Calibrating Low Pressure Boom Sprayers 



George W. Hamilton 



I he effectiveness of any pesticide depends on 

 proper application of the chemical. Proper calibra- 

 tion of sprayers measures how much material will 

 be applied by the equipment under controlled 

 conditions. Calibration of spray equipment results 

 in the correct amount of pesticide material being 

 applied to a given area and provides the applica- 

 tor with the confidence of a job done right. 



Low pressure boom sprayers are the most com- 

 mon pesticide sprayer. Proper calibration of these 

 sprayers is critical to insure uniform application 

 and economical pest control without overdosing 

 and/or underdosing parts of the treated area. Op- 

 erators must be familiar with the operation of the 

 machinery they are using and follow the 

 manufacturer's directions carefully. 



Dr. lames Mitchell, UNH Extension Specialist 

 Agronomy, has developed a fact sheet titled, "Low 

 Pressure Boom Sprayers — Calibration and Care." 

 The fact sheet lists the method and steps in cali- 

 brating the boom sprayer. This fact sheet can be 

 requested by contacting Dr. James Mitchell, Exten- 

 sion Specialist — Agronomy, UNH Cooperative Ex- 

 tension, Nesmith Hall, 131 Main Street, Durham, 

 NH 03824-3597. 



The following is a summary of this calibration 

 method: 



CALIBRATION METHOD 



STEP I. CHECK GENERAL SPRAYER OPERATION. 

 Fill the tank with water and operate the pump. 

 Check for leaks, condition of hoses, proper opera- 

 tion of the pressure gauge and clogged nozzles. 



Place a container under each nozzle and collect 

 water sprayed from each nozzle for the same 

 given time. If the output varies much, check to 

 see whether any nozzles are clogged and whether 

 all nozzles are the same size. Nozzles that have a 

 flow rate greater or less than 10 percent of the av- 

 erage should be replaced. Nozzle wear depends 

 on amount of use, nozzle material and type of 

 pesticide or pesticide formulation used. 



STEP 2. CHECK TRAVEL SPEED. 

 To measure ground speed, lay out a distance in 

 the field to be sprayed. A distance of 88 feet is 

 adequate for speeds under 2 mph and 176 feet 

 for speeds between 2 and 4 mph. Select a gear 

 and throttle setting that will be used when spray- 

 ing — be sure to have the sprayer half to three 

 quarters loaded when timing. Measure the time 

 needed to travel the given distance in each direc- 

 tion and then average the time in seconds. To 

 determine the travel speed, use the following for- 

 mula: 



SPEED (MPH) = DISTANCE in FEET X 60 SECONDS 



AVERAGE TIME in SECONDS X 88 FEET 



STEP 3. MEASURE NOZZLE OUTPUT. 



1 . Collect spray from all the tips on the boom for 

 one minute while operating the sprayer in 

 place at a desired operating pressure. 



2. Compare the amount of water sprayed col- 

 lected, in ounces, from each tip on the boom. 

 Remember that any tip that delivers 10 percent 

 more or less than the average should be 

 cleaned or replaced and then repeat the col- 

 lection for one minute. 



3 Convert the average collections per tip from 

 ounces per minute (GPM). 



GALLON per MINUTE (GPM) = OUNCES per MINUTE (OPM) 



128 (OUNCES per GALLON) 



4. Calculate the delivery of the sprayer to gallons 

 per acre (GPM) 



GALLON PER ACRE (GPA) = GPM X 5940 



MPH X NOZZLE SPACING 

 in inches 



A CALIBRATION EXAMPLE 



STEP I. All nozzles were within the 10 percent 

 tolerance level of the average output. 



June & July 1993 

 27 



