Table of Contents
A sprayer tank that runs dry 150 feet before the headland leaves a strip no later pass can fix. On a 400 gallon rig running 20 GPA, the starved pass is the last one, and the skip lands at the field edge where weed pressure is often heaviest. The same tank, sized and agitated correctly, finishes with 40 gallons in reserve.
Tank decisions are made before the pump runs. Volume sets acres per fill. Agitation flow sets whether a wettable powder stays mixed or beds out. Sump geometry and cleanout set whether the next chemistry starts clean or carries residue into a sensitive crop. This guide works all three against label rates, with numbers you can recompute on your own rig.
The Snapshot
- Acres per fill: usable volume divided by the carrier rate. A 400 gallon sprayer tank at 20 GPA covers 20 acres on paper and 15 acres with a quarter tank held for turns and rinse.
- Agitation flow: published guidance runs 3 to 5 gpm per 100 gallons of tank volume. A 400 gallon sprayer tank needs 12 to 20 gpm of jet or bypass flow.
- Small rigs size the same way. A 15 gallon sprayer tank at 20 GPA covers under an acre per fill, and a 25 gallon unit still needs a quarter held back for turns and rinse.
- Sump design: a sloped floor should leave under 1 percent of tank volume behind. That is under 4 gallons in a 400 gallon tank and under 0.25 gallons in a 25 gallon sprayer tank.
- Cleanout: a triple rinse uses three passes at about 10 percent of tank volume each. That is roughly 120 gallons on a 400 gallon tank and 7.5 gallons on a 25 gallon sprayer tank.
When the Tank Becomes the Failure Point
Most application defects get blamed on the nozzle. Many start in the tank. Four failure modes cover the range.
A short fill. The suction strainer uncovers on a slope when the level drops below about a quarter full. The pump pulls air, line pressure falls, and the far boom section thins out. The result is a striped headland.
Settled product. A wettable powder in still water can form a bed within 15 to 30 minutes. Without agitation the last third of the tank goes out weak. The bed that stays behind then slugs through the lines at the next fill.
Residue carryover. A tank that was drained but not rinsed holds a film of concentrate on the walls and in the sump. That film redissolves into the next mix and carries an active ingredient into a crop the label never allowed.
Herbicide injury. Auxin and sulfonylurea residues can injure a following broadleaf crop at a few parts per billion in the spray solution. That level is far below anything the eye can detect, so the damage appears without warning.
Sizing Tank Volume to Acres or Hectares per Fill
Tank volume is a coverage decision, not a capacity contest. The arithmetic is one line:
acres per fill = usable tank volume / carrier rate
The carrier rate comes from the label, not from habit. Herbicide labels commonly call for 10 to 20 GPA. Insecticide and fungicide programs run 15 to 40 GPA. Band and spot work applies the same rate over a fraction of the acre.
Worked example, farm rig. A 400 gallon sprayer tank at 20 GPA covers 400 / 20 = 20 acres. Hold a quarter of the tank for turns and rinse and the working figure is 15 acres. The same tank at 40 GPA drops to 10 acres nominal and 7.5 acres usable.
Worked example, small rig. A 25 gallon sprayer tank at 20 GPA covers 25 / 20 = 1.25 acres. At a 40 GPA spot rate over treated ground it covers 0.63 acres.
Metric rigs use the same line. A 1000 L tank at 200 L/ha covers 5 ha, and most European field programs sit between 100 and 300 L/ha.
| Tank size | At 10 GPA | At 20 GPA | At 40 GPA |
|---|---|---|---|
| 15 gal | 1.5 acres | 0.75 acres | 0.38 acres |
| 25 gal | 2.5 acres | 1.25 acres | 0.63 acres |
| 50 gal | 5.0 acres | 2.5 acres | 1.25 acres |
| 100 gal | 10 acres | 5.0 acres | 2.5 acres |
| 200 gal | 20 acres | 10 acres | 5.0 acres |
| 300 gal | 30 acres | 15 acres | 7.5 acres |
| 400 gal | 40 acres | 20 acres | 10 acres |
| 1000 gal | 100 acres | 50 acres | 25 acres |
Subtract the unusable fraction before you plan the day. A tank heel plus the quarter kept back for stability takes 20 to 30 percent off the nameplate figure. That reserve keeps the suction covered through a turn.
The Carrier Volume Arithmetic Behind Every Fill
Area per fill answers how far the tank goes. Flow per nozzle answers whether the boom matches the label. The carrier-volume equation ties the two together:
gpm per nozzle = (GPA x mph x W) / 5935
GPA is the label rate. mph is measured ground speed, not the dash reading. W is the width each nozzle treats in inches. The divisor 5935 folds feet per mile, inches per foot, minutes per hour, and square feet per acre into one constant. In metric units the form is L/min = (L/ha x km/h x W) / 600, with W in metres.
Worked example. A 60 ft boom at 20 inch spacing carries 36 nozzles. Target 15 GPA at a measured 6 mph.
gpm = (15 x 6 x 20) / 5935 = 1800 / 5935 = 0.303 gpm per nozzle
The whole boom passes 36 x 0.303 = 10.9 gpm. Push that against a 300 gallon fill and the tank sprays for 300 / 10.9 = 27.5 minutes before it runs dry.
Metric example. A 0.5 m nozzle spacing at 200 L/ha and 7 km/h.
L/min = (200 x 7 x 0.5) / 600 = 700 / 600 = 1.17 L/min per nozzle
Refill timing. Field capacity in acres per hour is close to mph x boom width in feet / 8.25. A 6 mph pass with a 60 ft boom works out to 43.6 acres per hour at full width. Allow 75 to 85 percent for turns and refills and the real figure lands near 33 to 37 acres per hour. At 15 GPA that burns 10 to 11 gpm, which matches the boom total above.
Dilution volume. Mix volume is the carrier volume for the treated area plus the product. A 5 ha block at 200 L/ha needs 1000 L of water. At a 2.0 L/ha product rate it needs 10 L of product. A 200 L sprayer tank fills that block in five loads of 200 L water and 2 L product each. Add product to water already in the tank, never the reverse, and keep the label order for tank mixes.
One speed note. GPA and gpm move in opposite directions with speed. Plan for 6 mph and drive 7 mph and the applied rate drops about 14 percent. Measure speed over a marked 100 ft run and divide 68.18 by the seconds.
Agitation Types: Paddle, Jet, and Recirculation Compared
Agitation keeps solids suspended and keeps the mix uniform from the fill to the last gallon. Three systems do that work.
A mechanical paddle agitator turns on a shaft through the tank wall. Typical speeds run 100 to 300 rpm, and the paddle tip moves at about 1.5 to 3 m/s. It mixes wettable powders well, and its flow does not depend on the pump.
Jet agitation uses nozzles on the tank floor or the bypass line to sweep pump flow across the bottom. It is the common choice on farm sprayer tanks because it needs no shaft seal and no extra drive. Each jet typically passes 2 to 8 gpm, depending on its orifice and the line pressure.
Recirculation returns unused pump flow to the tank through a return line. It keeps the mix moving and warms the lines on cold mornings, but the return flow collapses when the boom opens.
| Agitation type | Typical flow | Formulation fit | Points to check |
|---|---|---|---|
| Mechanical paddle | Not tied to pump, tip speed 1.5 to 3 m/s | Wettable powders, slurries | Shaft seal wear, clearance to baffles |
| Jet or bypass | 3 to 5 gpm per 100 gal | Wettable powders, suspensions | Jet aim, pressure at low tank level |
| Recirculation return | Falls as the boom opens | Soluble liquids, light mixes | Return line size, check valve |
| No agitator | Zero | Soluble liquids only, short fills | Settling, stratification |
Sizing Jet and Bypass Agitation Flow for Suspension Hold
Agitation flow is sized from tank volume, not from a guess. On farm sprayer tanks, the published rule for suspension work is 3 to 5 gpm of agitation per 100 gallons of tank volume.
Worked example. A 400 gallon sprayer tank needs 400 / 100 x 4 = 16 gpm of agitation at the mid-point of that range. Converted, 16 x 3.785 = 60.6 L/min.
If the rig uses three jet nozzles, each one passes 16 / 3 = 5.3 gpm. Jet flow rises with the square root of pressure, so set loop pressure to the value the jet lists for that flow.
The hydraulic cost is small. Power in kW follows Q (L/min) x P (bar) / 612. At 2 bar:
kW = 60.6 x 2 / 612 = 0.198 kW = 198 W
That is under 0.2 kW of hydraulic work for full suspension agitation on a 400 gallon tank. The pump still has to supply boom flow plus agitation plus margin, so a rig with a 28 gpm boom and 16 gpm of agitation needs 44 gpm at the outlet.
Metric rigs follow the same ratio. A 1000 L sprayer tank at 3 to 5 percent of volume per minute needs 30 to 50 L/min of agitation flow.
Suspension hold. A wettable powder in still water can settle into a compact bed in 15 to 30 minutes. Agitation holds it and must run during mixing, spraying, and turns. A lump that never breaks down becomes a plugged nozzle later.
Tank Shape, Sloped Sump, and Dead Volume
A flat floor with a drain in one corner leaves a wedge of liquid that no pump can reach. A sloped sump fixes that. The floor falls toward a low point at 3 to 5 percent, and the suction draws from the deepest part. The unreachable volume should stay under 1 percent of nominal capacity, which is under 4 gallons on a 400 gallon tank.
The suction strainer sits 25 to 50 mm above the floor, or in a sump well below it. Too high and the tank leaves a large heel. Too low and the strainer pulls settled grit straight into the pump.
Baffles control slosh. A wide tank with no baffles surges on a slope or a turn, and the wave can uncover the suction for a second or two.
Vortexing is the last trap. As the level falls, the suction can form a vortex that pulls air even with liquid still in the tank. Most tanks show this below about 15 to 20 percent of capacity. That is the physical reason for the quarter-tank reserve, beyond simple caution.
Dead corners carry residue. A tank whose sump holds 20 gallons of a 400 gallon fill has 5 percent dead volume. If those 20 gallons are the strongest part of the mix, they enter the line as a slug at the end of the pass and can burn the last run.
Materials: Cross-Linked Poly versus Stainless
Cross-linked high density polyethylene is the default on farm and portable tanks. It resists most agricultural actives and takes impact without cracking. It needs UV stabilisation for years in sunlight, and aromatic solvents or some concentrated esters can swell it. Check the compatibility chart for the specific product.
Stainless steel, usually 304 or 316, handles a wider chemical and temperature range and holds its shape at higher fill and wash pressures. Grade 316 resists chlorides better than 304. It costs more and weighs more, and it is the choice where solvents or hot wash cycles are routine.
Seals and gaskets fail before the tank does. EPDM, Viton, and PTFE cover most agricultural chemistry, and the wrong elastomer swells or hardens in a season.
The 15 and 25 Gallon Hand and Portable Tanks
Small tanks follow the same arithmetic, with tighter margins. A 15 gallon sprayer is usually a hand or ATV unit with a 12 volt diaphragm pump rated 1.0 to 1.5 gpm. A 25 gallon sprayer tank adds range but not agitation power.
Coverage is small at these volumes. A 15 gallon sprayer at 15 GPA covers 1 acre. A 25 gallon sprayer tank at 20 GPA covers 1.25 acres. At a 40 GPA spot rate over treated ground, the 25 gallon figure falls to 0.63 acres.
Flow demand still sets the tip. A 6 ft boom at 20 GPA and 4 mph needs:
gpm = (20 x 4 x 72) / 5935 = 5760 / 5935 = 0.97 gpm
Divide that into a 25 gallon sprayer tank and the fill empties in 25 / 0.97 = 25.7 minutes of spraying. A 15 gallon sprayer at a single 0.2 gpm wand tip delivers about 75 minutes of trigger time, which suits spot work better than a full-coverage pass.
Agitation is the weak point in this class. Bypass flow on a small pump is a fraction of a gallon per minute, so wettable powders stratify quickly. Keep the bypass loop open whenever the pump runs and prefer soluble liquids on hand-carried rigs.
The backpack sprayer nozzle selection guide covers the walking version of this sizing job. For a boom that reaches past a small rig’s capacity, the boomless spray nozzle guide explains where a wide fan replaces a boom.
Cleanout: Triple Rinse, Cleaning Ports, and Spray Tank Cleaner Chemistry
Cleanout protects the next crop. The standard field protocol is the triple rinse, and the volumes follow tank size directly.
Each rinse uses clean water at about 10 percent of tank volume. Drain fully between rinses. Spray the rinse water out through the boom onto a labeled site, never into a ditch or a floor drain.
For a 400 gallon tank that is three passes of 40 gallons, or 120 gallons of water total. For a 25 gallon sprayer tank it is three passes of 2.5 gallons, or 7.5 gallons total. Small volumes are easy to run and easy to skip, and a tank used for two chemistries in a day should never skip them.
A spray tank cleaner covers the film that water alone leaves behind. Match the chemistry to the product family. Alkaline cleaners handle many pesticide residues, ammonia-based rinses are used for some sulfonylurea and amine salts at label dilution, and commercial cleaners carry their own dose rate. Never mix a chlorine source with an ammonia cleaner, because the reaction releases a toxic gas.
Cleaning ports and the drain are part of the system. A 25 to 50 mm drain valve empties the sump fast, and a rinse nozzle at the top of the tank wets the walls where residue clings. Clean the filters and the nozzle screens at the same time.
| Cleanout step | What to do | Volume or threshold |
|---|---|---|
| Drain | Empty the tank and the sump completely | Below 1 percent of tank volume left |
| Rinse one | Add clean water, run agitation, spray out | About 10 percent of tank volume |
| Rinse two | Repeat, including the boom and lines | About 10 percent of tank volume |
| Rinse three | Repeat, then drain the sump | About 10 percent of tank volume |
| Clean | Use a spray tank cleaner at label dose | Follow product label |
| Purge | Flush lines, boom, filters, and nozzles | Until clear water runs |
| Record | Note product, date, and rinse volume | Keep for the season |
Time the rinse to the chemistry. Some actives bind to the tank wall and need the cleaner step, while simple soluble salts rinse out in two passes. When the next crop is sensitive, add a rinse and spray the initial rinse water on a tolerant site.
Filling, Induction, and the ISO 16119 Checklist
Fill and induction practice decides how much product reaches the tank and how much reaches the operator.
A vent that cannot pass the fill flow is a hazard. A fast fill into a tank with an undersized vent builds pressure or vacuum and can deform a poly tank. Size the vent to the fill rate and keep it clear.
Induction hoppers reduce dust and spillage. Add product to water that is already in the tank, fill to roughly 50 to 75 percent before induction, and let the agitation run during induction. Never pour concentrate into an empty tank, where it can sit in the sump and resist mixing.
ISO 16119 sets the design frame for the filling and flushing connection, the anti-drip provision, and the rinse water supply. A tank built to that frame gives you a clean external fill point and a documented rinse volume. ISO 16120 covers sprayer nozzle test methods, which is the standard behind the flow checks you run on the boom.
Level indication matters more than it looks. A sight tube or a marked gauge with 10 percent steps lets the operator track the fill against the area covered.
Keep a clean water tank for hand washing and for rinsing a spill. Published sprayer design guidance commonly calls for a dedicated clean water supply of around 15 L on field equipment.
Failure Modes: Diagnose the Tank, Not the Nozzle
The tank and its plumbing produce their own symptoms.
| Symptom | Tank-side cause | What to check | Fix |
|---|---|---|---|
| Striping at the headland | Suction uncovers on a slope | Tank level, strainer height | Keep a quarter full, lower the strainer |
| Weak mix late in the pass | Settled solids, low agitation | Agitation flow against 3 to 5 gpm per 100 gal | Add jets, raise loop pressure |
| Plugged nozzles and screens | Grit and undispersed lumps | Screen mesh, induction practice | 50 mesh for standard tips, premix powders |
| Crop injury after a swap | Residue carryover | Rinse volume and cleaner step | Triple rinse, add the cleaner pass |
| Pressure pulsing and spitting | Air leak or vortex at low level | Suction joints, level at spray time | Tighten fittings, keep the reserve |
| Tank cracking or distortion | Undersized vent, swelling material | Vent flow, chemical compatibility | Resize the vent, check the seal family |
| Concentration burn at pass end | Dead corner releases a slug | Sump slope and dead volume | Slope to 3 to 5 percent, drain the heel |
Two rows are pure arithmetic. The agitation row is a volume ratio, and the dead-volume row is a percentage of tank capacity.
The nozzle side still matters. Flow per tip, pattern, and drift class decide where the spray lands once it leaves the tank. If you are sizing the boom as well, the spray nozzle flow rate calculation guide works the same carrier-volume equation from the tip end, and the guide to choosing a spray nozzle maps the families to the job.
Sprayer Tank Agitation and Sizing FAQ
How many acres will a 25 gallon sprayer cover?
At 20 GPA a 25 gallon sprayer tank covers 1.25 acres. At 40 GPA it covers 0.63 acres. Subtract a quarter of the tank for turns and rinse, which brings the working figure to about 0.94 acres.
How much agitation flow does a sprayer tank need?
Published guidance for suspension work is 3 to 5 gpm of agitation per 100 gallons of tank volume. A 400 gallon sprayer tank therefore needs 12 to 20 gpm, and a 25 gallon sprayer tank needs about 0.75 to 1.25 gpm. Soluble liquids tolerate less, wettable powders and suspensions need the full range.
What size jet nozzles should I fit for agitation?
Divide the target agitation flow by the number of jets. A 400 gallon tank at 16 gpm of agitation and three jets needs 5.3 gpm per jet. Set the loop pressure so each jet passes its rated flow, since jet flow rises with the square root of pressure.
How do I clean a sprayer tank between products?
Follow the triple rinse. Use clean water at about 10 percent of tank volume for each of three passes, drain the sump fully between them, and spray the rinse water onto a labeled site. Add a spray tank cleaner matched to the product family when the next crop is sensitive.
Does a poly spray tank handle every chemical?
No. Cross-linked polyethylene resists most agricultural actives, but aromatic solvents and some concentrated esters can swell it. Stainless steel handles a wider range, and the seals usually fail before the tank does. Check the compatibility chart for the exact product and the seal material.
Why does my boom lose pressure at the end of a tank?
The suction is pulling air as the level falls, often from a vortex below about 15 to 20 percent of capacity. Keep the tank above a quarter full on sloped or bumpy ground, check the strainer height, and confirm the vent is clear.
Size the Tank Around the Numbers That Hold
The tank stops being the weak link when three numbers agree. Usable volume against the carrier rate sets acres per fill. Agitation flow against tank volume keeps the mix in suspension. Sump depth and rinse volume keep the next chemistry clean.
Get those three right and the rest of the rig has a stable baseline. The nozzle math then lands on a mix that is uniform from the initial gallon to the last.
Ag buyers compare flow ratings before anything else, so our catalogue lists flow, angle, and material for every part. Browse the agricultural nozzle range for flat fans, jet agitators, and screens sized to your tank, and the spray gun range for wand work. The agricultural spraying application covers the wider duty picture. For a boom rig, the pull-behind sprayer nozzle guide sizes the tips the tank feeds. Coverage and drift follow the mix, and the sprayer nozzle pattern and drift guide and the herbicide drift nozzle selection guide cover that half of the job. Send your tank volume, pump flow, and chemistry to our team and we will check the numbers with you.
Next Step
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Send your flow, pressure, fluid and target coverage. We come back with nozzle options and figures, not a catalogue number.
Written by
Ray ChanIndustrial spray nozzle specialist. I size tank cleaning, atomizing, flat-fan and spiral nozzles against real duty conditions, flow, pressure, fluid and target, rather than catalogue numbers. Every guide here comes from actual sizing work.