II. SPRAYER CALIBRATION 



The mechanical equipment used in the application of herbicides is of utmost im- 

 portance to efficient chemical weed control. Even distribution of the spray solution is 

 the most important characteristic of good spray equipment. Volumes of spray may 

 vary widely (5 to 100 gallons per acre) without affecting the results if adequate coverage 

 and spray distribution are obtained. The sprayer output should be determined for each 

 particular spraying operation. The best method of calibration is to make initial ad- 

 justments to suit the machine and job requirements, and then make a trial run to 

 determine the actual output of the machine. The herbicide spray mixture should then be 

 prepared accordingly. The calibration should be repeated frequently to check for nozzle 

 orifice wear and other factors affecting performance. This is especially important 

 when abrasive solutions are used. 



Individual nozzles should be checked for accuracy of delivery. This may be done by 

 measuring the volunne of spray delivered by each nozzle in 1 minute. There are many 

 methods of calibrating a sprayer. One method is given below for calibrating each of 

 three different types. 



HOW TO DETERMINE PER-ACRE OUTPUT OF SPRAYERS 



(a) Power sprayers 



1. Fill the spray tank with water. Make sure it is completely full. 



2. Drive in a straight line for exactly 220 yards, operating the sprayer at exactly 

 the same pressure and tractor speed you plan to use in the field. It is a good 

 practice to mark that notch on the throttle. 



3. When you reach the 220-yard mark, cease spraying. Then measure carefully 

 the water used in refilling the tank (a quart jar works well). 



4. Convert the number of quarts of water used into gallons by dividing by 4, and 

 then multiply this figure by 66. Divide the result by the width in feet of the 

 strip sprayed. The answer obtained is the number of gallons the sprayer will 

 put on 1 acre when it is operated at the same settings. Example: Suppose the 

 sprayer boom sprays a strip 20 feet wide. After traveling 220 yards it takes 

 6 quarts to refill the tank. Six quarts divided by 4 equals 11/2 gallons. 

 Multiply 66 by 1 1/2, which equals 99. Then divide 99 by 20 feet (the width in 

 feet of the sprayed strip). The answer is just under 5, which is the rate of 

 application in gallons per acre. 



(b) Hand- Type Boom Sprayers 



Example: 3-gallon knapsack sprayer with a 4-foot boom. Fill sprayer and walk at a 

 steady pace, maintaining a constant tank pressure, for 110 yards. Refill tank, change 

 number of quarts required to refill sprayer into gallons, and multiply by 132. Divide 

 this figure by the width of the spray swath (4 feet). The answer is the number of gallons 

 the hand sprayer is delivering per acre at the pace walked and the tank pressure main- 

 tained. 



If too much spray is being applied, walk faster or use less tank pressure. For 

 marked changes in rate of application, it may be necessary to obtain different nozzle 

 tips. 



(c) Single -Nozzle Hand Sprayers 



Example: 3-gallon hand sprayer with single nozzle. Mark off an area 10 by 10 feet 

 {100 square feet). Fill sprayer with water to 3-gallon level and spray 100-square-foot 

 area using same speed and pressure that will be used for spraying weeds. Refill 



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