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Boom Sprayer Calibration

CALIBRATION OF BOOM SPRAYERS

(Adapted from: Boom Sprayers
D. R. Daum and T. F. Reed
The Pennsylvania State University)

Manufacturers rate their nozzles both as to individual delivery and in gallons per acre based on pressure, nozzle spacing and sprayer speed. However, actual field delivery can be quite different than manufacturers ratings due to factors such as inaccurate pressure gauges and speed indicators, friction losses in the plumbing and/or wheel slippage.

Calibration tests check performance under actual operating conditions. Before calibrating, select an operating speed and pressure. Note the tachometer reading or mark the throttle setting. When spraying be sure to use the same speed and pressure as used for calibrating. There are many ways to calibrate; two simple methods follow:

Spray An Acre Method

This method requires the applicator to stake out an acre (approximately 208' x 209'), fill the sprayer brimful of water, spray the acre at the preselected speed and pressure, then carefully measure the amount of water needed to refill the sprayer to the brim. The number of gallons to refill is the gallons per acre applied.

Jar Method

Either a commercial calibration jar or a home-made one can be used. If you buy one, carefully follow the manufacturer's instructions. Make accurate speed and pressure readings and jar measurements. Make several checks. Keep in mind that you are collecting less than a quart of liquid to measure an application rate of several gallons per acre for many acres.

Any one-quart or larger container, such as a jar or measuring cup, if calibrated in fluid ounces, can be used in the following manner:

  1. Measure a course on the same type of surface (sod, plowed, etc.) and the same type of terrain (hilly, level, etc.) as that to be sprayed, according to the nozzle spacing on the boom as follows:

    Nozzle spacing (in.) 12 16 20 24 28 32 36 40
    Course length (ft.) 340 255 204 170 146 127 113 102

    You may want to set permanent stakes or paint two fence posts a different color so this step won't need to be repeated next time.

     

  2. Time the seconds it takes the sprayer to cover the measured distance at the desired spraying speed. Average several runs.

     

  3. With the sprayer standing still, operate at selected pressure and pump speed. Catch the water from each of several nozzles for the number of seconds measured in step 2.

     

  4. Determine the average output per nozzle in fluid ounces. The ounces per nozzle equals the gallons per acre applied for one nozzle per spacing. If two (or three) nozzles per spacing or row are used, multiply the average nozzle output by two (or three) to get the gallons applied per acre. For example, if your nozzles are spaced 20 inches apart on the boom, lay out a 204-foot test course.

Determine the time required to drive that distance at the desired spraying speed; say it takes you 35 seconds (about 4 m.p.h.). Next collect the 35 second flow from 3 or 4 nozzles and average. The course length times the nozzle spacing (width) equals 1/128 of an acre.

There are 128 fluid ounces of liquid per gallon. Therefore, the average nozzle flow can be read directly as gallons per acre applied. If the average from the nozzles is 24 fluid ounces, the sprayer is applying 24 gallons per acre.

See the Northeast Pesticide Applicator Core Training Manual, p. 72 for another method of boom sprayer calibration.