Today we are going to talk about calibration and application of liquids to get the most accurate, consistent and efficient results. Most of our R&D at VSI comes from actually field testing our equipment in our commercial snow and ice division where we have been using almost exclusively liquids (no granular product) since 2010!
One of the best parts about liquids is the precision and accuracy they can be applied with across all truck sizes and operator experience levels. This is because liquids are much easier and more consistent to track, meter and calibrate around than granular products are. Liquid is a very consistent medium where bulk granular de-icing products are not due to variance in gradation (granule size), moisture content, temperature and compaction rate in the spreader. All of these factors will affect application rate even if your spreader settings remain consistent.
Experienced operators can sometimes adjust for these variables, but experienced operators are not easy to come by and we all know that banking your quality control, margins and efficiency on any individual employee is risky. A system is best, and using liquids allows you a very simple and consistent system to accurate application.
A calibrated liquid spray system can lower operator inexperience risk of over or under application of product by as much as 90%. 4 years ago, in our snow and ice operation, we ran 5 de-icing trucks with automatic speed rate control and 1 deicing truck with manual calibration (on/off only). The results over one average Minnesota winter were eye opening!
Over application of product for the course of the season was almost 30%. Maybe it doesn’t sound like much.. But what if all 6 spray trucks over applied by 30%? For us, 4 years ago, that would have meant an extra 60,000 gallons of brine and additive would have been wasted over the course of the season, not to mention the unnecessary environmental impact, wasted labor hours, refill time and so forth, the cost of which would have paid for the 6 spray units to have automatic rate control 3 times over…
The easiest and best way to achieve automatic speed rate control is to use a system like all of our units 305 gallons or larger come standard with. This unit uses a GPS speed control puck, a magnetic flow meter (which measures the flow rate passing through the system) and a proportioning valve that actually meters and adjusts the flow rate of the liquid to match your speed. The controller with built in programming for rate control acts as the brains of this operation.
In these systems you input key data and it does the rest. On VSI liquid de-icing sprayers, you simply supply your desired gallons per acre rate and click which boom sections you want to spray from, and it does the rest in real time. As you accelerate the proportioning valve opens further to allow additional flow to the boom to match your speed. So if your desired application rate is 40 gallons per acre, it is going to adjust your flow rate up or down as your speed increases or decreases to apply that consistent 40 gallons per acre regardless of your speed of travel, or fluctuations in it.
How does this work? It's a simple mathematical equation inside of the control unit. The control unit knows how wide each boom section is, the GPS speed sensor sends a signal telling the control unit how fast the truck is traveling, and you have already told the system how many gallons per acre you want to apply, so now Gallons per acre= speed x flow rate (GPM) x spray width. The system automatically adjusts the flow rate to match the desired application rate with the current speed in real time. Come to an abrupt stop, the system quickly closes the proportioning valve and boom section valves to stop flow. Accelerate quickly and the boom section valves re-open and the proportioning valve rapidly re-opens to provide the correct flow rate for the given GPA target and real time speed.
Some important things to keep in mind with automatic rate control systems is that your boom must be balanced (at a given pressure range, the middle and side booms are applying a consistent amount of product per acre). We often see spray booms that are putting out a high flow rate in the middle boom section and just have a single or dual side nozzle that covers 5-10’ off each side but does not put out requisite volume to match your center boom. This sort of defeats the purpose of automatic rate control..
Another thing to consider with automatic rate control systems is that If you are using a turbine flow meter or pulse width modulation system (for electric/hydraulic), you need to adjust for the specific gravity (density) of what you are applying. Straight salt brine and an 80/20 blend of brine and additive have substantially different density and thus will apply differently if the change in specific gravity is not adjusted for. The nice part about a magnetic flow meter like the ones on VSI spray units is that they automatically adjust for changes in specific gravity. Again, it's not a major percentage of over/under application with turbine flow meters or PWM systems that have not been adjusted for differences in specific gravity, but over the course of a season and multiple spray units, it does add up and make a difference!
-To reduce or eliminate product waste. Brine is inexpensive, but when you start putting in additives and factor in the extra labor/truck expenses associated with extra hours and miles caused by refilling more often than necessary due to over application or due to return trips/call backs due to under application, its a no brainer. Efficiency gained by proper calibration will help save on material waste, but efficiency of labor is also incredibly important!
-Protecting the environment. Liquids are a great step forward, so why not apply them at the correct rates while you are at it?
-Consistency between operators. Don't need your “A” team to do a great and consistent job
-Effectiveness of application. Get the results you and your customers EXPECT