Chemigation & Fertigation

Fertilizer Injectors Selection, Maintenance & Calibrations

By Craig Barrett

Fertilizer injectors are devices used to apply water-soluble fertilizers, pesticides, plant growth regulators, wetting agents and mineral acids to landscaped areas. However, just like other mechanical devices, proper and frequent maintenance and calibration are crucial steps to ensure optimal injector performance and, thus, healthy plants.

How Injectors Work

Injectors take a small portion of concentrat- ed fertilizer solution from a stock tank and inject it into the water line. For every part of stock solution, there are x parts of water, where “x” is determined by the injector ratio. For example, with a 1:100 ratio, one part of stock solution is mixed with 99 parts of water for a total of 100 parts of final solution (see fig. 1).

Injectors work on one of two principles: Venturi-type and positive displacement.

Venturi-type injectors use a pressure differ- ence between the water line and the stock tank to draw a concentrated solution into a faucet connect valve and mix it with water in the hose (see figs. 2A and 2B). These in- expensive injectors can be easily attached to any faucet but do not allow precise con- trol over the concentration. Because of wa-

Fertilizer injector or proportioner

fertilizer tank

Stock solution

99 parts of water

Injector ratio 1:100

Irrigation line to plants

Figure 1. Fertilizer injector or proportioner. 22 Irrigation TODAY | April 2017

1 part stock

Water line

ter pressure fluctuations, variable amounts of chemical may be injected into the hose. In addition, the injection ratios are low (typically 1:16) and therefore require a large stock tank, limiting the use of Venturi- type injectors to small growing areas.

They typically require very little mainte- nance, such as checking the screen on the suction line for clogs and periodically re- moving salt deposits from the mixing valve.

Positive displacement injectors provide consistent injection ratios for the designed flow rates over wide variations in water pressure. A measured amount of stock solution, determined by filling a specifi- cally sized chamber, is injected into the irrigation water, the rate of which is also controlled by the unit (see fig. 3). In most cases, the limiting factor in these injectors is the minimum and maximum water flow rate permissible. However, the industry offers models that can accommodate a wide range of flow rates. The injection ratio depends on the size of cylinders and the relative rate of displacement of fluid in the cylinders by the pistons. Precise control over the amount of injected chemicals, smaller stock tanks and broader injection ratios have made positive displacement injectors an industry standard.

Stock tank

5 gal 25 50

500 etc.

To get from ratios to percent: (1/50) × 100 = 2%

To get from percent to ratios: 100/2% = 1:50

Injector ratios

1:50 = 2% 1:100 = 1% 1:200 = 0.5% 1:500 = 0.2%

100 200

Figure 2A. A small brass mixing valve that screws onto the faucet and has a hose attached to it. As water passes through the injector, it creates a suction that draws fertilizer solution from a concentrate tank. It needs a minimum 35 psi water pressure for proper operation. Besides fertilizer, it can be used to dispense insecticides, fungicides and other water-soluble chemicals through a hose. (Photo credit: Hummert Int’l. Catalog 2003)

solution x parts water

1 part stock

Water line Choosing an Injector

Important factors must be considered when choosing an injector.

Operation Size The needs of small-sized operations, less than and up to 10,000 square feet, can be serviced with smaller units.

Type of Fertility Programs A fertility program should be based on the types of landscape materials, nutrient requirements of individual plants and num- ber of different species. Consider potential future expansion because this would be the most economical approach.

Water Flow Rate When selecting an injector, it is important to know your water flow rate range. Flow rates fall into three categories: low (0.05 – 12 gpm), medium (12 – 70 gpm) or high

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