Smithco Turf Spraying Guide - Manual (Page 19)

3. INTRODUCTION TO CALIBRATION
number of acceptable methods for calibrating a turf sprayer are widely available. Two methods
are described later in this guide. Calibrating simply means to adjust a set of variables on the
sprayer in order to deliver the desire amount of chemical to a known area of turf.
The variables are:
• OPERATING PRESSURE
• NOZZLE ORIFICE SIZE
• TRAVEL SPEED
• NOZZLE SPACING (Previously discussed in this guide)
The job of calibrating the sprayer consists of balancing these variables so that your sprayer delivers
the desired application rate. That is, an amount of chemical on a given area. It is expressed as:
Gallons Per Acre (GPA) (1 US GPA = .83 UK GPA)
or Gallons Per 1,000 Square Feet (GPT)
or Liters Per Hectare (LPH)
( 1 US GPA = 9.3 5 LPH)
The calibration methods chosen must take these variables into account. They must include known
ground speed (by measurement or from an accurate speedometer) and nozzle output (GPM or LPM)
from a nozzle chart or from actual measurement.
1st VARIABLE- PRESSURE: Just as pressure increases the volume discharge rate, it also
increases the application rate. Pressure must increase by 4 times in order to double the application
rate. Small pressure changes of 10 PSI ( 1.4 BAR) or less do not greatly affect performance.
Pressure is established and maintained by a pressure control valve or by a flow control valve located
on the sprayer.
2nd VARIABLE - NOZZLE CAPACITY (Volume): We have covered the different types of spray
patterns of various nozzles and made our selection of type accordingly. We now have to choose a size,
which will provide the correct application rate. Sizes are available for all requirements. Consult the
nozzle chart in this guide for your nozzle type in order to select the correct size.
3rd VARIABLE- TRAVEL SPEED: Increased travel speed decreases the application rate (GPA or
GPT or LPH). Travel speed must be safe and appropriate for the area to be sprayed.
Unlike pressure changes, which have only a minor effect on application rate, ground speed changes
have a more major and direct effect. For example: A 50% increase in ground speed means a 100%
decrease in application rate. If the vehicle does not have an accurate speedometer, correct speed
must be determined by timing the sprayer travel over a measured distance. (Refer to the page in this
guide titled, "Useful Formulas".
To calibrate a sprayer, the user must:
1. Understand the variables
• Operating Pressure (PSI/BAR)
• Nozzle Orifice Size (GPM/LPM)
• Travel Speed (MPH/KPH)
2. Set those variables using one of the proven methods available.
3. Make a trial run and measure the output (use water, not chemical)
4. Determine the output.
5. Make adjustments to the 3 variables until the output is at the desired level.
This covers the principles of what must be known to prepare a sprayer for operation.
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