Tree Fruit & Grape Industry News, July 2000

Take Care of Your Sprayer Nozzles

Nozzles are one of the most important parts of any sprayer. In air-blast sprayers, nozzles perform two basic roles; breaks liquid flow into spray droplets and controls the output of the sprayer. Nozzles are critical to apply the right amount of spray and to get the proper spray droplets and coverage.

Nozzles are not very expensive when compared to the cost of pesticides they apply. A complete set of 26 nozzles may range from $50 to $250 depending on the nozzle material and their expected lifetime. This is likely to be less than 1% of the cost of your annual pesticide bill. Worn and corroded (rusty) nozzles must be replaced to keep your sprayer working properly.

Madeline Waring and Bert van Dalfsen, specialists with the B.C. Ministry of Agriculture, Food and Fisheries, carried out some thorough sprayer tune-ups this spring with packing house representatives in the Okanagan Valley. The condition of the nozzles was the most common area of concern.

The most common sprayer nozzles were hardened stainless steel discs and hardened stainless steel cores (swirl plates). The hardened stainless steel material is corroding (rusting) very quickly. Rust pits on the inner surface of the disc will cause streaky spray patterns and non-uniform droplet sizes and should be replaced immediately. The hardened stainless steel cores were also rusting. The cores are difficult to clean and will also cause distorted spray patterns and may reduce the nozzle output. These nozzles should be replaced due to corrosion before they ‘wear out’ due to abrasive pesticides.

The two main alternatives to hardened stainless steel and corrosion are plastic and ceramic nozzles. Plastic is a common term that may be used to describe a large class of material that include nylon, polymer, polyacetal and PVDF. There is conflicting information in the literature regarding the wear life of different materials. One source suggests that wear life can be described relative to brass as the following:

• Brass 1
• Plastic 2-3
• Stainless steel 4-6
• Hardened stainless steel 8-15
• Ceramic 70-120

While other manufacturers may rate their plastic to be equal to stainless steel or perhaps even superior to stainless steel, plastic should be considered to have a poorer wear life than hardened stainless steel. It must also be used at pressures below 200 psi. There is a trend in the South Okanagan to use plastic nozzles instead of the hardened stainless steel to avoid the rust problem. The plastic nozzles are less than one half the price of hardened stainless steel. These nozzles could be a good alternative if they are replaced at least every year or more often as they wear.

Ceramic is a much more wear resistant material and take almost 10 times as long to wear out as compared to hardened stainless steel. Ceramic also does not rust. Ceramic nozzles cost about 50% more than hardened stainless steel and are an excellent choice for sprayers on medium or large orchards. The main disadvantage with the ceramic nozzle is that it is more brittle and more readily broken if dropped onto concrete. Also if the nozzle cap is over tightened the ceramic will crack. Care is required to make sure the ceramic nozzle does not jam in the nozzle cap while threading the cap onto the nozzle body. The nozzle cap should be threaded on by hand until it is snug and then the cap tightened only a quarter turn by wrench to keep it in place. The ceramic nozzle requires an extended nozzle cap because it is thicker and a plastic gasket or plastic nozzle strainer to cushion the ceramic nozzle between the brass nozzle cap and nozzle body. Brass nozzle strainers must be replaced with plastic. The extended cap and plastic strainer has a one-time cost of about $2.50.

Nozzles should be replaced when their output increases by 15% over new nozzles. Nozzles with small holes will wear more quickly than with large holes. Cores with four holes will wear less than cores with two holes. Nozzles at the top or bottom of the boom which are often closed in young or very old plantings will wear less than those which are normally open. Thus nozzle wear on the airblast boom will not be uniform. Be sure to keep discs and cores together as a pair to avoid mixing a new disc with a worn core or vice versa. Also keep concentrate and dilute sets of nozzles together from the time that they are new to when they need to be replaced. This will enable you to measure their wear more accurately as a set.

It is a good policy to test the wear of the smaller nozzles used in concentrate spraying separately from the large nozzles used for dilute sprays. Replace the entire set of concentrate nozzles or dilute nozzles when their output increases by 10%. The easiest way to test nozzle wear is to carry out a sprayer discharge over a five to 10 minute period and measure how much water was discharged from the spray tank. Carry out a test when the nozzles are new and record the output and pressure. Re-test at the same pressure later to determine nozzle wear by comparing outputs.

Take care of one of your sprayer’s nozzles to obtain a more accurate sprayer output and better spray coverage.

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