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How to Calibrate a Backpack Pump Sprayer

Is your sprayer’s calibration costing you?

April 19, 2023

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When it comes to calibrating a backpack pump sprayer, being just close will never be good enough. Fortunately, there are steps you can take to make sure your equipment, and the results it produces, are spot on.

Backpack sprayers are effective for spraying a wide range of liquid applications, including herbicides, fertilizers, fungicides, and insecticides. Continued advancements in design and technology have made this equipment more efficient and comfortable to use.

Perhaps the biggest benefits these sprayers lend is time and money savings. The benefits of backpack and handheld sprayers include the ability to have precise control over where you apply products, but correct calibration is required to ensure you're not over or under applying.

Why is Calibration so Important?

  • Calibration is essential to the proper and safe application of control products.
  • Calibration saves you money by ensuring you’re not wasting product and you’re applying it in a way the manufacturer deems effective.
  • Proper calibration helps avoid callbacks from customers unhappy with the result too much or too little product provides.

Step-by-Step for Correct Calibration

The success of any job means starting with the right tools. In this case, the calibrating equipment you need includes stopwatch, measuring cup (w/oz. indicators) marking paint or flags, and a bucket of water.

STEP 1: Determine application pressure and timing. We recommend the 128th method. That is the time it takes to spray 1/128th of an acre with a single nozzle by measuring a test area that’s 18.5x18.5’ or, 1/128th of an acre. Fill your sprayer tank ½ full with clean water. Ensure you’re using the same nozzle you plan to use for the product application. Make sure your sprayer’s in working condition and all pieces are functioning as expected. Check to make sure the water is flowing strongly and that there are no obstructions. Otherwise, sprayer calibration may be compromised.

STEP 2: Start your stopwatch and begin spraying your application over the test area while you walk it at a comfortable pace. You will want to aim to maintain consistent speed and coverage.

STEP 3: Record the time elapsed once you’ve covered your test area. Then, use your measuring cup and begin to fill it using your sprayer with the same pressure employed to cover the test area on the amount of time you recorded.

STEP 4: Note the number of ounces within the cup once you’ve reached the time originally required to cover the test area. Repeat steps 3 and 4 and take an average of the resulting ounces. This average number in fluid ounces is equal to the gallons required per acre.

STEP 5: Finally, be sure to compare the control application rate measured in Step 4 to the rate required on the product label. If your measured rate in not within 5 percent of the recommended rate, choose an appropriate adjustment method (see Making Adjustments below) and reset your sprayer.

Adjustment Methods:

  • Pressure: If the error in application rate is less than 10 percent, adjust the pressure if the sprayer has a pressure adjustment feature. Increasing pressure will increase the application rate; decreasing pressure will decrease the application rate. Increasing pressure also may increase the number of fine droplets produced and increase drift potential.
  • Nozzle size: If the error is greater than 10 percent, change nozzle size. Use a larger nozzle for higher rate, a smaller nozzle for a lower rate.

STEP 6: Recheck the system. Once you achieve the accuracy you want, calibration is complete.

Use this information, along with the surface area of your intended turf to be treated and the application rate noted on your control product, to calculate the appropriate amount of product to mix in your sprayer.

Now You Know Why and How. Here’s Where:

If you’re in the market for a new sprayer, consider the LESCO Zero-Pump 4Gal. Backpack Sprayer and the Flowzone Typhoon Variable Pressure Sprayer.

If you’re looking for a battery powered sprayer, here are some options:

The SiteOne Associates at your local branch will be happy to answer your questions on pump sprayers and how to correctly calibrate them. Since SiteOne offers the top brand names in green industry products, having a look at a LESCO hand pump sprayer may show you just how much time and money a unit like this will save you. You can also shop online or in the SiteOne mobile app.

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