How to Calibrate a Knapsack Sprayer Correctly for Effective Usage

how to calibrate a knapsack sprayer

Last Updated on May 12, 2021

Originally designed for agricultural and farming purposes, a knapsack sprayer is a useful product that quickly finds its way into consumer gardens. The average sprayer makes it much easier to deliver a large amount of water to space at a fantastic application rate.

One of the most important things you can do is learn how to calibrate a knapsack sprayer correctly. Today, we’re going to introduce you to the basics of calibration.

What is Knapsack Sprayer Calibration?

Calibrating your knapsack sprayer reduces the number of times you’re left unable to complete a pesticide application due to not having the right resources.

Calibration means that you prefer your knapsack spray to deliver the right amount of water for several tasks. You’ll need to know a few things before you get started, including the output of your sprayer per minute. You can usually find this spraying speed information on the device.

You’ll also need to think about the walking speed of the person spraying the lawn or garden space and how many metres they’re covering with each spray. The ‘width of pass’ or swath width when working with pesticide makes a difference to calibrating.

How to Calibrate a Knapsack Sprayer

You can check your manufacturer’s instructions for an example of how to apply pesticide correctly. You can also use our guide below to do your calculations.

Your Walking Speed

To calibrate your knapsack sprayer, first assess your standard walking speed. Measure a distance of around 100 meters and put the knapsack you’ll use on your back. Begin using the nozzle while walking at a steady pace, spraying the nozzle at knee height. Time yourself in seconds to reach the end of the 100 metres, then complete the same pass again. Take an average from the two passes.

Calibration Formula

The formula for calibration is 360 (a constant figure) divided by the time it takes to travel the 100 metres. For instance, 360 divided by 75 seconds would be 4.8 Kph.

Measure the Output

Measure the output of the sprayer. You can do this by first waiting for your tank to get up to pressure. Then, release the trigger and hold the nozzle into a jug for a minute. You can then assess how much water you’ve added to the jug over that minute. Testing this several times to get an average is a good idea. For instance, if your single nozzle sprays around 1.3 litres per minute, you’ll have a general output for your single nozzle.

Remember, the amount of water you’re spraying will differ depending on your nozzles. If you’re using a double nozzle, multiply the single nozzle output by two. You can also check the label on your knapsack sprayer for more information.

Swath Width

Finally, calculate the swath width by walking across your driveway when dry. Ensure your sprayer is up to pressure, and try spraying in the normal way you would, turning from left to right slowly. You can spray for around ten strides, then measure the wet patch of ground with a tape measure to get the width.

Preparing to Spray Your Garden

Calibrating your sprayer makes it easier to determine the rate you’ll finish your task and how many chemicals you need per acre. Though it can take a while to determine this number per nozzle and application, it’s a great way to save money and time.

Once you have an insight into the factors involved during a knapsack calibration, you can begin to look into the amount of chemical concentrate you will need to fill the sprayer. It is the amount of pesticide spray, herbicide, fungicide, or any other chemical you’re using.

Finding the Amount of Chemical Needed

You’ll need to multiply the tank capacity by the dose rate for calibration purposes and divide it by the spray volume. You can get the spray volume by looking at the amount of water and chemical you can spray in a single minute. This formula will give you an overview of the amount of chemical you need. To get an insight into how much of a square space one tank will cover, you’ll need to divide the spray volume by your tank capacity.

For example, a spray volume of 15 litres divided by a tank capacity of 200 litres would create a total tank coverage of around 13.33 hectares of crops. Divide the square metres in a hectare (1000) by the tanks for the number of hectares to get an insight into how much square meterage of crop you can cover after you’re done calibrating.

Doing these calculations ahead of time should give you a good insight into the amount of chemical and water you need to cover your lawn or crop without wasting any excess liquid. You can usually get extra guidance on the label from the manufacturer about how to calibrate for the best cover. If you can’t find this information, ask the operator for guidance.

After Calibrating Your Knapsack Sprayer

Often, it takes a while to be certain that you’re getting the sprayer calibration correct. It’s easy to multiply a number incorrectly or make the wrong assumption about water pressure, target acre coverage or water to chemical ratio. The best way to improve your calibration over time is to make notes when you calculate and correct yourself every time you cover the distance of your field or garden with your pesticides.

Industry Standards

If you’re working for a company to apply pesticides, water, or herbicides to a specific location, the industry might have some standards for you to follow. Make sure you’ve measured the area carefully to reduce your risk of mistakes. You can get support from a friend to help measure if you’re struggling to time the seconds or check the volume correctly.

Recalculate, Recalculate, Recalculate

Remember that it’s best to do the measuring part of the process a few times. It is required because you can get different results when applying your product at a different height or rate. You can also see how fast you travel from one time to the next and how much of an area you cover.

Fill the Sprayer

Once you have calibrated your knapsack sprayer, and you’re sure you know how much chemical and water is required, it’s time to half-fill the sprayer with water and add the needed chemicals. Cover around half of the area that you need to treat with the formula you’ve used applied.

You should find that you cover exactly half of the area if you’ve calculated all of the seconds and product requirements correctly. If your calibrations are incorrect, you may need to use a meter stick, calculator, or other tools to check again. Before you use your tools to recalibrate, you may need to finish the application in your chosen area.

Knapsack Sprayer Calibration Tips

Get the Right Ratio

Learning how to fill and calibrate your knapsack sprayer correctly can save a lot of time and effort. There are international standards for applying these formulas if you’re uncertain. Take the time to check your workings carefully before you start to walk around with your sprayer. The last thing you want is to walk back to your home to fill the tank again and discover you don’t have enough chemical to complete the full job.

Sprayers often work best when you put the work into ensuring you can use the chemical on the full patch of grass or lawn at the same time. Applying a product at different times can lead to patchy results.

Know Your Nozzle

Remember, the nozzle you use to apply your chemical to the garden area and the size of the product you use for the application will affect the application rate. Every time you use a new nozzle or change something about the application, you will need to apply your formula and do the full calculations again.

If you have a few nozzles, you frequently use to apply formulas, consider doing the full calculations for usage rate and target chemical levels in advance. It will help you to determine what you need for each job in advance, so you don’t have to go through complex calculations as often.

Top It Up

Learning how to calibrate a knapsack sprayer means you’ll need to ensure that your knapsack sprayer works correctly. From choosing the right chemical for your needs to learning how to balance your spraying, there are various points to think about. 

Have you used a knapsack sprayer before? Have you tried calibrating it? Tell us about it in the comments.

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