Dairy Excel: Spraying? Calibrate and check nozzles


Many farmers consider hiring custom spraying vs. doing it themselves at this time of year.

If we break ye old sprayer out of the shed, those deciding to spray themselves need to calibrate their sprayer.

An important task. Since many farmers do not regularly calibrate, here is a simple way to accomplish this important task.

Calibrating a boom sprayer is not as difficult as it sounds. Although there are many methods to use, the method described here is simple and requires few calculations.

It’s based on spraying 1/128 of an acre per nozzle and collecting the spray that would be released during the time it takes to spray the area.

Application rates. Because there are 128 ounces of liquid in 1 gallon, this convenient relationship results in ounces of liquid caught from one nozzle being directly equal to the application rate in gallons per acre, or GPA.

For example: If you catch an average of 15 ounces from a set of nozzles, the actual application rate of the sprayer is equal to 15 GPA.

With this method, make sure that the time used to catch output from nozzles is the same as the time it takes to cover the 1/128 of an acre.

You must travel 204 feet if you have nozzles spaced at 20 inches to cover 1/128 acre.

If your nozzles are spaced at 30 inches you will need to travel 136 feet.

Forty-inch spacing and you will need to travel 102 feet.

Tools of the trade. To calibrate your sprayer, you need a measuring tape, a watch capable of indicating seconds, and a measuring jar graduated in ounces.

A pocket calculator also will be handy.

Good luck with your calibrating. You just saved money if the sprayer was putting out too much, or you will get better weed or insect control if it was spraying less than desired.

Spray drift. More and more we are seeing some specific recommendations and requirements on pesticide labels: “Apply this product with nozzles producing fine to medium size droplets.”

What is a “fine” or “medium size” droplet? It is all about spray drift.

We expect sprayers to perform several important tasks. One of the expectations is that a sprayer should help us reduce pesticide drift to minimum while maintaining optimal efficacy throughout the application site.

Besides wind speed and direction, spray droplet size is the second most important factor affecting drift.

Each class of nozzles, even the same type of nozzle with different orifice sizes (flow rates), or the same nozzle operating under different conditions will have different droplet size distributions.

Proportions. These droplets range from very small to very large at different proportions.

To avoid drift, one should choose the best nozzle and operate it under most optimum pressure settings.

Almost all major agricultural nozzle manufacturers have recently introduced their version of low drift nozzles. These nozzles are designed to create larger droplets at the same flow rate and operating pressure than comparable conventional flat fan nozzles.

However, if operated at low pressures, some conventional nozzles can be as effective in reducing drift as the low drift nozzles operating at higher pressures.

Nozzles. Flow rate, spray pressure, and physical changes to nozzle geometry and operation can affect nozzle classification.

In other words, a given nozzle can be classified into one or more droplet size categories, depending on the selection of flow rate, operating pressure, and other operational conditions.

To determine the exact drop size classification of a nozzle under a given set of operating condition, one should always check the data given in nozzle manufacturer catalogs.

(The author is an agricultural extension agent in Stark County. Questions or comments can be sent in care of Farm and Dairy, P.O. Box 38, Salem, OH 44460.)

Boom sprayer calibration

Follow these steps when calibrating boom sprayers for broadcast applications.

1. Fill the sprayer tank with water.

2. Run the sprayer, inspect it for leaks, and make sure all vital parts function properly.

3. Measure the distance in inches between the nozzles. Then measure an appropriate distance in the field based on this nozzle spacing. (20 inches = 204 feet, 30 =136, and 40 = 102).

4. Drive through the measured distance in the field at your normal spraying speed and record the travel time in seconds. Repeat this procedure and average the two measurements.

5. With the sprayer parked, run the sprayer at the same pressure level and catch the output from each nozzle in a measuring jar for the travel time required in Step 4.

6. Calculate the average nozzle output by adding the individual outputs and then dividing by the number of nozzles tested. If an individual sample collected is more than 10 percent higher or lower than the average nozzle output rate, check for clogs and clean the tip, or replace the nozzle.

7. Repeat steps 5 and 6 until the variation in discharge rate for all nozzles is within 10 percent of the average.

8. Then, the final average output in ounces is equal to the application rate in gallons per acre: Average output (ounces) = Application rate (GPA).

9. Compare the actual application rate with the recommended or intended rate. If the actual rate is more than 5 percent higher or lower than the recommended or intended rate, you must make adjustments.

10. Adjust by changing the pressure. Lowering the spray pressure will reduce the spray delivered; higher pressure means more spray is delivered. Don’t vary from the pressure range recommended for the nozzles that you use.

Correct the application error by changing the actual travel speed. Slower speeds mean more spray is delivered; faster speeds mean less spray is delivered.

11. If changes don’t bring the desired application rate, select a new set of nozzles with smaller or larger orifices.

12. Recalibrate the sprayer after any adjustment.


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