Please Check My Math

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dwightevansjr71
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Please Check My Math

Post by dwightevansjr71 »

So, I just got done putting together my 31-gallon Northstar Sprayer (the 21-gallon was out of stock) and beefing it up a little like a post I saw from another guy (Pics coming later). Here is my question. I followed the video on calibrating the sprayer. In case you are not familiar, it tells you to measure your nozzle distance and height from the ground. In my case, it was 20 inches for both. Based on that number I need to drive the sprayer 204 feet and time myself. It took me 1:13. Then you run the sprayer for that amount of time and measure how much water you capture. I captured 60 ounces which equates to 60 gallons per acre. So here is where I need a compass check. There are 43,560 SQFT in an acre. 1000 SQFT represents 2.2% of 43,560. 2.2% of 60 gallons is 1.2. Which to me means I currently am spraying 1.2 gallons per 1000 SQFT. Its a little high, but I may drive a little faster or turn down the PSI a smidge. Is my math wrong?

CarolinaCuttin
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Re: Please Check My Math

Post by CarolinaCuttin »

@dwightevansjr71

N = (V * S * W) / 5940

where

N = single nozzle output in gallons per minute
V = carrier volume in gallons per acre
S = speed in miles per hour
W = nozzle spacing (or fan width for backpack sprayers) in inches

Rearrange to get:

V = (N * 5940) / (S * W)

Figure out one nozzle output in gallons per minute at spraying pressure. Nozzle spacing is 20 inches. You are walking at 2.8 ft/s which is 1.9 mph. This will tell you your exact calibration.

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g-man
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Re: Please Check My Math

Post by g-man »

40g to an acre is 1g/ksqft
60g/a is 1.5g/ksqft.

Topic Author
dwightevansjr71
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Re: Please Check My Math

Post by dwightevansjr71 »

CarolinaCuttin wrote:
Fri Jul 31, 2020 9:15 pm
@dwightevansjr71

N = (V * S * W) / 5940

where

N = single nozzle output in gallons per minute
V = carrier volume in gallons per acre
S = speed in miles per hour
W = nozzle spacing (or fan width for backpack sprayers) in inches

Rearrange to get:

V = (N * 5940) / (S * W)

Figure out one nozzle output in gallons per minute at spraying pressure. Nozzle spacing is 20 inches. You are walking at 2.8 ft/s which is 1.9 mph. This will tell you your exact calibration.
A couple of questions. Where did you get the 5940 from? What is meant by carrier volume in gallons per acre? Once I determine one nozzle output in gallons per minute, do I have to multiply that number by three because I have 3 nozzles? My goal is to achieve 1 gal per 1000sqft of output.

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Ware
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Re: Please Check My Math

Post by Ware »

@dwightevansjr71 there are many ways to calibrate, but I would just figure out how many gallons it takes to spray your whole lawn with whatever nozzle setup you are running. Capacity should not be an issue with a 31 gallon tank on a 14k lawn.

Run a few trials with only water to ensure consistency. This is also great practice to refine the route you plan to use when spraying, learn how to best navigate around obstructions, minimize unnecessary overlap, etc.

Once you know how much water it takes to consistently spray the whole lawn, that is your calibration. Just add the appropriate product dose (the amount of a specific product needed to treat 14k) to that much water and spray.

No need to overthink it. :thumbup:

Topic Author
dwightevansjr71
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Re: Please Check My Math

Post by dwightevansjr71 »

Ware wrote:
Tue Aug 04, 2020 7:11 am
@dwightevansjr71 there are many ways to calibrate, but I would just figure out how many gallons it takes to spray your whole lawn with whatever nozzle setup you are running. Capacity should not be an issue with a 31 gallon tank on a 14k lawn.

Run a few trials with only water to ensure consistency. This is also great practice to refine the route you plan to use when spraying, learn how to best navigate around obstructions, minimize unnecessary overlap, etc.

Once you know how much water it takes to consistently spray the whole lawn, that is your calibration. Just add the appropriate product dose (the amount of a specific product needed to treat 14k) to that much water and spray.

No need to overthink it. :thumbup:
I was in the Army for 29 years! We lived by KISS, Keep It Simple Stupid. I don’t know why I didn’t think about this way. Thanks.....

CarolinaCuttin
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Re: Please Check My Math

Post by CarolinaCuttin »

@dwightevansjr71 If you are fine with just spraying at whatever carrier volume this happens to work out to, just spraying water and trial and error will be fine. Lot of products have recommended carrier volume ranges, the equation helps establish a relationship between all the variables that are in play during the spray so they can be tweaked to get to your target.

Not every DIY lawn application has to be as accurate as you would see on a golf course, but some products work much better at tight carrier volume ranges. I think once people understand the equation and realize they can calibrate with a pen and paper in 5 minutes versus spraying the yard and adjusting up or down, it becomes much more useful.

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Re: Please Check My Math

Post by cldrunner »

I really like the idea of spraying your yard a few times at the pace you think you will travel.

My backyard(fast travel with no obstacles) and front yard(slow travel with ditches, poles, landscapes, circle drive) are the same square footage. My 25 gallon sprayer does not have a recirculating pump. I'm convinced that the last few gallons are more concentrated even after mixing with paint mixer for several minutes. I have several slopes so I try to make sure those are done before I get to the bottom few gallons as my spray does not do very well with the tube on the right side on a left slope. I like moving at a slower pace so most applications I make are 25 gallons for 20K sq ft of chemical.

Every yard is different!!!

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Re: Please Check My Math

Post by Hapa512 »

I was in a similar situation with spraying my PGR. I was nervous about spraying too much PGR with a back pack sprayer. I have a pretty good general idea of what the size of my area is that I am spraying. 3,500 sqft in the back yard, and about 2,500 in the front yard. I'm pretty lazy....lol So what I did was rather then just spray water, I decided to spray or apply something that would not hurt the lawn if I over sprayed too much. That way I was still being productive. After doing that I would measure what I had left in the tank and work it from there. I typically spray a dosage that is under what the label recommends. That way I know I won't mess up the application. I have since increased the dosage slowly so that I don't have any issues.

So my main point is that, if your in doubt ? spray less then is recommended and work it up slowly from there from application to application. At some point you'll know exactly how fast your pace is and how much materiel you need.

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