Undoubtedly, the number one question we get from operators is: “Which nozzle should I get”? Luckily there’s no simple answer, or we wouldn’t have jobs! The reason it’s not simple is because selecting the “right” nozzle for a sprayer is a process. It can be broken down into two steps:
- identifying the right flow rate (aka nozzle size)
- choosing a specific nozzle model (i.e. brand, spray shape, median droplet size, etc.)
It’s a big question, so it would take two weeks to cover it. For now, let’s start with the first bullet: identifying the right flow rate.
All sprayer nozzles come in standardized (ISO) sizes, and these sizes are identified by numbers stamped on the nozzle as well as the colour of the nozzle itself. The nozzle’s key characteristics (i.e. the fan angle and nominal flow rate), are identified in a format that looks like this (Fig. 1):
The 110 refers to the fan angle (110°) and the 04 refers to the flow rate. 04 means 0.4 US gallons of water per minute (gpm) at 40 psi. Each nozzle brand has a slightly different convention, but no matter how the information is presented it’s on the nozzle somewhere… with one exception.
John Deere developed their own nomenclature which, unfortunately, dropped a key digit. For example, the brown Hypro GuardianAIR is described by Hypro as the GA 110-05, showing that is has a 110 degree fan and a 0.5 gpm flow.
The exact same nozzle, on private label to John Deere, is called the “PSLDA1005”. If you have the stamina to read past the “PSLDA” part, you get to guess the fan angle. Is it 10? Is it 110? Is it 210? Sorry, but you’ll have to do what we do and consult their nozzle tables to figure it out. Please, John Deere, add all the ISO standard numbers to your products.
Nozzle colour has an ISO standard across fan-style nozzles, and we have this table to match the nozzle colour to the flow rate:
You’ll note that the nozzle we pictured earlier was “flame red”, matching the 0.4 gpm on the table. So how do we use the table to pick the right size nozzle? Well, we have to use some math, but don’t panic! We also explain this with charts and apps later in the article.
Application rate (i.e. gallons per acre or L/ha) is a function of travel speed, nozzle spacing along the boom, and nozzle flow rate. Traditionally, this has been expressed as the following formula:
This formula is famously represented in nozzle charts found in all sprayer catalogues (Fig 3). Along the left side are nozzle sizes and pressures. Along the top is sprayer speed. The body of the table contains application volume. Pick your speed, and look for your application volume in the columns. If you want to apply five gpa, you need to look for the number 5 (or as close as you can get to it), among these numbers.
The format of the chart can be confusing because it doesn’t follow a modern sprayer operator’s priorities. Usually, an operator decides on an application volume first, and this decision is not very flexible. Travel speed, decided second, has more flexibility.
We’ve therefore re-worked the table to make more sense (Fig. 4). Along the top are common water volumes. The body of the table are travel speeds. Pick a water volume at the top and follow the column underneath this value to find a speed range you’re comfortable with. To the left, the nozzle size and corresponding operating pressures are now visible.
Try to operate at a spray pressure that’s in the middle of the nozzle’s operating range. For an air-induced nozzle, the range is usually from 30 to 90 psi, so the middle is 60 to 70 psi. That should be the target pressure. Look for a nozzle size that delivers this pressure at your expected travel speed.
These columns can be used to work out a nozzle’s travel speed range. If a nozzle can be operated between 30 and 90 psi, for example, the corresponding speeds are listed in the same rows in the volume column. For example, say you want to apply seven gpa and think that 13 mph would be a good average travel speed. Moving down the seven gpa column, you’ll encounter 13 mph three times – the yellow nozzle at 95 psi, the lilac nozzle at 70 psi, and the blue nozzle at about 40 psi. Now use the columns to see which of these three best matches your expected travel speed range.
The yellow nozzle would allow between 7.5 and 12.5 mph from 30 and 90 psi, the lilac nozzle seven to 16 mph, and the blue nozzle 11 to 19 mph.
Some operators try to extend that range, but dropping below 30 psi will likely result in too narrow a pattern, or too coarse a spray quality, so it’s not advised.
Note that the three-fold change in pressure from 30 to 90 psi translates to only a 1.73-fold change in travel speed. That’s due to the square-root nature of the relationship, as illustrated by this formula:
This exercise applies to sprayers with rate controllers that adjust pressure to regulate flow rates. However, if you use pulse-width modulation (e.g. Case AIM Command, Capstan Sharpshooter, Raven Hawkeye, or TeeJet DynaJet) check out this article describing these systems.
There are a number of apps and websites, usually developed by nozzle manufacturers, which provide similar answers. These are also very useful, and all of them rely on the same formulas used in our new, simplified table (Fig 4). You can go here to download a high resolution version, suitable for framing, in both US and metric units.