When purchasing components for a constant-rate sprayer, it is important to select a pump that can produce the pressure and flows required for the number and type of nozzles you will be using. Some pressure will be lost from fittings and hoses. The typical hose and fittings from the pump should be ½ inch in diameter. Branches to individual nozzles should be 3∕8 inch in diameter.

A good fluid flow calculator can be found at: http://www.gates.com/industrial/pressure/fluidflow.cfm?location_id=3044. A pressure loss of 5 pounds per square inch through hoses and fittings would be too much. Don't try to get by with a pump that barely meets the minimum requirements.

Try to maintain the manufacturer's recommended nozzle pressures to ensure the spray has droplets of the right size and produces the proper patterns.

Before heading to the field, find the optimal application rate by calibrating the system with water. Make sure the application rate is within the herbicide label's recommendations.

Herbicides with higher application rates will require a narrower spray swath because today's 12-volt diaphragm pumps don't deliver the flows required for wider swaths. Powdered herbicides would not work well with this system because the SHURflo 2008 pump does not have enough flow to agitate the tank's contents and the flowmeter would plug too easily.

The Spray-Mate II GPS speed sensor and electric pump driver are easy to install, although the instructions for wiring these components were a little vague. The wiring harness is long and was difficult to tuck out of the way on the ATV. When purchasing the Spray- Mate II controller, work with a Micro- Trak distributor and have them package the controller with the GPS speed sensor, Model FM 500 flowmeter, and electronic pump driver.

Programming the Spray-Mate II console was not especially difficult, instructions were clear, and changes were easy to make in the field. The calibration numbers for the Spray-Mate II's flowmeter and GPS sensor were correct and didn't require any fine tuning. It does take some time to find the application rate that will stay locked in at the high and low ends of the speed range. Once this rate is known for a given nozzle configuration and pump, the flow rate readout on the controller locks in quickly and does not fluctuate much as the applicator changes the speed of the ATV.