HOW TO: CALIBRATE A SPRAYER
Calibration is sometimes considered a tricky matter involving formulas, charts and conversion factors. But you can complete a thorough calibration for boom sprayers, backpack sprayers and spray guns in only a few steps. Calibration steps vary for each sprayer types. The following information details the specifics for each.
A. Backpack sprayers
Add a measured amount of water to the sprayer.
Spray an area measuring exactly 1,000 square feet (for example, 20 × 50 feet). Maintaining a constant walking speed, hold the nozzle steady at a constant height and either walk back and forth or move the nozzle with a sweeping, overlapping motion.
Measure the amount of water still in the tank. Subtract this amount from the amount with which you started. The difference between the two measurements is your application rate in gallons per 1,000 square feet.
B. Lawn care spray guns
Check flow rate by collecting liquid from the gun for 1 minute.
Measure the time required to spray 1,000 square feet.
The time required to spray 1,000 square feet × flow rate = application rate in gallons per 1,000 square feet.
Adjust application rates by changing pressure or application speed.
C. Boom sprayers
Check your sprayer speed. Mark a 100- or 200-foot strip of turf. With tank half full, record the time required to drive the course at your desired throttle and gear settings. Be sure to bring the sprayer to speed before you pass the start marker. Convert time to miles per hour, then identify and record the correct throttle and gear setting.
Record your set-up before spraying. For example, assume you are going to use a nozzle with a flat-spray tip to spray 21 gallons of material at 4 mph. (Make sure all tips on the boom are identical). Then record the set-up as: Application volume: 21 gallons per acre or 0.48 gallons per 1,000 square feet; Spray speed: 4 mph; Nozzle spacing: 20 inches
Calculate your required nozzle output. To determine nozzle output in gallons per minute (gpm), use one of the following formulas:
gpm = gpa × mph × W/5,940 or (gallon per 1,000 square feet) × mph × W/136
gpa = recommended gallons per acre from product label
mph = your actual sprayer speed
W = width of nozzle spacing (or spray width in inches for single nozzle and boomless spraying)
Note: The denominators — 5,940 and 136 — are unitless constants that remain the same in their respective equations regardless of other values.
Set the correct pressure. First, turn on the sprayer and check for leaks; inspect and clean tips and strainers with a soft-bristle brush. Then check the appropriate tip selection table and determine the pressure needed to deliver the target flow rate calculated from the formula in Step 3 for your new tip. Finally, turn on the sprayer and adjust it to the desired pressure.
Check for target flow rate. Do this by collecting water from one new nozzle for 1 minute. Then compare the volume of this nozzle to your target flow rate in Step 3 (0.28 gpm in the example). Make any fine adjustments to the spray volume by adjusting the pressure. Next, check the flow rate of several tips on each boom section. If the flow rate of any tip is 10 percent more or less than that of the manufacturer's specifications, recheck the output of that tip. If only one tip is faulty, replace it with a new tip. However, if a second tip is defective, replace all the tips on the entire boom. Two worn tips on the same boom indicate tip-wear problems. Once you have replaced all the appropriate tips, your system is ready for spraying.
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