An Inside Look at Nozzle Orifice Wear Water and Damage

When we travel, we look at rivers and gorges and canyons and we're told by the guides how they were formed by the erosion caused over time by flowing water.

How that water, over thousands of years, cut a path through solid rock to form the gulches and crevasses that the rivers now run through, and we're really impressed and awed at what water could do. Yet we never ever thought that the same water could do the same to the spray nozzles on our equipment.

Yes, we never realized that water, now mixed with particles of metals and ceramics, the common components of many spray materials, could wear out the orifices in the nozzles on our sprayers.

Well, it can and will. Water is abrasive, and the materials we mix into it are even more abrasive. To such an extent, that a brass nozzle's orifice will begin to wear after only 10 hours of use at 100 pounds pressure.

Nozzle wear means that the orifice of the tip, so carefully engineered to produce an optimum spray pattern becomes deformed, which distorts the spray pattern, producing droplets that are larger than intended, uneven band application and, of course, higher volumes of material per plant or per acre.

Larger droplets cause the spray material not to coat the leaf surface, but to wet it and then slide off, which means that the spray we have meant to stay on the leaf, ends up in the ground below. By producing these larger droplets, the spray machine is delivering more material (expressed in gallons per minute) which is not only inefficient, but costly.

Your Nozzles can begin to show wear after only 10 hours of use at 100 psi.

The illustrations represents three common conditions on a spray boom. The symbol CV means Coefficient of Variation. A lower CV percentage means a more uniform distribution.

To illustrate the importance of spraying with good nozzles, take the following equation:

If your nozzle orifices are showing a wear of 10% (and this is the point that most manufacturers recommend replacement) and your spray costs are $35.00 per acre, you are wasting $3.50 per acre in excess spray.

Project that to 500 acres and you are looking at a loss of $1,750.00. Now, consider that nozzle replacement would generally run you between 100 and 300 dollars, it would pay to replace your nozzles promptly, with the added bonus that you would not have to worry about poor coverage or misapplication, since having fresh nozzles would keep your machine calibrated and efficient.

Remember always replace all nozzles, not just the ones you think are worn. Another consideration to these economics is to upgrade the type of nozzle you are using to one of the newer and more durable materials. These nozzles are considerably more expensive, but also offer a much longer wear life. This alone, more than justifies the extra expense.

Originally, nozzles were mostly manufactured in brass, mainly because brass is a soft metal and it was easy to accurately machine the orifices with the existing techniques. However, because brass is a soft metal, the wear life of a brass spray tip is relatively short, especially at high pressures, and does not justify its cost.

As the metalworking technology advanced, spray tip manufacturers introduced nozzles in Stainless Steel and Hardened Stainless Steel. These tips were considerably superior in wear life to their brass predecessors and available in most styles of nozzles:

• Flat fan
• Hollow and full cones
• Solid streams
• Off-center
• Even fans
• Narrow angle
• Etc.

Because these nozzles cost up to 5 times more than their brass counterparts, growers continued with the more economic tips for two reasons:

• They were seldom told by the seller of the advantages of the longer lasting hardened tips
• They did not realize how nozzle wear would affect their coverage and application patterns.

Of course, the advantage is with Hardened Stainless Steel, as it lasts some 8 to 14 times longer than brass, whereas regular Stainless Steel will last from 3 to 5 times more than brass, which cost-wise makes it a trade-off.

In the mid-eighties, manufacturers introduced some of their nozzles in plastic. Plastic being a very economical material and easy to mold or machine, gave growers a very economical tip with extended wear because the smooth surface of the plastic reduced the effects of the abrasive components found in agricultural chemicals.

Not all nozzle types were produced in plastic and most were recommended for low pressure applications. Some plastic nozzles are still in production and are know as Polymer Nozzles. Their wear life averages 4 to 6 times that of brass nozzles, at approximately the same cost.

One disadvantage is the fact that they are delicate and can be easily damaged under normal use and require constant monitoring to assure proper calibration and pattern.

Technological advances in the late eighties made it possible to accurately produce spray tips in Ceramic. We have to thank NASA and the Space Program for this development because the the first mass produced ceramic spray nozzles were introduced by the same group that supplies the ceramic tiles that protect the Space Shuttle on re-entry.

Ceramic is an extremely hard material and nozzles are either machined or molded, depending on the manufacturer and process. Ceramic nozzles assure a much greater wear life value because they are not only harder, but the surfaces are considerably smoother than metal. Ceramic is also corrosive resistant to most chemicals used today.

Because of the complexity in their production, not all nozzle types used in agriculture are available at this time in ceramic.

However, most of the fan, hollow and solid cone and disc/core models are available from the different manufacturers and gaining rapid acceptance with most forward-thinking growers. Cost wise, ceramic nozzles in general run about 25% more than Hardened Stainless Steel, but last between 90 and 200 times more than brass nozzles.

But ceramic nozzles must be handled with utmost care and mounted with nylon strainers as excessive torque when tightening or rough handling can crack or damage them very easily. Even so, their advantages far outdo any other nozzle material and would make them the clear choice for efficient and economical operation of your spray rigs.

There are several other materials used in spray nozzles, but mainly limited to specialty applications. The following are the most current and I show their wear ratio compared to their brass counterparts as a number after their name:

• Aluminum: 1
• Monel: 3
• Hastelloy: 6
• Stellite: 15
• Silicon Carbide: 90
• Carbides: 180

The above is not included in the analysis because of their high cost to wear ratio.

At this point you are going to wonder which nozzle material is best for you.

Consider abrasion as the major factor and pressure as its partner in crime. The higher your operating pressure, the more abrasion your nozzles will be subjected to. Therefore it seems logical that a rule of thumb would be to use ceramic nozzles in high pressure situations. Because of their orifice design and durability, you will get optimum performance with ceramics at pressures over 100 psi.

You have more of a choice if you are applying herbicides (20-30psi) or spraying at lower pressures: (40-60psi). Polymer (plastic) nozzles do very well with herbicides, especially when using the "drift control" type nozzles.

For field or banding at 40-60psi I would recommend hardened stainless steel disc/core and fan type nozzles, but ceramic hollow or solid cone nozzles.

The disc/core tips in ceramic do not seem to produce a uniform pattern at lower pressures. This could be due to the depth of the orifice of almost 3/32" which gives the spray a tunneling effect which, at those low pressures, contributes to producing larger droplets in the pattern than the equivalent hardened stainless steel disc/core tips in which the orifice has a depth of only 1/64".

The bottom line of this conversation is the fact that many growers until now have not paid that much attention to calibration and proper care of their spray tips, which should now become a priority, not only from the economical point of view, but also as a tool to prevent excessive waste and contamination.