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Precision Application Dependson Accurate Calibration of

Sprayers and SpreadersBy Steve and Suz Trusty

A ccurate calibration of sprayersand spreaders allows preciseapplication of material at prop-

er labeled rates in accordance with local,state and federal regulations. The rateslisted on product labels have been deter-mined through extensive research andtesting to be the most effective to accom-plish the task for which the materials arebeing applied. Using less of the productmay not accomplish that purpose and maymake a second application necessary,which is more expensive than doing itright the first time. Using more of theproduct may cause damaging side effectsand definitely will be more expensive.

SPRAYERSHand-pressurized and powered

sprayers both operate on the same basicprinciples. Start with clean and well-maintained equipment prior to calibra-tion on both types of sprayers. Calibrateboth types using plain water.

Hand-pressurized sprayersMake sure spray tips are clean. Spray

water through the tips to visually checkthe delivery pattern. On individual tips,check for clogging or uneven deliveryof material. Then fill the sprayer tank witha premeasured amount of water, generally1/2 to one gallon.

Pressurize the unit, but be consis-tent. For example, always pump 15times. Once the unit is pressurized,start spraying in a premeasured area ofknown size. For handheld or backpacksprayers, the best size for a premea-sured area is 1,000 square feet. Spray theentire premeasured area.

Then pour the water left in the sprayerinto a clean container and measure theamount. Subtract the leftover amount

14 sportsTURF

from the beginning amount. The dif-ference is the amount of material actu-ally sprayed based on the walking speedof the person spraying and the pres-sure level to which the sprayer was set.This determines the amount of liquidsprayed per the premeasured area of thesite. Repeat this entire procedure threetimes to develop consistent results.Always calibrate and spray under stan-dard conditions, with winds of 10 milesper hour or less.

Power sprayersTo check calibration accuracy, check

the output of each individual nozzle.First, adjust the operating pressure foryour sprayer. Find the numbers on thenozzles that identify the size and style.All nozzles on the sprayer must be iden-tical. Refer to the nozzle manufacturer'scatalog for information on that nozzle.Each specific nozzle will be rated forthe capacity of the nozzle in gallons perminute (GPM) at a certain pressure inpounds per square inch (psi). For exam-ple, a nozzle may have a capacity of .28GPM at 20 psi; the same nozzle could havea capacity of .45 GPM at 50 psi.

Calibrate the sprayer by referringto the catalog for the correct pressure set-ting and the GPM capacity for the noz-zles. Adjust the pressure regulator valveto the desired pressure. To avoid exces-sive wear in actual spraying conditions,run the sprayer at the lowest pressuresetting possible to deliver the number ofgallons needed.

Make sure the suction-line valve isopen. Select a container with easy-to-readmeasurement marks. Set a specific timeinterval, such as 30 seconds, and catchthe water output from a single nozzle inthe container. Measure and record theoutput. Follow the same steps to check

the output from each of the remainingnozzles. Compare the output as deliveredby each nozzle.

Any tip with a variance of plus orminus 10 percent should be replaced. Oncetips are replaced, repeat the procedureto recheck output accuracy. Continuechanging tips until all are within theacceptable, less-than-10-percent range.

When the nozzles are operating prop-erly, recheck the degree of overlap spec-ified by the manufacturer for that noz-zle size and type. For example, somenozzles have a 100-percent overlap spec-ified, meaning that each nozzle sprayson each side to the center of the nozzlenext to it.

After these adjustments have beenmade, arrange to test the accuracy of thespray pattern along the boom by oper-ating the water-filled sprayer on a dryportion of an unused paved area, such asa parking lot, with no visible wind move-ment to alter the spray pattern. Makeadjustments as indicated by the spraydelivered and recheck for accuracy.

In actual operation, it is essentialthat the sprayer deliver the preciseamount of material per acre (or per1,000 square feet) recommended by theproduct manufacturer. The ground speedat which the sprayer travels iscombined with all the other factors ofthe nozzle operation to determine thisapplication rate.

If your sprayer is not equipped witha spray monitor, you'll need to set groundspeed for accurate application of mate-rials. Measure a set distance on a sur-face similar to that on which spraying willtake place. For example, mark off 100 feetfor speeds up to five miles per hour;200 feet for speeds ranging from five to

continued on page 16

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Speaders & Sprayerscontinued from page 14

10 miles per hour. Base the width of thepremeasured area on the width of thespray boom. The measuring area shouldgive the equipment a "straight shot"run span appropriate to the type ofsprayer being calibrated.

Fill the sprayer tank. Select the gearsetting that will be used and run atwide-open throttle at all times. Thenoperate the unit through the measuredarea in each direction. Turn the sprayeron and off while at operating speeds andtime the spray interval from the begin-ning to ending point. Average thesetimes. Use the equation or chart below todetermine ground speed. With a spraymonitor, this determination is done for you.

Repeat this procedure three timesfor accurate measurement of time anddistance. Now that you have determinedthe time it takes to cover the premeasuredarea, measure the volume of outputfrom each spray tip for that same timeinterval. Add the total output from eachof the tips to find the total liquid sprayrate. That total is the volume of spray thatactually will be delivered over the des-ignated area. Again, repeat the procedureto ensure consistency and accuracy.

Individual walking speed may influence the proper calibration of walk-behind spreaders.

With the calibration volume known,you can now mix material according tothe calibration rate. To fill a powersprayer with a known output — say100 gallons per acre — read the productlabel to find the amount of materialthat should be applied per 100 gallonsor per acre.

Seasonal Pre-Spray Preparation

Before using a sprayer, check it thoroughly. Inspect the pumpbearings, seals and drive. Turn the pump sheave by hand. If itdoesn't move freely, bearings may require replacement. Look forany leakage around the seals. Replace parts as necessary. If thepump is belt-driven, check the belt condition. Replacing the belteach spring as part of the preparation process may be best.

Make sure all safety shields are installed properly.Check the tank for corrosion, scale and foreign material. Theseproblems will be more likely if proper cleanup procedures werenot followed prior to seasonal storage. If problems exist, add acleaning agent such as household ammonia or detergent to thewater when f i l l ing the tank. Remove the drain plug,completely flushing the solution from the tank. You may needto repeat this process several times. Fill the tank with clear waterfor a final rinse.

Remove the suction line and pressure line strainers forinspection and cleaning. Clean with water, detergent and abrush. The basic function of these strainers is to save thesprayer from damage. If they are penetrated by sand or otherimpurities, they may plug the pump or clog the sprayer. If the suc-tion strainers become plugged, the pump may be starved for fluidand could pump air, damaging the system. Cracked,damaged or broken strainers must be replaced.

Examine the suction hose from the strainer to the pump. Ifthis collapses inadvertently, it could impede fluid flow. Replaceas necessary.

New spray nozzles and screens (if your sprayer is equippedwith screens) should be installed to ensure spraying accuracyfor the start of the season. Make sure nozzle placement iscorrect. Follow the recommendations of the nozzle manufacturerfor the proper degree-angle nozzle tilt for the nozzles used.

Keep one unused nozzle from the new set to compare for noz-zle deterioration at appropriate usage intervals (daily,

weekly or monthly) for the chemical(s) being applied. Lack of sprayuniformity is commonly caused by nozzle wear. Theorifice becomes larger due to the abrasive action of thematerials passing through it, in turn causing increased oruneven output from that nozzle.

Examine the sprayer hoses and piping for weatheringcracks, kinks or damaged areas. If the suction hose appears wornor collapsed at any location, replacement is recommended.Because downtime is so critical during the rush of the season,many maintenance supervisors prefer to replace sprayer hosesas a standard procedure during seasonal preparations.

Reinstall the spray monitor (if equipped) and flow meter.Reinsert all drain plugs that have been removed during seasonalstorage. Check to ensure that all drain plugs fit properly andsecurely. Lubricate all bearings.

Fill the sprayer tank with water. A tank full of wateris used to verify if any leaks are present and can be used forcalibration. Make sure nozzle size, nozzle spacing, flow rate andspray pattern are uniform across the boom.

Information supplied by the nozzle manufacturer willshow the precise amount of water a specific size and type ofnozzle will deliver at a given pressure so that calibration may bemeasured precisely. With a spray monitor, calibration is set byprogramming the rate of application following this information.

Check calibration accuracy. Check that proper safetyprecautions have been taken to ensure operator safety and pre-vent contamination of the water source. Anti-backflow devicesand check valves must be installed on pumping andfilling equipment. Chemical-resistant clothing, gloves, hardhat, boots, goggles or face shield, and a respirator areappropriate items a sprayer operator should wear. Thesprayer should be equipped with a freshwater tank for usein case of a chemical splash and for rinsing the operator'sclothing after each use.

GRANULAR SPREADERSGranular spreaders can be centrifu-

gal-type or drop-type. Drop spreadersdeliver material along the base of the hop-per directly to the ground below.Centrifugal spreaders deliver materialfrom the base of the hopper onto a dis-pensing device that rotates, throwing thematerial in a curving pattern over adistance to the right, front and left of thespreader hopper.

When calibrating either type, alwaysstart with clean equipment. Have a pre-measured area of known dimensions.Calibrate the equipment with the mate-rial that will be applied. Use an amountof material realistic for the size of thespreader, enough to achieve a proper flow.

Drop SpreadersPlace the material in the spreader hop-

per. Start with some calibration numberor letter. This will be easier if you havesome experience with the material or ifthe product label gives a suggested cal-ibration setting. Otherwise, the startingpoint is a random choice.

With drop spreaders, devices can beattached to the base of the spreader tocollect output to measure for calibrationdetermination. Without such a device, useplastic sheeting or butcher paper to col-lect the material. Walk a known, pre-measured distance over this material,opening and closing the spreader while

16 sportsTURF

walking at a normal, steady pace. Gatherthe material spread, pour it into a mea-suring device and weigh it. Be sure todeduct the weight of the measuringdevice from the total.

Once you know what rate thespreader is delivering material, you cancompare that rate to what should beput down. Use the following formula:

rate X areaanalysis of material

(for example .38 for 38percent N)Adjust the calibration number or let-

ter up or down until the proper outputrate is achieved. Once that calibrationhas been reached, repeat the measure-ment process two or three more times forconsistency and accuracy.

Centrifugal SpreadersCentrifugal spreaders have varying

kinds of adjustments of distribution.The distribution pattern should be con-sistent, not skewed to the right or left.The peak of the pattern should be alignedwith the center of the spreader.

Determining if a spreader is throw-ing more heavily to the left or right bysight alone may be difficult; however, kitsare available to measure the patterns ofsome spreaders. For an accurate checkwithout a kit, run the spreader across aseries of boxes or grids that reach acrossthe distribution swath to catch the mate-rial delivered. Measure the materialcaught in each container to determineinconsistency.

Most centrifugal spreaders have someform of adjustment to correct patternskew. The main goal is to make thedistribution pattern as even as possibleso that the rate of material appliedwill be the same across the swath ofthe spreader.

Again, when checking calibration,use a sufficient amount of materialto ensure proper flow. Weigh the amountof material put into the hopper. Baseyour initial calibration setting on prod-uct label recommendations if theyare available.

To cover the premeasured area, workrom the outside pass to the inside

passes. Open and close the spreader^hile moving at a normal, consistent rate.

With centrifugal spreaders, speed ofmovement is important: The faster thespreader moves, the farther the materialis thrown. At a slower rate of move-ment, less area is covered with each

continued on page 18

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Circle 105 on Postage Free Card June 1995 17

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Speaders & Sprayerscontinued from page 17pass, and a heavier rate of material isapplied. On walk-behind units, theaverage swath — and therefore theaverage pass — is 6 to 8 feet. Position eachpass so that the leading edge of theswath of the material applied is thrownback to the wheel prints of theprevious pass.

Once the area has been covered, pourthe material remaining in the hopper intoa measuring device and weigh it.Be sure to deduct the weight of thecontainer. Subtract the amount of mate-rial remaining from the amountinitially placed in the spreader. Comparethe amount of material actually appliedto the label application rate. Use theformula shown above.

Reset the application rate up or downto reach the proper calibration rate foraccurate distribution. Once the accu-rate setting has been reached, repeat theprocedure two or three more times toensure accuracy.

Because material will be applied witheach checking process, have multiplepremeasured areas on which to apply theproduct. If a deflector shield is to be

used for the outside pass with a cen-trifugal spreader, check calibration withthe deflector attached. Then make appro-priate adjustments in the application ratesto ensure proper material delivery.

Large, pull-behind spreaders are cal-ibrated in the same manner as smaller,walk-behind units but on a bigger scale.Because emptying a bigger hopper canbe difficult, the amount of material leftin the hopper usually can be determinedfrom measurement markings inside thehopper or from the difference in startingand ending weight of the total unit.

Adjust for IndividualsBecause each person walks at a dif-

ferent rate, each should calibrate walk-behind spreaders or handheld and back-pack sprayers individually to arriveat an accurate calibration. Using a tonalstop watch can help set a more consis-tent walking speed for all personnel.

Once calibrations are set, cross-checkthem throughout the day. Ideally,this would be done at the beginning ofevery application. Realistically, checkonce or twice during the day on areaswhere measurements are known toensure accuracy.

Equation for DeterminingGround Speed:

Distance (feet) X 60

Time (seconds) X 88

Chart for Determining

Speed in MPH

0.51.01.52.02.53.03.54.04.55.0

Speed (MPH)

Ground Speed:Time Required in Seconds to Travel

100 fe

1368463427232017

1513

et 200 feet

2721369268544640343028

aOOjeet4092051361038268585

4641

Accurate application is to everyone'sbenefit. When applications aredone right the first time, results willbe more consistent and money will notbe wasted. •

Compiled from STMA seminarpresentations, with special thanks for infor-mation provided by Steve Griggs, branchmanager of the TruGreen I ChemLawnSan Diego Branch, and Don Lindenfelser,field service coordinator for John Deere'sGolf and Turf Division.

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18 sportsTURF Circle 106 on Postage Free Card