Lawn & Turf – Page 6 – Sprayer Guru

25-gallon sprayers are a common size for lawn and garden or ATV/UTV sprayers. They are affordable for many people, and they can be used in a lot of scenarios. If you are looking to build or purchase one, a key thing you will want to know is how much area a 25-gallon sprayer can cover With a 25-gallon sprayer, you can expect to cover two acres. The number of acres that a sprayer with a 25-gallon tank can cover varies depending on many factors. Your operating speed, your spray nozzle size, and your application method will all affect the amount of area you can cover. If you are using a boom or boomless nozzle setup, then you can calculate the exact number of acres you can cover quite easily. If you are spot-spraying weeds, then the amount you can cover will be a bit more difficult to pin down, as there are more variables. Calculating the Number of Acres a 25-Gallon Sprayer Can Cover In order to determine the total area a sprayer can cover, you need to determine the per-acre output of said sprayer. You can accurately calculate your sprayers per acre output if you are using a boom, which is also called broadcast spraying. If you are just spraying with a wand, it is hard to determine because there are too many variables. For broadcast sprayers, sprayers with a boom, you can determine exactly how many gallons you will use per acre. This is your “rate” or GPA (gallons per acre). There is a simple formula you can use to determine the GPA that your sprayer will produce. You will need to know the flow rate for your nozzles, your speed, and the width between each nozzle (in inches). Here is the formula: GPA = (5940 x GPM*) / (MPH x Width) *gallons per minute flow rate of your nozzle(s) Calculating GPA for Boomless Nozzles If you are using boomless nozzles instead of a conventional boom, then this formula will not work. But determining the number of acres you can cover is very simple. You will just refer to the nozzle flow chart that is supplied by the manufacturer of the boomless spray nozzle. How Do I Decide My GPA? GPA is the number of gallons of your spray mixture applied per acre. Meaning, after you have mixed your chemical with water, how many gallons of that mixture do you apply per acre. Your GPA rate will be based on the product you are using. Each chemical/pesticide will have recommended guidelines for the amount of product you need to use per acre and how much product to mix with water. Usually, this is a recommended amount of ounces per gallon. There are likely going to be different rates depending on what type of area you will spray: lawn, garden, pasture, etc. The rate may also vary depending on the specific weeds or pests that you want to kill. Determining My Spray Tip Flow Rate Every type of sprayer nozzle will be color-coded. This color indicates the orifice or nozzle tip opening size. The different sizes will put out various gallon-per-minute flow rates at different operating pressures. If you already have sprayer nozzles, the nozzle will have the tip size written on it, along with the spray angle. The color will also allow you to look up the rate in the nozzle’s chart. Determining Your Sprayer Speed Your speed is based mostly on your preference. 3-5 mph for ATV/UTV is common; some crop sprayers easily run 14+ miles per hour. Rough terrain and other conditions may dictate that you want to spray faster or slower. You will likely have some trial and error to lock in a good speed for your situation. What is My Nozzle Spacing? Measure the distance between the center of each spray tip/nozzle. They should all be equally spaced; otherwise, it will be nearly impossible to know how much you are applying. Common spacing on many premade booms is 15, 20, & 40 inches, but others are possible. How to Find The Nozzle Size You Need For Your Desired GPA What if you do not have a sprayer yet, or if you have a sprayer but you find that the nozzles you have won’t produce the GPA you want? Well, you can calculate what size nozzle you will need to use. We can calculate this based on your desired GPA, the speed you want to travel, and the nozzle spacing on your sprayer (or potential sprayer). That formula looks like this: GPM (gallon per minute per nozzle) = GPA x MPH x Width (spacing of nozzles in inches) / 5940 Example: 10 GPA rate x 3 Mph x 30 Inch nozzle spacing, divided by 5940 = 0.15 GPM This means that the nozzle size you need to use to achieve 10 GPA at 3 mph, if your boom has nozzles spaced 30 inches apart, is 0.15 GPM. Using this number, you can find a tip that will put out 0.15 GPM at a given psi. Every brand of sprayer nozzle will have a chart showing the different flow rates at given pressures. The tip size is based on an ISO standard. Each different size is color-coded. You can see in the image below that, although these spray nozzles are from different manufacturers, the flow rate is the same for both green-colored nozzles. At 40 psi, they will put out 0.15 GPM. So either tip would put out a 10 GPA in our example above. RELATED: How to Read Sprayer Nozzle Charts What Happens to My GPA if I Speed Up or Slow Down? For most spraying tasks, it is necessary to speed up or slow down. This occurs when you are close to obstacles or turning around. But what happens to your spray rate if your speed changes? If you speed up while you are spraying, your GPA rate will decrease. Your sprayer is still putting out the same amount of flow per minute, but you are covering more ground each minute. If you want to maintain the same GPA and still be able to vary your speed, you must adjust the operating pressure of your sprayer. Using a regulating valve with a pressure gauge will give you the ability to adjust the pressure on the fly. You will have to use the formula above to find what GPM will be needed at different speeds to maintain the same rate. There will be a limit to how much you can vary your speed and still maintain the same application rate. Spray tips will have a max GPM and pressure that they can produce and still maintain effective coverage. A spray tip may put out 0.20 GPM at 20 psi and 0.28 GPM at 40 psi, but if you spray above 50 psi or so, the spray pattern that is produced is too fine a mist, resulting in less effective coverage. In addition to showing the flow it will produce, every sprayer nozzle chart will also show the operating psi range, and the droplet size produced at that pressure. The droplet size produced is a major factor in spray coverage and drift. Finer droplets tend to provide better coverage, but they can drift. Coarser droplets will not drift as much, but they may not kill the weeds as effectively. Again, all nozzles will have information available that helps you determine which is right for you. In many cases, pesticide and chemical labels will recommend a certain droplet size or even a specific sprayer tip. How Do I Calculate My Per-Acre Output When Spot Spraying? Spot spraying is very common for small lawns and gardens. Even in pastures or large open properties, it is effective when you only desire to apply your chemical where it is needed. In other words, you are only going to spray a weed when you see it, rather than covering the entire property. Knowing how many gallons it will take to cover an acre is difficult to determine. But if you want to buy a sprayer solely for spot spraying and are unsure of how big your tank should be, you can still get a general idea. It comes down to the flow rate your sprayer gun/nozzle will put out, and how often you will be pulling the trigger. If your spray nozzle flows 0.30 gallons per minute. You would need to hold your spray wand trigger for more than three minutes just to apply one gallon. And you would need to spray for more than 80 minutes to empty a 25-gallon tank. This is quite a bit of time. Could you walk your property in less than 80 minutes, spraying here and there? If yes, then 25 gallons will probably be way more than you need. Ultimately, it will take some trial and error. In most instances, you are probably not going to fill your tank completely unless you know you will need to. Calculate How Many Acres Any Size Sprayer Will Cover When you know the GPA your sprayer will produce, you can accurately determine how many acres a sprayer can cover. This will help you determine how large a sprayer tank you will need. Remember that bigger is not always better. Larger sprayers are heavier when full and are more costly to purchase. If you can get by with a smaller tank, you might be better off. For information on how many acres other-sized sprayers can cover, you can check out this article that shows various other sprayer tank sizes and how many acres they can cover under different circumstances.