As the spraying season recedes in the rear-view mirror, it’s a good time to think about how the season went and what the most memorable moments were for you. Did you have a drift issue? A tank clean-out mistake? Did your products work as expected, and if not, do you know why? Did you lose too much time getting the sprayer filled, or unplugging nozzles?

Noting these events might give you an idea what to research over the trade show season, and what you might be able to change for next year. Some of our biggest struggles in spraying involve the start and end of each spray day. These are prime candidates for improvement.

At the end of a spray day, we should ideally clean the sprayer. During that process, we may struggle with where to put the waste product, including large rinsate amounts, and of course, the uncertainty of whether the job is actually done (since clean water looks exactly the same as contaminated water).

If we’re not prepared to clean the entire sprayer plumbing, we should at least rinse the boom with water. This can prevent future problems, especially with products formulated as suspensions or emulsifiable concentrates which can settle and cling to various sprayer parts.

When starting a new field after the sprayer is cleaned and the boom has water in it, we need to prime the boom. Air purge is very useful in those instances. But without air, the question is how long to purge for, and where best to do this (pro tip at bottom of article).

These straightforward tasks are complicated by the increasingly convoluted plumbing featured on modern sprayers. Ask someone to explain their sprayer’s plumbing system to you one day. It’s a long story! Better engineered systems would be welcome.

Fortunately, virtually any sprayer can be modified to suit your needs. Let’s talk about a few ideas for a winter project:

1.      Boom flush. It’s good practice to flush clean water through your boom at the end of spraying even if the main tank remains full of product. Some sprayers have an air purge system to eliminate liquid from the plumbing and that is a great feature. A water flush should follow that purge so that any residual pesticide is diluted and removed before it can dry on and become hard to remove later. First you’ll need a clean water tank on the sprayer (150 gallons is enough). Second, plumb a feed so that this clean tank can be the sole source of the water supplied to the solution pump. Select this source, shut return lines down or off, and pump clean water through boom. Idling the engine to avoid pressure spikes may be necessary. Sprayers that have an auto-rinse cycle will likely be able to draw clean water, but may not be able to push it to the boom, directing it to the wash-down nozzles instead. Check to see what's possible, and make the changes you need.

2.      Clean water pump. Installing a second pump dedicated to the clean water tank has several advantages. We’ve talked about “continuous rinsing” before on as a way to dilute the tank remainder faster. The idea is to speed up and improve the quality of rinsing the system.

Continuous rinsing starts by spraying the product tank completely empty in the field, possibly by returning over a previously sprayed swath at a lower application rate. Once the tank is empty and spray pressure drops, turn on the second pump, keeping agitation and purge lines open. This pump now delivers clean water to the tank via the wash-down nozzles. The solution pump soon regains pressure, and delivers the rinsate to the boom and the return lines.

The key to this system is to closely match the wash-down pump volume to the application rate. If the sprayer is delivering 20 gpm to the boom, the wash-down nozzle should be close to that. Under-delivering with the wash down is better than over-delivering, because the latter allows spray rinsate to accumulate in the tank, making dilution less effective.




The wash-down nozzles have to be able to handle the incoming water rate and still function as intended. This will likely require some observation and tweaking.

When the clean water tank is empty a few minutes later, the main tank will be rinsed and the rinsate in the return lines and boom will be very dilute, more dilute than even a triple rinse would have achieved. And the whole process didn’t require any stopping and dismounting of the sprayer.

Additionally, give this pump the option to deliver water just to the boom without using the wash-down nozzles. Now it can be used to rinse water through the boom.

Continuous rinsing is just one of the steps in sprayer clean out. Cleaning strainers, boom ends and other sprayer parts are just as important.

3.      Boom ends. We’ve mentioned this part of the boom many times. Boom ends that extend beyond the last nozzle on each end of a section must be flushed regularly to get rid of product and debris that gets stuck there. Many producers install ball valves to achieve this, but must do so regularly. A simpler way is to use the Express Nozzle Body End Caps from Hypro. These bleed air continuously, and also prevent accumulation of dead-end contamination. They do need to be flushed, and this can be done by pulling a plug or rotating the turret to an open (no nozzle) position.

4.      Recirculating boom. This is a significant change, but worth considering. Conventional plumbed booms are separated into five to 13 sections. Each has two ends at which the spray stops and where air and contamination can accumulate (see point #3). Each section feed has a shut-off valve, controlled via the rate controller. Once the spray mixture leaves the pump and bypass valve, it is committed to leaving the sprayer.  

In a recirculating boom, the boom is a single section and its entire volume can become a part of the tank. In other words, the liquid can return to the tank if desired. Spray is pressurized and fed to one or both ends of the boom. Valve positions determine its flow, either forcing it out through the open nozzles, or returning it to the tank. Sectional control is achieved with individual nozzle shut off, either using air or electric solenoids.

1.      Three advantages:
(a) the boom can be primed with new product without spraying. The surplus goes back to the tank.
(b) the boom can be flushed with water without spraying while material is still in tank, and without spilling anything on the ground. Again, the surplus goes back to the tank.
(c) high-resolution sectional control with individual nozzle shut off is a byproduct of this design. Fast response, high res, saves money.

This design does have some challenges. In designs where the boom is fed just from one end, a significant volume of spray mix is returned to the tank for dilution. Designs where the boom can be pressurized on both ends address this issue.

5.      Steel lines. Steel cleans easier than plastic, and this material makes a lot of sense for booms. But it also makes sense for the boom feeds, currently handled by black rubber hose. This hose is a literal black box. We can’t see inside it, and we don’t know if and where potential contamination resides. It has considerable surface area. Consider replacing portions of your feed lines with steel. The boom is the obvious candidate. Aside from easier clean out, it also helps with faster nozzle shut off because it doesn’t expand with pressure.

A word about dumping the tank remainder on the ground. It’s a bad practice for many reasons. Let’s examine just one of those. When you spray a product at 10 gpa, you actually cover each square metre with about 10 ml of spray mix. When you flush your boom ends on the ground, you’re probably dropping two or three gallons in the same area. That’s 1,000 times the label rate at each boom end, 10 to 26 times per boom. If you dump your tank remainder and all the hoses, say 20 or 30 gallons, that’s 10,000 times the label rate if it covers one square metre. That’s leaching, run-off, residual potential, and not a good story.

Many of the changes outlined above help prevent that from being necessary.

Pro Tip: To find out how much water your plumbing (from the pump to the boom ends) holds, do this: After cleaning with water (and without an air purge) use an EC formulation as a marker. ECs have a white milky appearance (some crop oils are ECs). Reset your sprayed gallons on your rate controller. Start spraying and watch for the last nozzle on your furthest and longest section to spray white. Stop spraying and check your sprayed gallons. That’s your volume. No matter the size of nozzle or application volume, it stays constant. To be sure the boom is primed with a new mix, spray until those gallons are reached and you’re set.



Tom Wolf, Ph.D, P.Ag.
Tom Wolf grew up on a grain farm in southern Manitoba. He obtained his BSA and M.Sc. (Plant Science) at the University of Manitoba and his Ph.D. (Agronomy) at the Ohio State University. Tom was a research scientist with Agriculture & Agri-Food Canada for 17 years before forming AgriMetrix, an agricultural research company that he now operates in Saskatoon. He specializes in spray drift, pesticide efficacy, and sprayer tank cleanout, and conducts research and training on these topics throughout Canada. Tom sits on the Board of the Saskatchewan Soil Conservation Association, is an active member of the American Society of Agricultural and Biological Engineers and is a member and past president of the Canadian Weed Science Society. Twitter: @nozzle_guy

Last issue, we introduced the concept of Pulse Width Modulation (PWM), described how it works, and identified the main commercial systems available in North America. This issue will contain practical information on how PWM can be implemented on a sprayer on your farm.

What can PWM do?

With conventional pressure control, spray quality and pattern width vary with travel speed. Left to right: 30 psi, 40 psi, 50 psi, 60 psi
With conventional pressure control, spray quality and pattern width vary with travel speed. Left to right: 30 psi, 40 psi, 50 psi, 60 psi

Spray Quality: Since PWM systems can alter flow rate without affecting spray pressure, the user can select a spray pressure that meets their spray quality goals and expect this spray quality to remain constant throughout the field, regardless of travel speed.

Spray Drift Control: Although PWM does not by itself have any unique capabilities to reduce spray drift, it does make spray drift management easier. For example, the most accessible tool for reducing spray drift is to increase droplet size by reducing spray pressure. In a conventional system, the reduction of spray pressure can only be achieved with a reduction in travel speed because the lower spray pressure also reduces the overall flow rate. With PWM, the loss of flow with a reduction in spray pressure can be compensated by an increase in duty cycle (DC). As a result, lower pressures do not require a reduction in travel speed provided there is sufficient DC capacity in the system. Also, PWM systems use larger orifice nozzles, which naturally produce larger droplets.

Tom Wolf, Ph.D, P.Ag.
Tom Wolf grew up on a grain farm in southern Manitoba. He obtained his BSA and M.Sc. (Plant Science) at the University of Manitoba and his Ph.D. (Agronomy) at the Ohio State University. Tom was a research scientist with Agriculture & Agri-Food Canada for 17 years before forming AgriMetrix, an agricultural research company that he now operates in Saskatoon. He specializes in spray drift, pesticide efficacy, and sprayer tank cleanout, and conducts research and training on these topics throughout Canada. Tom sits on the Board of the Saskatchewan Soil Conservation Association, is an active member of the American Society of Agricultural and Biological Engineers and is a member and past president of the Canadian Weed Science Society. Twitter: @nozzle_guy

This is the first in a series of the best articles available on, edited under agreement for FARMING FOR TOMORROW to provide special emphasis on Western Canadian agronomic conditions.

There’s been a lot of talk about rate control in spraying, and one key technology is pulse width modulated spray systems (PWM). Although PWM has been commercially available for a number of years, we are seeing new products enter the market. This article explains what PWM is and how to make it work in a spray operation.

Rate Control Primer

All sprayers experience fluctuations in travel speed. Operators speed up or slow down as conditions demand. In order to maintain a constant application volume per acre, the spray liquid flow must change in direct proportion to travel speed. The sprayer achieves this with a rate controller.

The rate controller uses four pieces of information to ensure a constant application rate.

  • The user enters the width of the boom and the desired water application rate.
  • The sprayer provides travel speed information and liquid flow rate.

Using a simple mathematical formula, the rate controller calculates what the required liquid flow needs to be for any given travel speed, and changes the flow by adjusting the pump pressure. The sprayer operator keeps an eye on the spray pressure to ensure it doesn’t exceed the capabilities of either the nozzle, the plumbing, or the pump or that it does not produce an undesirable droplet size or spray pattern.

Capstan solenoid b)

Pulse Width Modulation utilizes conventional plumbing: a single boom line and a single nozzle at each location. Liquid flow rate through each nozzle is managed via an intermittent, brief shutoff of the nozzle by an electric solenoid that replaces the spring-loaded check valve. Typical systems pulse at 10 Hz (the solenoid shuts off the nozzle 10 times per second). The duration of the nozzle in the “on” position is called the duty cycle (DC) or pulse width. 100 per cent DC means the nozzle is fully on, and 20 per cent DC means the solenoid is open only 20 per cent of the time, resulting in the nozzle flowing at approximately 20 per cent of its capacity. The ability to control the duty cycle is referred to as pulse width modulation.

Pros and Cons

There are two chief features of a pressure-based approach that affect the spray operation.

  • Pressure affects spray quality and spray patterns. Higher pressures (the result of faster travel speeds) result in finer, more drift-prone sprays, and lower pressures may, in addition to producing a coarser spray, reduce the spray’s fan angle. The resulting narrow patterns can result in less overlap and poor pattern uniformity.
  • Pressure is not very effective at changing flow rates. Increasing the travel speed by a factor of 2 requires a pressure change of four-fold, as predicted by the square-root relationship between flow rate and pressure. As a result, a system capable of pressures ranging from a low of 30 psi to a high of 90 psi (a three-fold change in pressure) results in only a 1.73-fold change in flow rate (and travel speed). 1.73 is the square root of 3.

In comparison, PWM systems do not rely on pressure to effect new flow rates. Instead, the duty cycle of the system affects nozzle throughput. Boom spray pressure stays constant throughout the duty cycle range, and as a result, so does spray quality and spray fan pattern angle. In practice, the lowest duty cycles increase droplet size, and reduce fan angle, somewhat. The operator also has the option of adjusting the spray pressure to get a desired droplet size, even “on the fly” and the PWM system will maintain the desired application rate.

A PWM system can therefore change travel speeds by about a factor of five (from 20 to 100 per cent DC). Duty cycles less than 20 per cent, although possible, are not recommended.

Note that the actual measured change in flow rate achieved by a PWM system is not directly related to duty cycle. The actual nozzle flow rate is greater than that predicted by a duty cycle calculation, especially for smaller nozzles.

Commercial PWM Systems

AIM Command
AIM Command

Capstan: Capstan Ag Systems was first to offer a PWM system, the Capstan Synchro. The Capstan product was later licensed to Case IH sprayers and named AIM Command. It was a factory option on Case sprayers from 1998 to 2016, manufactured by Capstan. The system featured a separate monitor, permitted PWM to range from 100 down to 15 per cent, and featured an alternating pulse in which every second nozzle pulses identically, and alternating nozzles work in a 180 degree offset. In other words, in a system operating at 50 per cent DC, when any given nozzle is on, adjacent nozzles are off. This results in a “blended pulse” that minimizes the likelihood of skips.

Sharpshooter Monitor

In recent years, Capstan has entered the retrofit marketplace and the technology has been installed on many brands of sprayers at the dealer level. The hardware is identical to Case products, with some minor differences in how the software interacts with the rate controller.

Since 2012, Case has offered an enhanced version called AIM Command Pro (Capstan calls their version Pinpoint). This system offers individual nozzle sectional control as well as turn compensation. In addition, the enhanced system offers individual nozzle diagnostics that provides operational details to the sprayer operator.

Raven Hawkeye

Raven: In 2014, Raven introduced a system called the Hawkeye. The system uses an ISOBUS approach that works with the Viper 4 monitor. The electric solenoids are similar to those on the Capstan systems. The basic system (Hawkeye) features turn-compensation, but not individual nozzle sectional control. Section resolution is determined by the limits of the monitor, for example, 16 sections on the Raven Viper 4. Hawkeye 2.0 HD, announced December 2015, allows for individual nozzle on-off control. Hawkeye will be available as a factory option on New Holland, Apache, and Case sprayers starting in 2017.

John Deere ExactApply nozzle

John Deere: John Deere announced their PWM version on August 29, 2016. Called ExactApply, the system features 30 Hz PWM, individual nozzle control, automatic and manual nozzle switching, turn compensation, programmable rates by nozzle, nozzle plug detection, and LED lighting. It is expected to be competitively priced compared to the other systems, and offers higher maximum flow rates through its solenoid (up to 50 US gpa at 15 mph).

Two nozzles can be sprayed simultaneously at each nozzle location, and one or the other, or both, can be selected from the cab to extend flow rate ranges or to select a different spray quality. Units are expected to be tested on sprayers in 2017, and become available as a factory option or a retrofit in 2018.


TeeJet: TeeJet has a system called the DynaJet Flex 7120 that uses either a monitor or Android tablet to display pressure, duty cycle, and droplet size. DynaJet is available to OEMs and to the aftermarket. The unique aspect of the TeeJet system is the ability to dynamically select different droplet sizes, and the system will maintain that droplet size across a wide range of speeds or application rates. The TeeJet system is compatible with any flow-based rate control system, and does not require a TeeJet spray control. The product is available from TeeJet dealers.

Next Issue: Pulse Width Modulation, Part 2: How to make PWM work for you.