Improperly calibrated sprayers threaten the wallet and the environment. A few minutes spent calibrating a sprayer can ensure expensive inputs go where they are supposed to and at their recommended rate. Proper calibration exposes under-pressured systems and worn tips that can sabotage a spray program and its budjet. Follow these steps to calibrate your sprayer safely and effectively.
1) The first step in any calibration effort is to check tractor speed. Mark off lengths of 100 and 200 feet for measuring tractor speeds of 5 mph and 10 mph, respectively. Fill the sprayer tank half full of water, select the engine throttle setting and gear that you expect to use when spraying, then record the seconds required to drive the length of each course twice at their respective settings. Average the results of each set and use the following equation to determine ground speed.
Speed = Distance (ft) x 60 / Time (sec) x 88
2) Record the nozzle spacing, nozzle type, ground speed and product label application rate. Check to ensure all nozzles are of a uniform type.
3)Multiply the application rate (GPA) by the speed (MPH) and the width of the spray pattern (w)* . Divide this amount by 5940 (a constant), to determine the gallons per minute (GPM) produced by each nozzle.
4) To set correct pressure, operate the water filled sprayer in place to check for leaks and stoppages. Stop the sprayer, and replace one tip on the boom with an identical new tip and strainer. Check the tip product information sheet for recommended delivery rate and pressure that matches the GPM level calculated in step 3.
Engage the sprayer and adjust for recommended pressure. Collect the volume of spray produced from the new nozzle tip over a one minute period. Measure the water, and fine tune the pressure setting until the calculated delivery rate is reached.
5) Repeat the collection procedure with several tips on each boom section. If variations in flow in excess of 10% are produced from more than one tip, replace all old tips and screens.
* If calibrating a sprayer for broadcast application, use boom length for spray pattern width. If calibrating for banding, use only actual spray pattern in inches (12 bands of 10" each on 30" rows equals spray pattern in inches (12 bands of 10" each on 30" rows equals spray pattern width of 120" on a 30' boom).
Directed applications with multiple nozzles requires that the row or band in inches be divided by the number of nozzles directed at the row to calculate w (30"/3 nozzles x # of rows = w).