Pesticide Application and Equipment in Greenhouses
Types of Spray Nozzles
Spray nozzles come in various spray nozzle designs and can be classified by their spray patterns. We generally differ between hydraulic and pneumatic when talking about spray nozzles. Hydraulic nozzles only use liquid pressure, whereas pneumatic nozzles use air and liquid pressure.
Hydraulic Spray Nozzles
Hydraulic atomizing nozzles rely on water to make very fine droplets. Hydraulic nozzles rely on energy in the form of liquid pressure to force spray liquid out through the exit orifice. The designs produce a moderate rate of ow and a wide range of spray shapes and droplet sizes. There are no secondary gas or air streams used to atomize the spray. There are many types of hydraulic nozzles available for spraying pesticides.
Cone Nozzles
TCone nozzles are used primarily when plant foliage penetration is essential for effective insect or disease control and when drift is not a major concern. At pressures of 40 to 80 psi, these nozzles produce small droplets that readily penetrate plant canopies and cover the underside of the leaves more effectively than any other nozzle type. However, because of the small droplets produced and high operating pressures, these nozzles produce patterns which are very susceptible to drift and generally not recommended for broadcasting herbicides.
Flat Fan Nozzles
Flat fan nozzles are the most common type of nozzle and can be suitable for many different purposes (Figure 30.2). These nozzles have a rectangular or lens shaped orifice which produce a tapered distribution of droplets across the nozzle swath. Less material is applied along the edges of the spray pattern, so the patterns of adjoining nozzles must be overlapped to give uniform coverage over the length of the boom. Uniform coverage is achieved by overlapping each nozzle 30 percent with the nozzle each side of it. Normal operating pressure is variable depending on the nozzle used.
Turbo and Double Turbo Fan Nozzles
Turbo types are also a common type of nozzle and suitable for broadcast spraying. These nozzles have a tapered edge to give a wide-angle flat spray pattern (Figure 30.3). Uniform coverage is also achieved by overlapping each nozzle 30 percent with the nozzle each side of it. There are also many sizes of these nozzles that can be operated under various pressures to produce a wide range of droplet sizes.
Pneumatic Spray Nozzles
Pneumatic atomization uses the twin fluid principle, which combines both air (gas) and liquid inside a mixing chamber. The air (gas) is used to break the liquid into finer droplets, which creates the atomization.
Air-Induction Nozzles
Air induction (AI), (commonly referred to as air inclusion or venturi) nozzles have the same basic design feature—two orifices, one orifice to meter liquid flow, and the other larger orifice to form the pattern (Figure 30.4). Between these two orifices is a venturi or air aspirator, used to draw air into the nozzle body. In the body, air mixes with the liquid forming an air-entrained spray pattern at a lower pressure. The spray pattern is comprised of large, air-filled, coarse droplets with very few drift-susceptible droplets.
Nozzle Nomenclature
There are many types of nozzles available, with each providing different flow rates, spray angles, droplet sizes and patterns. Some of these spray tip characteristics are indicated with a four- or five-digit number designation on the tip. Remember, when replacing tips, be sure to purchase the same tip number, thereby ensuring your sprayer remains properly calibrated. For example, the TeeJet “11004 nozzle” has a 110-degree spray angle and applies 0.4 GPM at the rated pressure of 40 psi (See Figure 28.1).
Nozzle Materials
Nozzles are made from several materials. The most common are brass, nylon, stainless steel, hardened-stainless steel, tungsten carbide, thermoplastic, and ceramic. There are advantages and disadvantages with each type of material. Brass nozzles are relatively inexpensive, but they wear rapidly with abrasive materials, such as wettable powders and liquid fertilizers. Stainless steel and hardened stainless steel are the most resistant to wear, but their expense discourages some users. Frequent replacement of brass nozzles usually makes their use more costly in relation to the area sprayed.
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