How to Select Nozzles for Pull-Behind and Tow-Behind Sprayers

A nozzle mistake on a pull behind sprayer is expensive in two ways. The chemical cost is the obvious one. A boom running tips that are 10 percent oversized applies 10 percent more product per acre. On a 100-acre pass at 40 dollars per acre of chemistry, that is 400 dollars wasted before you even see a streak. The hidden cost is control: an undersized or worn tip leaves weed escapes and insect survivors that need a second pass at full price.

The fix is math, not luck. One formula sizes every nozzle on the boom. One chart turns the answer into a color you can buy. One 20-minute calibration confirms the rig before the season starts. This guide walks those steps for pull-behind and tow-behind sprayers, using the public extension numbers: 20-inch spacing, 30 to 40 psi, and the GPM formula. By the end you can size every nozzle from a product label and a tape measure.

Pull-Behind and Tow-Behind Sprayers: Know What You Are Sizing

A pull behind sprayer and a tow behind sprayer are the same machine under two names. Both are a tank on its own wheels, towed by a truck, an ATV, or a tractor, with a pump and a boom. The nozzle math does not change between them, because the pump, plumbing, and boom work identically. What changes is scale, and scale feeds the formula: boom width, tank size, pump flow, and travel speed.

Most ag sprayers in this class carry a 100 to 1,000 gallon tank and a 10 to 60 foot boom. The nozzles on that boom are flat fans spaced 20 inches apart, sized for 30 to 40 psi. That configuration is the agricultural default because it is cheap, simple, and predictable. Nozzle count scales with width: a 60-foot boom at 20-inch spacing carries 36 tips, all delivering the same gallons per minute.

Other sprayer types use different nozzle logic, so compare the classes before you buy.

Sprayer type	Typical tank	Typical boom or target	Nozzle family
Pull-behind / tow-behind	100-1,000 gal	10-60 ft boom	Flat fan, 65-110 degrees
3-point mounted	50-300 gal	10-30 ft boom	Flat fan, same math
ATV / UTV sprayer	15-60 gal	4-10 ft boom	Flat fan, lower GPA
Boomless sprayer	100-500 gal	15-40 ft fan	Deflector or wide fan
Mist sprayer	50-500 gal	Tree canopy	Hollow cone, 150-300 psi
Groundwork manual hose end sprayer	1-4 gal	Hand wand, lawn	Dial siphon, no flow math

A groundwork manual hose end sprayer is fine for a home lawn, where the dial on the siphon replaces flow math. Field work is different. Every 20-inch section of a field boom carries its own gallon-per-minute requirement, and guessing that number is where most application problems start.

Boomless sprayers throw a fan from a single deflector tip, not a row of nozzles, so coverage is coarser and less even at the edges. They suit pastures and fence lines where a boom cannot fit. On a boomless rig, the spacing term W becomes the swath width.

The One Formula That Sizes Every Nozzle

Every broadcast nozzle on a boom is sized with the same equation:

GPM per nozzle = (GPA x MPH x W) / 5940

Three inputs, one answer:

GPA: gallons per acre from the product label. Herbicide labels commonly call for 10 to 20 GPA. Insecticide programs run 15 to 40 GPA.
MPH: actual ground speed, measured with a stopwatch, not read from the tractor dash.
W: nozzle spacing in inches. 20 inches is the standard, 30 inches appears on row rigs, and 15 inches shows up on some small booms.

The constant 5940 is just the unit conversion. It folds feet per mile, inches per foot, minutes per hour, and square feet per acre into one divisor.

Worked example one. Target 15 GPA, ground speed 6 MPH, spacing 20 inches.

GPM = (15 x 6 x 20) / 5940 = 1800 / 5940 = 0.303 GPM

Round to the nearest tip size: 0.30 GPM at 40 psi. That is a blue 11003 flat fan, meaning 110 degrees and 0.30 GPM.

Worked example two. Target 20 GPA, speed 8 MPH, same spacing.

GPM = (20 x 8 x 20) / 5940 = 3200 / 5940 = 0.539 GPM

That rounds to a brown 0.50 GPM tip. Notice the pattern: at 20-inch spacing, every bump in speed or rate pushes you to the next color up the chart.

Worked example three, banding. A band application uses the band width as W. For a 10-inch band at 10 GPA and 7 MPH:

GPM = (10 x 7 x 10) / 5940 = 700 / 5940 = 0.118 GPM

That lands on a purple 0.10 GPM tip. Banding is why one sprayer can carry two very different tip sets in a season.

Speed is the input people get wrong most often. GPA and GPM move in opposite directions with speed. If you plan for 5 MPH but actually cover the field at 6 MPH, the applied rate drops 17 percent. That is the difference between a clean pass and a weed escape. Measure speed the honest way: mark 100 feet, time the run, and divide 68.18 by the seconds. An 11.4 second run equals 5.98 MPH.

Pressure is a trim control, not a size control. Flow scales with the square root of pressure. Doubling pressure from 30 to 60 psi raises output only 41 percent, and it shreds the droplet spectrum into drift-prone fines. Set pressure at 30 to 40 psi and pick the tip size from the chart. Use pressure to fine-tune the last 5 to 10 percent, nothing more.

Color Codes and the Flow Chart

The color-code system started with TeeJet, and every nozzle vendor copies it now. The color printed on the tip states flow at 40 psi. The number states angle and flow: 8004 means 80 degrees and 0.40 GPM at 40 psi, while 11004 means 110 degrees at the same flow. The last two digits are GPM multiplied by 100. If reading a full chart feels unfamiliar, our step-by-step guide to reading a TeeJet nozzle chart walks every column.

The standard flat fan chart at 40 psi, in the extended-range family that most ag sprayers run:

Color	Code examples	GPM at 40 psi
Purple	8001 / 11001	0.10
Green	80015 / 110015	0.15
Yellow	8002 / 11002	0.20
Blue	8003 / 11003	0.30
Red	8004 / 11004	0.40
Brown	8005 / 11005	0.50
Gray	8006 / 11006	0.60
White	8008 / 11008	0.80
Light Blue	8010 / 11010	1.00
Light Green	8012 / 11012	1.20
Orange	8015 / 11015	1.50
Black	8020 / 11020	2.00

The 0.20 to 2.00 GPM band covers nearly all boom work on pull-behind machines. Below 0.20 GPM you are in lawn or banding territory, where finer screens and lower speeds matter more. Above 2.00 GPM you are usually spraying liquid fertilizer, where the same formula still applies but the spacing and speed assumptions change.

Two cautions. The color states flow only, never droplet size: two same-color tips can spray very different droplets. And ratings assume clean water at 40 psi, so thick liquids and worn orifices shift the real number.

Angle and Spacing: Coverage Without Streaks

Boom height and nozzle angle must agree, or you get stripes. A flat fan spreads wider as it falls, and the geometry is simple. Spray width at the target is roughly twice the height times the tangent of half the angle. A 110-degree fan at 20 inches above the crop covers about 57 inches. With tips spaced 20 inches apart, that is a two-and-a-half nozzle overlap, and that overlap is what makes the pattern even. The same math and the same families apply across the whole agricultural range; our agricultural nozzle overview lays out the full pattern picture.

Common working sets used on field booms:

Nozzle angle	Nozzle spacing	Boom height	Typical job
110 degrees	20 in	18-24 in	Standard broadcast herbicide
80 degrees	20 in	24-30 in	Lower drift, tighter pattern
65 degrees	30 in	30+ in	Row-crop bands, wide rigs

Run the numbers the other way when you change a boom. On 30-inch spacing, a 110-degree nozzle needs the boom near 30 inches high to overlap evenly, and a 65-degree fan distorts less at the edges.

Do not mix angles on one boom. A single 80-degree tip on a 20-inch, 110-degree boom leaves a thinner strip, and that strip shows up as a streak in the field. Keep every tip on a section the same angle, the same size, and the same family. Ag spray coverage is only as even as the worst nozzle on the boom.

Anti-drip checks matter too. A leaking check valve drips product onto one spot while the rig sits at the headland, and the overdose burns a strip. Fit the drip guards the nozzle family calls for, and replace them when they weep.

Herbicide and Insecticide Nozzles: Match the Chemical Job

Droplet size is the connection between nozzle and chemical. The ASABE standard classes droplets by diameter in microns: fine is 145 to 225, medium is 226 to 325, coarse is 326 to 460. The drift-prone fraction is droplets below roughly 150 to 200 microns. Your nozzle choice is really a droplet size choice, made for a specific chemical program.

Herbicide programs. A weed killer sprayer running post-emergence products wants medium to coarse droplets, roughly 300 to 500 microns, at 10 to 20 GPA. Systemic herbicides such as glyphosate and 2,4-D translocate once they land, so they need droplets that hit the leaf and stay, not a fine mist. Standard flat fans at 30 to 40 psi deliver that.

Pre-emergence products are soil-applied and even more forgiving. They run coarse droplets at 15 to 20 GPA with flat fans, and some rigs use flood tips. The goal is even soil coverage, not canopy penetration.

Insecticide and fungicide programs. An insecticide sprayer job is the opposite of a herbicide sprayer job. Insects hide on leaf undersides and inside the canopy, so coverage matters more than droplet size. Fine to medium droplets at 15 to 40 GPA wet more leaf surface. Flat fans still work, and a 110-degree fan at 20-inch spacing is the standard. For deep canopy work, hollow cone tips at higher pressure push product where fans cannot reach, which is the classic mist sprayer setup.

The tradeoff rule. Contact products, which must touch the pest, want the finest droplets the conditions allow. Systemic products tolerate coarser droplets. Every step coarser cuts drift but also cuts coverage, so the drift decision and the coverage decision are the same decision made once.

Program	Droplet class	Typical GPA	Typical tip
Post-emergence herbicide	Medium to coarse	10-20	Flat fan, 110 degrees
Pre-emergence herbicide	Coarse	15-20	Flat fan or flood
Insecticide / fungicide	Fine to medium	15-40	Flat fan or hollow cone
Row banding	Medium	5-15	Narrow flat fan, 65-80 degrees

Drift Control: The Numbers That Matter

Drift is measured in dollars and in neighbor complaints. The operating rules are public and consistent across extension services:

Wind speed above 10 mph: stop broadcast spraying.
Wind below 3 mph at dawn or dusk: watch for temperature inversions that hold fine droplets aloft.
The drift fraction is droplets under roughly 150 to 200 microns. Coarser droplets fall faster and land closer to the boom.

Air induction nozzles are the biggest single fix. Venturi tips pull air into the spray stream and produce large, air-filled droplets that burst on contact with the leaf. Field trials consistently show 50 to 90 percent drift reduction versus standard flat fans at the same flow. They cost a little more and need 30 to 40 psi to open, exactly this guide’s range.

Boom height matters as much as nozzle choice. Every extra inch of height gives a droplet more time to be carried off-target. Keep the boom at the lowest height that still gives even overlap: 18 to 24 inches for 110-degree tips at 20-inch spacing.

Buffer zones and labels set the legal floor. The drift statement on the label is a requirement, not advice, and no nozzle choice overrides it.

Adjuvants change the picture. Drift retardants thicken the spray and shift the droplet spectrum coarser, making a standard flat fan behave more like an air induction nozzle. Verify label compatibility before building a nozzle set around one.

If you are also comparing aerial coverage for the same crop, the droplet logic carries over, but the numbers do not. Our guide to drone spraying nozzle selection covers the air-side version of this decision.

Match the Pump, Filters, and Agitation

The nozzle is the last link in a chain, and the chain fails at its weakest point. Size the rest of the rig with the same care as the tips.

Pump capacity. Total pump flow must cover nozzle flow plus agitation plus margin. The rule of thumb: nozzle flow, plus 20 percent, plus 3 to 5 GPM per 100 gallons of tank for agitation. A 300-gallon pull behind sprayer with 30 nozzles at 0.40 GPM needs 12 GPM for the boom. Agitation adds 9 to 15 GPM. With the 20 percent margin, the pump should deliver 25 to 32 GPM. Undersize the pump and the far end of the boom starves first.

Filters. Every flat fan should have a screen upstream. The common rule is 50-mesh for tips above 0.30 GPM and 100-mesh for the fine tips below. A suction strainer protects the pump. An inline strainer at each boom section protects the tips. A plugged screen starves the nozzle into a skip pattern that looks like a worn tip.

Agitation. Powders settle fast. Wettable powder formulations need continuous agitation, and the bypass line is the usual agitation source on pull-behind rigs. Run the agitation loop whenever the pump runs, including during turns and refills.

Pressure gauge placement. Read pressure at the boom, not the pump: fittings, filters, and hose bends eat pressure, so the pump gauge overstates what tips see. A 5 psi drop at the boom means roughly 6 percent less flow.

Tank and plumbing. A 10 percent flow restriction anywhere in the line changes every nozzle downstream, so keep boom plumbing at or above the pump outlet size.

Calibration in Five Steps

Calibration is a 20-minute job with a stopwatch, a jug, and a calculator. Do it at the start of the season and again every time you change chemicals or speed.

Step one: measure spacing. W is the distance between nozzles in inches, usually 20. Write it down, because the formula uses it twice.

Step two: measure speed. Mark 100 feet, time the rig, and divide 68.18 by the seconds. Run the pass in the gear and throttle you will actually use, with the tank half full.

Step three: read the label. Find the target GPA for the product and the pest.

Step four: solve the formula. GPM = (GPA x MPH x W) / 5940, then pick the tip color from the chart.

Step five: catch-test the boom. The 1/128-acre method is the field standard. With 20-inch spacing, measure 204 feet of travel. Catch each nozzle for the time it takes to cover that distance, then read the ounces as GPA. One ounce collected equals one gallon per acre applied. Any tip more than 10 percent off is dirty, worn, or wrong, and it gets fixed before you spray.

Recheck after the first full tank. Pump wear, filter buildup, and gauge drift all shift output over a season. The 10 percent rule catches them all: a tip flowing more than 10 percent over rating comes off the boom.

Common Mistakes

Seven errors cause most of the streaks, skips, and overdoses on pull-behind rigs:

Wrong spacing in the formula. Using 30 inches instead of 20 changes the answer by 50 percent, and the boom gets nozzles two sizes too big.
Pressure too high. Above 40 psi, droplets go fine, drift climbs, and tips wear faster.
Guessing speed. A 10 percent speed error is a 10 percent rate error in the opposite direction.
Mixed tip sizes or angles on one boom. One odd tip makes one permanent streak.
Worn nozzles left on the boom. Replace any tip that flows more than 10 percent above its rating.
The wrong filter mesh. Too fine a screen starves the tip, and too coarse a screen lets grit erode the orifice.
Spraying in wind above 10 mph with standard flat fans. Switch to air induction tips or wait for calmer conditions.

FAQ

What is the difference between a pull behind sprayer and a tow behind sprayer?

None mechanically. The names describe the same trailed machine, and nozzle sizing is identical for both. Pick one term for your records and stay consistent.

How do I know what GPM my nozzles need?

Run the formula GPM = (GPA x MPH x W) / 5940 with the label rate, a measured speed, and your spacing in inches. The three worked examples above cover broadcast, high-rate, and banding cases.

Why do nozzles come in colors?

The color code states flow in GPM at 40 psi. Yellow is 0.20, blue is 0.30, red is 0.40, and the chart continues up to black at 2.00. It is the fastest way to verify a boom at a glance.

Should I use 80 or 110 degree nozzles?

Use 110 degrees for 20-inch spacing at an 18 to 24 inch boom height. Use 80 degrees for the same spacing with the boom raised to 24 to 30 inches, or when you want a tighter pattern. Match the angle table above.

How often should I replace nozzles?

Catch-test at least twice a season and after every abrasive application. Replace any tip that flows more than 10 percent over its rating. Brass tips wear fastest, stainless lasts longer, and ceramic lasts longest.

Can air induction nozzles be used for insecticides?

Yes, with a tradeoff. Coarser droplets reduce drift and also reduce leaf-underside coverage. For insects, fine to medium flat fans are usually the better match, and air induction tips are best reserved for herbicide passes near sensitive areas.

Final Checklist

Print this before you calibrate.

Get the Nozzles Right the First Time

The difference between a clean season and a frustrating one is usually a 20-inch spacing and a 40 psi reading, not a fancier machine. Run the formula once, buy the colors it points to, and confirm with one catch test. That sequence covers every acre your rig will touch this year.

Ag spray equipment buyers compare flow ratings before anything else, so our catalog lists GPM at 40 psi for every tip. That lets the chart above map straight onto the product pages. Browse the agricultural nozzle range for flat fans, air induction tips, and screens sized to your boom. Send your sprayer specs to our team for a nozzle list matched to your tank, pump, and chemical program. Start with the agricultural nozzle lineup, and contact us when you want a second set of eyes on the math.