Nozzle selection should not be based on “gallons per acre” as advertised by some manufacturers. A nozzle that is identified as a 10-gallon nozzle will deliver this amount per acre only for one condition, such as when the nozzle spacing is 20 inches on the boom, the sprayer is traveling at 4 mph and the boom pressure is 30 psi. If the spacing, speed or pressure varies from these set values, the nozzle will not deliver the specified gallons per acre.
Global Positioning System Technology is now available to automatically determine position using the global positioning system (GPS) . This system, developed by the U.S. Department of Defense, uses a network of 24 satellites orbiting the earth. The user must have a receiver to interpret the signals sent from the satellites and to compute its position. It works whether the receiver is stationary or mobile, anywhere in the world, 24 hours a day. Global positioning system. Signals from three satellites are required to determine a two-dimensional position on the earth. Altitude determination requires a signal from a fourth satellite. The global positioning system is in use now in aerial and ground application work and holds good potential for improved pesticide application by spotspraying patches of weeds with a chemical injection system or maintaining better swath spacing.
Roller Pumps and Controls Roller pumps consist of a rotor with resilient rollers that rotate within an eccentric housing. Roller pumps are popular because of their low initial cost, compact size and efficient operation at tractor PTO speeds. They are positive displacement pumps and self-priming. Larger pumps are capable of moving 50 GPM and can develop pressures up to 300 PSI. Roller pumps tend to show excessive wear when pumping abrasive materials, which is a limitation with this pump. Material options for roller pumps include cast-iron or corrosion resistant NI-resist housings; nylon, polypropylene, teflon or Buna-N-rubber rollers and Viton, Buna-N or leather seals. Nylon rollers are used for all-around spraying; they are suitable for fertilizers and weed and insect control chemicals, including suspensions. Buna-N rollers are used for pumping abrasive suspensions and water. Polypropylene rollers have proved to be excellent for water handling applications and have approved wear characteristics. Teflon rollers have also demonstrated multi-use chemical handling ability. Roller pumps should have factory-lubricated sealed ball bearings, stainless steel shafts, and replaceable shaft seals. The recommended hookup for roller pumps is shown in Figure 4. A control valve is placed in the agitation line so the bypass flow is controlled to regulate spraying pressure. Systems using roller pumps contain a pressure relief valve . These valves have a spring-loaded ball, disc or diaphragm that opens with increasing pressure so excess flow is bypassed back to the tank, preventing damage to sprayer components when the boom is shut off. Figure 4. Spray system with a roller pump. Figure 5. Pressure relief valve. The agitation control valve must be closed and the boom shut-off valve must be opened to adjust the system . Start the sprayer, making sure flow is uniform from all spray nozzles, and adjust the pressure relief valve until the pressure gauge reads about 10 to 15 PSI above the desired spraying pressure. Slowly open the throttling control valve until the spraying pressure is reduced to the desired point. Replace the agitator nozzle with one having a larger orifice if the pressure will not come down to the desired point. Use a smaller agitation nozzle if insufficient agitation results when spraying pressure is correct and the pressure relief valve is closed. This will increase agitation and permit a wider open control valve for the same pressure.
The agitation control valve must be closed and the boom shut-off valve must be opened to adjust the system . Start the sprayer, making sure flow is uniform from all spray nozzles, and adjust the pressure relief valve until the pressure gauge reads about 10 to 15 PSI above the desired spraying pressure. Slowly open the throttling control valve until the spraying pressure is reduced to the desired point. Replace the agitator nozzle with one having a larger orifice if the pressure will not come down to the desired point.