Calibrating a Spray Rig

Calibration is very important when it comes to applying chemical to your golf course. Using the new chemicals with very low use rates makes each droplet that comes out of your nozzle count that much more. Only a small percentage of solution is active ingredient. I make sure that we check our calibration each time we spray. I will explain how we keep our spray rig accurate for every spray.


Some math is required to calibrate your spray rig. I make sure I have all the tools ready when calibrating. An easy to read measuring cup that will hold two quarts, an accurate stop watch and a measuring wheel or tape that will go over 100 ft.

The first step is to get the fixed measurements of your rig. Effective spray width is a good starting point. This is not necessarily the entire boom width. When a nozzle is placed on the boom it has overlap with the next nozzle. My spray rig is set up for nozzle-to-nozzle overlap. When I measure effective spray width I measure from nozzle to nozzle on each end of the boom(18ft). The pattern that goes the extra ten inches from that nozzle is not a full rate, thus not effective.

Our second fixed rate is the speed of the vehicle. First you need to set a distance that you will travel. I measure 100 feet on flat turf covered ground. Traveling on turf is important since asphalt or concrete has little resistance. The farther you measure the more accurate your calculation. I use my stopwatch to record the time it takes for the spray rig that is carrying 50% capacity with the pump on. With my spray rig I use second gear low and fill the tank with 100 gallons (200 gallon capacity). The importance of the water in the tank and the pump running gives the cart an average load that it might be under while trying to travel across a fairway or green. The accelerator must be fixed. A stop should be installed if needed so each time the pedal is pushed it depresses to a consistent position.

Now that you have the fixed measurements you can begin the calibration process. We know the effective spray width (my rig 18ft). We know how long it takes to travel a specific distance (100ft, 17 sec.). With those numbers we can see how many square feet we can cover in a given time (1800 sqft, 17sec.). So now I want to make sure I am not losing anyone with the numbers. 18ft = effective spray width, 17 seconds to travel 100ft and 18ft by 100ft = square footage covered.

So now we know what are spray rig can cover we need to find out how many gallons per acre we will use. This is where we need to measure the output from the nozzles. I have three sections and choose one nozzle from each section to collect from and check consistency. You can check every nozzle if you suspect your nozzles are getting old. Adjustment of the pressure to the nozzles will also adjust output. I just make sure I am within the specifications of the particular nozzle for pressure.

If you have multiple nozzles for the type of product you are using then select the nozzle you want to use. Once they are in place I make sure the throttle is consistent with the earlier measurement and the pump is primed. Turn on all nozzles and check to make sure nothing is malfunctioning. One plugged nozzle can throw off your pressure and affect your output. Once you have looked over your setup you can pick one nozzle from each section and begin your collection. I collect 17 seconds from each nozzle noting the output. Once you have these numbers, which should match each other to a fraction of an ounce, you are ready to calculate your overall output.

So in my case I measured 24 ounces for each nozzle. I have a total of 11 nozzles so my total output for all the nozzles in 17 seconds is: 264 ounces. I convert this number into gallons: 2.0625 gal. This is the volume that we are putting out over 1800 square feet. We know this from our earlier measurements. So now you need to take the 2.0625 gallons per 1800 sqft. and convert it to gallons per acre. I take 2.0625 and divide by 1.8 to make it gallons per 1000 sqft.: 1.145833333 gal/1000sqft. Multiply 1.145833333 gal by 43.56 (1000sqft in an acre): 50 gallons per acre. So with this number I know I have 200 gall capacity and I can cover 4 acres with one tank.

Now you know the exact output of your spray rig. Simple right? The math can become a little confusing but if you practice it enough it will get easier with the conversions. So now with your knowledge of your spray rig’s output you can calculate the amount of chemical and water you need to add to cover any given area. If you have any questions and need to talk to a human, I can walk you through the process fairly easily. Send me an email and I will get back to you on the phone at my earliest convenience.