical to add to your tank to achieve the proper application rate. A properly calibrated sprayer can save you money and reduce the risk of injury to the plants you are treating.
Always calibrate a sprayer using only water in the spray tank and wearing chemically resistant gloves to avoid contact with residue that may be in the system or on the sprayer.Follow these tips for calibrating a boom or boom-less sprayer. You will need a stopwatch (or watch with second hands), a tape measure, flags or stakes, and a container that can catch water and measure in ounces (for boom sprayers) or pints (for boom-less sprayers). You will also need a trash bag or piece of tire inner tube for catching water from the boom-less sprayer.
Boom Sprayer Calibration
1. Determine nozzle spacing in inches using a tape measure.
2. Calculate the length of the calibration course by dividing the constant number 340 by (the nozzle spacing in inches determined in step 1 divided by 12). For example, a nozzle spacing of 19 inches needs a calibration course of 215 feet {340/(19/12) =215}.
A few common spacings and calibration course lengths are as follows: 15 inches = 272 feet; 18 inches = 227 feet; 20 inches = 204 feet; 22 inches = 186 feet; and 24 inches = 170 feet.
3. Measure and stake off the appropriate length of calibration course based on nozzle spacing. The course should be laid out on terrain typical to what is going to be sprayed.
4. Drive the course in the gear and rpm you will use when spraying. Record the time for the first trip and repeat. Average the two times you recorded and use this average in step #6.
5. Park the tractor and maintain the same rpm.
6. Turn on the sprayer and catch water from one nozzle for the same number of seconds that it took to drive the calibration course.
7. Ounces caught = gallons applied per acre.
8. Check all nozzles. Clean or replace all nozzles that fall outside 10% above or below the average for the other nozzles in the boom.
Boom-less Sprayer Calibration
1. With the sprayer operating at typical rpm and pressure, measure the effective swadth width of spray with the tape measure.
2. A few common swadth widths and corresponding lenghts of calibration courses are as follows: 35 feet = 157 feet; 40 feet = 136 feet; 45 feet = 121 feet; and 50 feet = 109 feet.
To determine the length of a course for a swadth width not listed, divide the constant number 5460 by the swadth width in feet (example 32 foot swadth width = 5460/32 = 171 foot calibration course.
3. Mark off the appropriate lenght calibration course on terrain typical of what you plan to spray.
4. Drive the course in the gear and rpm you will use when spraying. Record the time in seconds and repeat. Take the average of both times and use this figure in step #5 below.
4. Park the tractor and maintain the same rpm.
5. Turn on the sprayer and use a trash bag or piece of inner tube and bucket to catch the water for exactly the same number of seconds required to drive the calibration course.
6. Pints caught = gallons applied per acre.
