Case Study: Boom Sprayer Nozzles on a 24 m Row-Crop Sprayer

A 24 m boom lays a 24 m wide strip of spray on every pass. Driven at 12 km/h it sweeps a theoretical 28.8 ha an hour, about 23 ha an hour once turns and refills are counted. Every litre that leaves a tip lands on the target, drifts past the boom edge, or evaporates on the way down.

This case covers a European row-crop operation of 1,200 ha that ran a 24 m boom sprayer on plain flat fan tips. The retrofit replaced them with air induction nozzles and added per-nozzle PWM section control. The figures are working values for a sprayer of this class, not for one machine.

Case Snapshot

The reference configuration below is the generic shape of the installation.

Item	Reference configuration
Industry	Arable row-crop farming, 1,200 ha of cereals, oilseed rape, and maize
Duty	Broadcast herbicide, fungicide, and insecticide, three passes a year
Equipment	Trailed 24 m boom sprayer, 4,000 L tank, 48 nozzle positions at 0.50 m spacing
Original setup	Standard flat fan tips, ISO 10625 size 04, four fixed 6 m sections, 2.6 bar rail
Nozzle chosen	Air induction twin flat fan, ISO 10625 size 04, 110 degree pattern, twin turret body
Operating point	150 L/ha at 12 km/h, 1.5 L/min per nozzle, 72 L/min across the boom, 3.0 bar, PWM duty 94 percent
Material requirement	Hardened stainless tip insert, polyacetal body, EPDM seals, twin turret for product switching
Compliance	ISO 10625 tip colour code, ASABE S572.1 droplet class, EN ISO 16122 inspection, local label rules

The shape repeats on any sprayer from 18 to 36 m running a three-pass arable program. Mounted, trailed, and self-propelled machines use the same tip sizing.

The Challenge

The farm cropped 1,200 ha in blocks of 8 to 40 ha, hedged on most sides, with a river boundary and houses along two edges. The program was three broadcast passes a year: a pre-emergence residual, a post-emergence contact herbicide, and a fungicide plus insecticide pass. That is 3,600 treated hectares a season.

The boom carried 48 tips at 0.50 m spacing, ISO 10625 size 04 flat fans rated 1.6 L/min at 3.0 bar, run at 2.6 bar to land 150 L/ha at 12 km/h. A plain flat fan at that pressure makes a Medium spray under ASABE S572.1, with a VMD near 280 µm.

Drift was the first cost. Wind above 3.5 m/s stopped the job, and local records showed that window closed on about a third of otherwise workable days. The season finished on 62 spray days against a need for about 72.

Overlap was the second cost. The boom had four fixed 6 m sections and no turn compensation. Headlands, point rows around the hedges, and every turn took two or three passes at full rate, which added about 12 percent to the volume applied across the season.

The third cost was the wrong droplet size for the target. A Medium spray at 2.6 bar throws a wide band of fines that travel with the wind, and the drops that land are small enough to shatter on a waxy leaf.

Tip wear was the fourth. The sprayer covered 3,600 treated hectares a season and a set of tips reached plus 10 percent flow in about 400 hours. The operation kept no tip flow record, and off-target incidents ran at four a season.

The Solution

The operation fixed four things together: droplet spectrum, boom height, section control, and calibration discipline. Changing only the tip would have cut drift and cost spray coverage.

The tip moved to an air induction twin flat fan, ISO 10625 size 04, a 110 degree pattern rated 1.6 L/min at 3.0 bar. An air induction nozzle draws air into the liquid stream inside the tip, so the drop leaves with an internal bubble that bursts on impact. The twin fan puts spray on both faces of a vertical leaf instead of one.

The rail now runs at 3.0 bar for a stable coarse pattern. At 12 km/h, 1.6 L/min per nozzle would be 160 L/ha, so PWM trims the duty to 94 percent to land 150 L/ha. Rate is set by duty cycle and not by dropping pressure into a range where the pattern breaks up.

Boom height fell from 0.75 m to 0.50 m, which narrows each fan and raises the deposit in the overlap band.

Each tip now sits on its own solenoid valve driven at 10 Hz, and the GPS switches individual tips, so the effective section width went from 6 m to 0.50 m. On a turn, turn compensation raises duty on the outer tips and lowers it on the inside.

Calibration is the last step, with one nozzle per section collected at working pressure and checked against 1.6 L/min. A twin turret on every position carries a finer conventional tip for the contact pass, because not every product suits a coarse spray. The same coverage decision runs through the herbicide nozzle selection guide.

The Engineering Detail

Area rate: 24 m at 12 km/h and 184 ha a day

Area rate is width times speed, carried through with units. A 24 m boom at 12 km/h travels 12,000 m/h, so it sweeps 24 x 12,000 = 288,000 m²/h, which is 28.8 ha/h. At a field efficiency of 80 percent for turns, refills, and headlands that becomes 23.0 ha/h, so one 8 hour day covers 184 ha and one pass of the farm takes 6.5 days.

A 4,000 L tank at 150 L/ha holds 26.7 ha, which is 6.9 refills a day, and that fill time is most of the 20 percent efficiency loss.

Step	Value	Arithmetic
Boom width	24 m	48 nozzles x 0.50 m spacing
Speed	12 km/h	200 m per minute
Nominal rate	150 L/ha	label dose and nozzle chart
Boom flow	72 L/min	150 x 12 x 24 / 600
Flow per nozzle	1.5 L/min	72 / 48
Tip rating	1.6 L/min	ISO 10625 size 04 at 3.0 bar
PWM duty at the reference point	94 percent	1.5 / 1.6
Area rate, theoretical	28.8 ha/h	24 x 12,000 / 10,000
Area rate, effective	23.0 ha/h	28.8 x 0.80
Day rate	184 ha	23.0 x 8 h
Tank area	26.7 ha	4,000 L / 150 L per ha

The two routes agree. A boom flow of 72 L/min is 4,320 L/h, and 4,320 / 150 = 28.8 ha/h, the same figure that width and speed gave.

Flow per nozzle: 1.5 L/min and 72 L/min across the boom

The working formula for a boom sprayer is Q in litres per minute equals litres per hectare times speed in km/h times width in metres, divided by 600. The 600 is the unit conversion that turns hectares, kilometres, and hours into minutes.

For the whole boom, 150 x 12 x 24 / 600 = 72 L/min. For one nozzle the width is the 0.50 m spacing, so 150 x 12 x 0.50 / 600 = 1.5 L/min. With 48 nozzles, 48 x 1.5 = 72 L/min.

Tip size follows from that. Under ISO 10625 a size 04 tip flows 1.6 L/min at 3.0 bar, so 1.5 L/min is 94 percent of rated. The K-factor form links flow and pressure, Q = K x square root of P, which gives K = 1.6 / square root of 3.0 = 0.92 L/min per bar to the power 0.5. At 2.6 bar the same size 04 flowed 0.92 x square root of 2.6 = 1.49 L/min, which is why the pre-retrofit rate was also near 150 L/ha.

Flow rises with the square root of pressure, never in proportion. Doubling the flow needs four times the pressure, so pressure is the wrong lever for rate control on a boom of this width. That is the reason PWM exists.

Droplet spectrum: ASABE S572.1 and the ISO 10625 colour code

Two independent schemes describe a spray tip, and mixing them up is a common error. The tip colour codes the flow rate. The droplet class codes the spray quality, and it moves with pressure.

Under ISO 10625 the colour is set by flow at 3.0 bar. Size 015 is traffic green at 0.6 L/min, 02 is zinc yellow at 0.8, 025 is signal violet at 1.0, 03 is gentian blue at 1.2, 035 is purple red at 1.4, and 04 is flame red at 1.6. The colour says nothing about droplet size.

Droplet class is separate. ASABE S572.1 sorts a spectrum by volume median diameter, the size that splits the spray volume in half. This farm moved from the Medium band to the Coarse and Very Coarse bands, and the fines fraction is what actually drives drift.

Class, ASABE S572.1	VMD range	Role in this program
Fine	106 to 235 µm	contact herbicide on small weeds
Medium	236 to 340 µm	the old flat fan at 2.6 bar, VMD near 280 µm
Coarse	341 to 403 µm	the air induction tip at 3.0 bar, VMD near 380 µm
Very Coarse	404 to 502 µm	the same tip at 2.5 bar, VMD near 430 µm
Extremely Coarse	503 to 665 µm	soil applied residuals and liquid fertiliser

VMD alone is not the drift number. A spray can hold a Coarse VMD and still carry a tail of drops under 150 µm, and those drops are the ones that leave the field. Volume below 150 µm fell from about 20 percent to about 4 percent here, which matters more than the VMD.

Drift, the 150 µm fines line, and a 5.5 m/s wind window

Drift loss past the boom edge is a fraction of the applied volume, and it scales with the fines fraction and with wind speed. At 3.5 m/s the old Medium spray lost roughly 12 percent of its volume beyond the sprayed strip. The air induction tip at the same boom setting lost about 4 percent, and most of that came off the outer nozzles.

That gap changes the working window. The operation set its practical limit at 3.5 m/s with the old tips and at 5.5 m/s with the new ones. On the local wind record that turned 62 suitable days into 74, twelve extra on a program that needs about 72.

Twelve days is worth more than it looks, because a missed pre-emergence window is a lost pass, not a delayed one. A coarse class also shrinks the buffer zone, which recovered the river boundary strips that used to be hand treated. The general version of that decision sits in the agricultural spraying notes.

Spray coverage: 24 drops per square centimetre

Coarse drops cut drift and they also cut the number of drops on the leaf. Volume is fixed by the rate, so at one volume a 280 µm spray carries far more drops than a 400 µm spray, by the ratio of the diameters cubed.

Drops per square centimetre governs a contact herbicide, because the active has to touch the leaf where the drop lands. A systemic product moves inside the plant and tolerates fewer, larger drops. The farm measured both settings on water sensitive paper pinned at the boom centre and at the boom edge.

At 150 L/ha the Medium spray left about 70 drops/cm² and the air induction tip left about 24, a ratio near 2.9 that matches (400 / 280) cubed. Coverage held at 24 drops/cm² stays above the 20 drops/cm² floor for the systemic products and well short for the contact herbicide.

Two changes put the count back where it had to be. Boom height fell from 0.75 m to 0.50 m, and the contact pass moved to 180 L/ha at 10 km/h on the finer tip in the turret, which brings the count to about 35 drops/cm².

The geometry is simple arithmetic. Covered width = 2 x standoff x tan(angle / 2). A 110 degree fan at 0.50 m covers 2 x 0.50 x tan 55 = 1.43 m against a 0.50 m spacing, so each point on the ground sits under 2.9 fan widths.

Boom height	Covered width, 110 degree fan	Fan widths over a 0.50 m spacing	Relative deposit in the band
0.75 m	2.14 m	4.3	0.67
0.60 m	1.71 m	3.4	0.84
0.50 m	1.43 m	2.9	1.00
0.40 m	1.14 m	2.3	1.25

Lowering the boom raises the deposit by about half, at the cost of a narrower band and a tighter tolerance on boom ride. Below about 0.40 m the coarse drops shatter and bounce off the leaf, so 0.50 m is the floor for this class.

PWM at 10 Hz: duty, bypass, and the overlap count

PWM holds rate by switching the tip on and off. At 10 Hz the valve cycles ten times a second, and the duty cycle is the fraction of each 100 ms period that it stays open. Flow is close to linear in duty, Q average = Q rated x duty, within plus or minus 3 percent between 20 and 100 percent duty.

At the reference point the duty is 94 percent, so the valve is open 94 ms and shut 6 ms. Dropping to 8 km/h at the same rate needs a lower flow per nozzle, and the duty follows it down without a pressure change. That turndown holds rate across the 8 to 16 km/h range instead of swapping tips at the headland.

The bypass keeps the pattern stable. Closing a section removes its nozzles from the flow, and the pump keeps delivering unless the surplus has a route. If the rail climbed from 3.0 to 6.0 bar, the remaining tips would flow square root of 2 times rated, or 41 percent over. The regulating valve returns the surplus and holds the rail inside plus or minus 0.2 bar.

Overlap falls straight out of the smaller section. With four fixed 6 m sections, a point row or an angled headland took three passes over part of its width. With one-tip sections and turn compensation, that same ground takes one. The overlap penalty fell from about 12 percent of the applied volume to about 3 percent, and that is the source of the product saving below.

Frequency has a floor. At 10 Hz the shortest off time in the working range is a few milliseconds, long enough for the coarse pattern to re-form after each pulse. At 5 Hz the off time passes 100 ms, rail pressure swings with the valve, and water sensitive paper shows banding. At 20 Hz a low duty pulse is only a few milliseconds wide, so linearity suffers at the low end of the duty range.

Calibration at 5 percent, wear at 10 percent, and 50 mesh filtration

A coarse tip still has to pass a flow check, and the collect method is the only figure that matters: one nozzle per section, a graduated cylinder, 60 seconds at working pressure, against 1.6 L/min. This farm accepts plus or minus 5 percent on a new tip and puts anything above plus 5 percent into a wear set.

The wear threshold is 10 percent. A tip at plus 10 percent over-applies by 10 percent on that section, and at about 52 dollars a hectare a worn set on one quarter of the boom lifts the season bill by about 2.5 percent with no visible sign in the field.

Filtration follows the orifice, to about one third of the smallest passage. An air induction 04 tip has a metering orifice near 1.4 mm, which sets a floor near 450 µm, so the farm runs a 50 mesh line strainer at 300 µm plus a 100 mesh element at the boom inlet. A 100 mesh screen alone blinds within days on a suspension formulation.

A partly blocked tip at the far end of a 24 m boom under-applies while the near sections stay correct, so rail pressure is logged at the boom inlet and not at the pump. Three failure modes belong on the setting sheet. A spectrum too coarse for the product leaves too few drops, the weed survives a sub-lethal dose, and repeated sub-lethal exposure selects for resistance. PWM below its frequency floor pulses the boom and bands the deposit. A worn air induction tip both over-applies and loses part of its drift advantage, because the extra flow comes from a changed internal geometry.

The Results

The numbers below compare the season before the change with the season after, at the same 3,600 treated hectares and the same program.

Metric	Before the retrofit	After the retrofit	Unit
Tip	Standard flat fan 110-04	Air induction twin fan 110-04
Rail pressure	2.6	3.0	bar
Spray quality, ASABE S572.1	Medium	Coarse to Very Coarse
VMD	280	400	µm
Volume below 150 µm	20	4	percent
Drift loss past the boom edge	12	4	percent of applied
Working wind limit	3.5	5.5	m/s
Suitable spray days per season	62	74	days
Field-average application rate	168	154	L/ha
Spray volume per season	604,800	554,400	L
Product spend per season	209,700	192,800	dollars at 52 per ha
Coverage on water sensitive paper	70	24	drops per cm²
Boom height	0.75	0.50	m
Off-target complaints	4	0	per season

Product was the largest saving. Field-average rate fell from 168 to 154 L/ha, which is 8 percent, and the season bill fell by the same share because the concentration did not change. The 604,800 L figure is 3,600 ha at 168 L/ha, and 554,400 L is the same area at 154 L/ha, both field-average rates including overlap.

The drift figures did more work than the volume. Volume below 150 µm fell from 20 to 4 percent and off-target loss from about 12 to about 4 percent of applied liquid.

The window was the second gain. Twelve extra days lifted available days from 62 to 74 and removed the two late passes that had been squeezed into marginal conditions the previous season.

Coverage was the one figure that fell, from 70 to 24 drops/cm² at the reference rate. It stayed above the threshold for the systemic products and had to be bought back for the contact pass with a finer tip, a slower pass, and a lower boom. Tips now carry a flow record that catches plus 10 percent inside one season, and the four off-target complaints went to zero. The tip family used here is listed on the agricultural spray nozzle page.

Why This Matters

Most upgrades on a boom sprayer of this size start with a bigger tip or a higher pressure. This case shows why tip size, pressure, boom height, and section control have to move as one set, because the flow arithmetic was nearly identical before and after the change.

The method transfers in four steps. Set the flow per nozzle from Q = L/ha x km/h x spacing / 600. Pick the tip size that reaches that flow at a pressure which holds the droplet class the label asks for. Set boom height from the covered width and the spacing, so the overlap band carries the coarser spectrum. Then let PWM hold the rate across the speed range and close sections one tip wide rather than one boom section wide.

Three thresholds travel to any 24 m machine. Keep tip flow within plus or minus 5 percent at the fill check and scrap a tip at plus 10 percent. Keep the volume below 150 µm under about 5 percent if drift is the problem, because VMD alone will not tell you. Keep the count above 20 drops/cm² for systemic products and above 30 for contact products, measured on water sensitive paper rather than assumed.

The maintenance logic is the other half. A worn air induction tip both over-applies and loses part of its drift advantage, so log the rail pressure at the boom inlet at every fill and the flow from one nozzle per section each week.

The same arithmetic runs on an 18 m mounted machine or a 36 m self-propelled machine with a change of width and spacing, and the three point sprayer notes cover the smaller end of the same choice. For boom sprayer nozzles on a row-crop program, send the boom width, the nozzle spacing, the label rate, the speed range, and the droplet class the product requires to the BoreJet application team through the contact page, and the tip size, the pressure, and the duty range come back as one set.