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Juan Cabrera-Garcia
University of Missouri
Plant Science & Technology

Injector Installation and Performance Check

Juan Cabrera-Garcia
University of Missouri

February 22, 2023

minute read

In this article we will show the recommended installation design for fertilizer/chemical injectors. We will also show two methods to determine if your injector is working correctly. The article uses a mechanical proportioner as an example, but the design applies to any type of injector that has adjustable ratios.

Fixed permanent installation

Install the injection system off the mainline in a water bypass. This set up allows for clean water to flow to flush the irrigation lines or to water the crops when no injection is needed. The set up also allows water flow in case you need to maintain, repair or replace the injection system.

diagram of injector using fixed installation

Figure 1 Diagram of injector using fixed installation. Source: Dosatron, USA


Use screen or disk filters and establish a set schedule to clean the filters. The cleaning frequency will depend on the water quality.

Pressure regulator

The pressure regulator is needed if the pressure in the main line is higher than the recommended operating pressure of the injector. Also, remember that emitters in drip irrigation system have a set range of operating pressures.

Water hammer arrestor

A back flow pressure is created when you turn the irrigation system off, which can damage the injector. The water hammer arrestor captures and dissipates this pressure before it reaches the injector.

Backflow prevention

A check valve (backflow prevention) is required to prevent contamination of the water source!

Mobile cart

Growers with multiple production bays can benefit from having a single mobile injector. Each production bay needs to have the bypass irrigation lines with adapters to connect hoses. The injector needs to be primed whenever a new stock solution is used.

diagram of pull cart with injctor attached

Figure 2 Diagram of injector using standard bypass installation. Source: Dosatron, USA

Checking the injector calibration using EC (electrical conductivity) readings

I'm going to use the label instructions in the 21-7-7 fertilizer for demonstration purposes. Use the following steps with any fertilizers that you have in stock.

  • Set the injector to the 1:100 setting
  • Prepare stock solution according to the fertilizer label. In this example, I will prepare a solution to deliver 200 ppm N. According to the label, I need to mix 12.9 ounces of the fertilizer in 1 gallon of water.

Table 1 Fertilizer mixing ratios using 1 gallon of water.


According to the label, the solution coming out of the injector should have an EC of 1.04 mmhos/cm but this is based on laboratory tests using deionized water. Your water source has a natural EC so the final reading will be what is stated in the fertilizer label plus the EC of your water source (without any fertilizers).

  • Calibrate your EC meter
  • Measure the EC of your water source
  • Turn off water flow through the injection system
  • Disconnect the injector outlet from the downstream irrigation system. Attach a hose to the injector outlet to ease sample collection.
  • Prime the fertilizer injector: place the suction line in the stock solution tank and run water through the injector. Keep the water flowing and observe the solution moving from the stock tank to the injector. Once the stock solution reaches the injector, count 15 clicks (the injector makes clicks as it mixes the solution).
  • After 15 clicks, collect a sample coming from the injector outlet and measure the EC. The value should be what is stated in the fertilizer label plus the EC of your water source. It is normal for values to be 5% off the expected values.

Checking the injector calibration using water volume

  • Turn off water flow through the injection system.
  • Set the injector to 1:100. See table below for different injection ratios.
  • Disconnect the injector outlet from the downstream irrigation system.
  • Attach a hose to the injector outlet and place it in an empty 5-gallon bucket.
  • Measure 6.5 ounces of water in a cup.
  • Remove the strainer from the edge of the suction line.
  • Insert the suction line to the cup with the 6.4 ounces of water.
  • Turn on water flow through the injector.
  • The injector should suck the 6.4 ounces when the 5-gallon bucket is full.

Table 2 Ounces of stock solution injected at different injection ratios for every gallon and 5 gallons of solution exiting the injector.

% Ratio Ounces of stock per gallon Ounces of stock per 5 gallons
2 1:50 2.6 13
1 1:100 1.3 6.5
0.78 1:128 1 5
0.5 1:200 0.65 3.25

Service the injector if the values deviate from expected values. Injector manufacturers sell maintenance kits and gaskets to service the injectors.

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REVISED: February 22, 2023