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CALIBRATION FORMULA

GPA = Gallons per Acre
GPM = Gallons per Minute 
MPH = Miles per Hour 
W    = Nozzle spacing (in inches) for boom sprayers 
       = Spray width (in inches) for a single nozzle, band spraying or boomless spraying.
 

Measuring Travel Speed:

Measure a test course in an area with similar surface conditions on the area to be sprayed. Minimum lengths of 100 or 200 feet are recommended for speed of 5 and 10 mph, respectively. Determine the time to travel the course. To help ensure accuracy, conduct the speed check with a loaded sprayer and select the engine throttle setting a gear that will be used when spraying. Drive the designated distance. Repeat at least 3 times. Take the average of the times that were measured. Use the following equation to determine ground speed.

Or

1. Set 2 markers in the field 88 feet apart. 88 feet is 1/60th of a mile.

2. Select gear and throttle setting to be used when spraying.

3. Check time in seconds to travel 88 feet. Remember, it is important to reach your spraying speed by the time you reach the first marker, before you start timing. Best results are obtained using a full spray tank of water during your check. 
 
CALIBRATING BOOM & BOOMLESS SPRAYERS

A. First Method

1. Fill the spray tank with water. Add drift control agent if it will be used during spraying.

2. Run the sprayer at the operating pressure. Measure the Swath Width(W) in inches for boomless sprayer. OR measure the nozzle spacing (W) in inches for boom sprayers.

3. Collect the spray volume from the nozzle(s) and measure the exact amount caught for 1 minute. Use the average if multiple nozzles. Record this amount in Gallons Per Minute. 

4. Determine the sprayer speed (MPH) over 200 feetdistance. Maintain the desired spraying speed and record time in seconds. (S)

5. Determine the Gallons Per Acre (GPA). If GPA ispredetermined, simply manipulate the formula to determine the unknown.

6. Calculate the amount of chemical needed per tank. 
Rate/Acre X Tank Volume (gallons)

B. Stationary Method

1. Fill the spray tank at least half full of water. Add drift control agent if it will be used during actual application. 

2. Run the sprayer at the operating pressure. Measure the swath Width (W) in inches for boomless sprayer. OR measure the nozzle spacing (W)  in inches for boom sprayers. 

3. Collect the spray volume from nozzle(s) and measure the exact mount caught for 1 minute. Use the average if multiple nozzles. Record this amount in Gallons Per Minute. 

4. Select the desired operational speed, in miles per hour, that will be used for spraying.

5. Determine the GPA being applied by the formula:

6.

 
C. Volume Method for Handguns

1. Mark off 1000 square foot area (10’ X 100’ or 20’ X 50’)

2. Time yourself, in seconds, how long it takes to spray this area using normal spray procedures.

3. Then, spray into a container, such as a 5 gallon bucket, for this amount of time in step 2. Make sure you use the same spray pressure.

4. Measure the amount in the container in gallons.

5. Multiply the number of gallons by 43.56 to get the spray volume in gallons per acre.

Example: If it takes 25 seconds to spray this 1000 sq. ft. area, catch your spray for 25 seconds in the bucket. Measure this amount, lets say it is 2.5 gallons. Multiply 2.5 gallons by 43.56 = 108.9 GPA

Say you have a 500 gallon spray tank and want to spray 12 lbs. ff Sahara per acre. Divide 500 gallons by 108.9 GPA = 4.59 acres will be covered by one full tank load. Then multiply 4.59 acres by 12 lbs. Sahara per acre = 55 lbs Sahara per spray tank to achieve your desired rate.