Chapter 20

Fertigation in Greenhouse Production

Venturi Fertigation Injectors

Venturi injectors are relatively easy to use, and their cost is low, but they are affected by water pressure. The simplest volumetric injector is based on Venturi devices that reduce pressure (vacuum), sucking the fertilizer solution into the line. A venturi injector is a tapered constriction, which operates on the principle that a pressure drop results from the change in velocity of the water as it passes through the constriction. As water flows through the tapered venturi orifice, a rapid change in velocity occurs. This velocity change creates a reduced pressure (vacuum), which draws the liquid from the stock tank into the irrigation system, eliminating the need for a separate chemical injection pump.

Venturi Injector Configurations

There are three configurations used with venturi-type suction devices.

First, the injector may be plumbed in parallel with a pressure-reducing valve as shown in Figure 20.1, which automatically creates a pressure differential across the injector, thereby allowing the injector to produce a vacuum and draw in material. This is a more efficient system because it eliminates the pressure drop in the mainline that occurs when a valve in the mainline is used to create a pressure differential.

Second, the injector may be plumbed in parallel with a simple, manually operated valve on the mainline circuit as shown in Figure 20.2.

Third, venturi injectors may be plumbed with a small booster pump that creates the needed pressure differential during chemical injection periods only, as shown in Figure 20.3.

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