Boom sprayer calibration tips
Generally, when preparing the spray mixture, fill the tank more than half full of water and pour in the correct amount of chemical while the pump is running. Then, finish filling the tank. When using wettable powders, make a slurry in a separate container and then add the slurry to the tank to ensure good mixing.
Here are some other considerations for calibrating your sprayer:
- Getting the right amount of chemicals on the ground is not enough to achieve effective pest control. How the chemical is deposited on the spray target is as important as the amount deposited. Make sure that all nozzle tips are properly aligned. Some nozzles require overlapping adjacent spray patterns. Check the nozzle catalog to determine the overlap required for a given type of nozzle.
- A common cause of non-uniform coverage is clogged nozzles. Watch the nozzles periodically while spraying to detect clogging. Always carry extra nozzles in your tool box, and replace bad nozzles with good ones immediately.
- In most cases, the pressure gauges on sprayers do not represent the actual pressure at the nozzle tip. Therefore, check the pressure at the nozzle tip when calibrating your sprayer.
- Safety is extremely important when working with chemicals. Always wear gloves and protective clothing when handling chemicals and calibrating sprayers. For safety reasons, use water instead of actual chemical mixtures when calibrating.
However, some carriers, such as liquid fertilizers, are much denser than water and may cause the nozzle flow rate to vary from the rate obtained with water. In this case, determine the average nozzle output using the actual chemical mix in the field, away from the farmstead.
- To determine the actual travel speed in the field:
Distance (feet)/ Travel (seconds) X 0.68 = Travel speed (mph)
- To determine the appropriate travel speed (MPH) for a desired application rate (GPA):
a. GPA2 X MPH2 = GPA1 X MPH1
b. MPH2 = GPA1 X MPH1 / GPA2
- To determine the appropriate pressure (PSI) for a desired application rate (GPA):
a. GPA2/GPA1 = (sq.rt. PSI2)/sq.rt.PSI 1
b. PSI2 = PSI1 X (GPA2/GPA1)2
GPA2, GPA1: Desired and measured application rate, respectively (gal./A.).
MPH2, MPH1: Desired and measured travel speed, respectively (miles/hour).
PSI2, PSI1: Desired and measured spraying pressures, respectively (lb./in.2).
The author acknowledges the useful suggestions given by T.G. Carpenter and J.A. Gliem of the Department of Agricultural Engineering, Ohio State University.