When filling a spray tank with a hose, do not allow the hose to go inside the spray tank. An applicator should always maintain an air gap between the end of the hose and the chemical in the tank. If for some reason water pressure is lost while the end of the hose is in the tank, back-siphoning can occur. In this case pesticides can flow from the tank into the water lines. A backflow prevention valve may prevent contaminated water from getting into a well or municipal water, but it would still be in the water lines. Maintaining the air gap between the end of the hose and the chemical in the tank would prevent this from happening.
Calibration
Calibration is an extremely important step of pesticide application. It is possible for two people to mix pesticide in two tanks the exact same way and apply a different amount of pesticide per acre. Different tips, different pressure, and different speed can change the rate of pesticide being applied. Proper sprayer calibration will determine the amount of water being applied per acre. Once the applicator determines the amount of water that is being applied per acre, they will know how much pesticide to apply to the tank.
Contact your local Extension office if you have questions about sprayer calibration. There are existing publications and videos that will explain the process step-by-step for all types of equipment including air blast sprayers, boom sprayers, boomless sprayers, granular applicators, and backpack sprayers.
Lots of information can be found on a pesticide label. It is important for an applicator to read and understand how to correctly use a product. Contact the local Extension office with any questions about pesticide safety.
Source : aces.edu