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Chemigation or Fertigation Injection Pump Calibration

Chemigation or Fertigation Injection Pump Calibration

FS230E
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R. Troy Peters, P.E., Washington State University Extension Irrigation Specialist, Department of Biological Systems Engineering, Thomas Hoffmann, Chemigation/Fertigation Technical Assistant Specialist, Washington State Department of Agriculture

Applying fertilizers and chemicals to crops through an irrigation system involves multiple factors and lots of calculations. Whether you’re calculating injection rates for center pivots or drip lines, or for weight-based or volume-based applications, the Chemigation Worksheet Series will have a worksheet for your system.

Each worksheet in this series focuses on a specific type of chemigation (or fertigation) application calculation or calibration. The worksheets are designed to help growers, consultants, and fieldmen calculate fertilizer and chemical injection rates for irrigation systems as well as provide a calibration check.

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This worksheet helps with the calculations required for a chemigation pump injection rate calibration check using a calibration check tube. The meters on most injection pumps are inexact. The actual chemigation pump injection rate changes with fluid viscosity, temperature, pump wear, supply line diameter and flow resistance, and myriad other factors. Therefore, it is important to check, or calibrate, the injection rate (Figure 1). There are many types of injection pumps that operate slightly differently. But the procedure to calculate the injection rate is principally the same. Please refer to the pump’s user manual for instructions on how to operate the pump.
Figure 1. Performing a chemigation injection pump calibration.
To check the pump’s calibration, you must have an accurate measurement of the volume pumped and an accurate measurement of the time during which it was pumped.

fs230e_eq1

This can be done two ways: using a stopwatch to time the pumping of a fixed volume, or measuring the volume pumped during a fixed amount of time. Here, we demonstrate a method that can be used with any tube, including the tank level sight tube, as in Figure 2. In our example, the injection pump rate is adjusted by selecting and modifying a percentage of the maximum rated output of the pump.

Figure 2. Applicator is measuring the distance that the fluid level changed in the external site tube during the calibration time period.
Before you begin, you need to know three things:

  1. The initial pump setting (Table 1),
  2. How much volume is pumped per inch of calibration tube length (Table 2), and
  3. The fluid level difference in the tube that you should find after the calibration pump check time period if the injection pump is calibrated correctly (Table 3).

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Copyright 2016 Washington State University

Use pesticides with care. Apply them only to plants, animals, or sites as listed on the label. When mixing and applying pesticides, follow all label precautions to protect yourself and others around you. It is a violation of the law to disregard label directions. If pesticides are spilled on skin or clothing, remove clothing and wash skin thoroughly. Store pesticides in their original containers and keep them out of the reach of children, pets, and livestock.

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