Agricultural spray tanks: capacity, materials, agitation and replacement checks

The tanks on a sprayer and what each one holds

Every crop sprayer carries several tanks. The largest holds spray liquid. A fresh-water tank for cleaning must hold at least 10% of the rated tank volume, or ten times the dilutable residual quantity. A third, smaller tank, usually 10 to 20 litres, supplies water for washing protective equipment and nozzles in the field.

The induction bowl, usually around 45 litres, makes filling with plant protection products easier and has canister-flushing nozzles for cleaning the containers at once. The extra tanks and the bowl are made of the same material as the main tank.

The HARDI FrontTank works as a nurse tank that brings more water into the field: the water is sucked into the main tank, chemicals are added and spraying continues without a trip back to the filling station. With an agitation pump kit and an electric valve kit, the same tank becomes a separate chemical tank. The return from sections and agitation stays active on the main sprayer, so the operator has to control that the main tank is not overfilled. The front tank has a standard 135-litre rinse tank. Amazone sells its front tanks for the UF mounted sprayers: the FT 1502 adds 1,500 litres to a UF 02, so a UF 2002 reaches 3,500 litres, and Amazone says it has offered the FT 1001 front tank for many years. With Amazone's FlowControl+ the liquid moves between the front and rear tanks, and the fill levels in both are controlled from an ISOBUS terminal. An Amazone front tank, a HARDI one or any other maker's is checked the same way. Before you accept a front-tank installation, ask the installer to show the whole sequence: which pump moves the liquid, which valves choose the supply and where the return goes. At handover, check which level reading tells you to stop a transfer, and label the controls with the names used in the manual so another operator can follow the same procedure.

Before you choose a size, write down what the tank is for: spray mixture, nurse water, rinse water or washing water. Ask the supplier which connections and controls serve each circuit. On a farm where several operators share the tractor, label "front water" and "front mixture" separately so nobody mistakes one for the other. If you buy a used tank, ask the seller for its history and what it held before.

Rated capacity and working fill

When you read a quotation, check which figure it gives: rated volume or total physical volume, and in which unit. If an advertisement is in gallons, ask the supplier for the figure in litres before you use it in a load plan. Do not judge the filling limit by eye from the brim.

The actual volume of the tank must be at least 5% higher than the rated volume. For portable sprayers, the nominal maximum filling level marked on the tank is no more than 95% of the total volume, and a tank holds at least 5 litres. A 15-litre knapsack tank is therefore marked at no more than 14.25 litres, and a 1,000-litre rated tank holds at least 1,050 litres.

Tank materials

Most tanks are glass-fibre-reinforced plastic (GFK) or polyethylene (PE); some are stainless steel. The FrontTank vessel is high-impact polyethylene. All three are smooth inside and similar in weight. They differ in UV stability (GFK poor, PE average, stainless steel good), mounting points (GFK poor, PE average, stainless steel good) and repair (GFK good, PE average, stainless steel good).

Parts of a portable sprayer that touch spray liquid are made of non-absorbent materials unaffected by approved pesticide formulations, and parts exposed to sunlight do not degrade under long UV exposure.

When you order a replacement, give the supplier the marking on the old tank, the machine model, the serial number and what the tank will hold, and ask for the material, seals and gaskets to be confirmed in writing. Do not judge the material by colour or look. Ask how sunlight, storage and your cleaning products affect that particular tank. If the tank is damaged, describe where and how, and ask the manufacturer whether to repair or replace it rather than patching it yourself.

Mounting and connections

Before the old tank comes out, take photographs and measure the frame, cradle, straps, clearances and access points, and send them to the supplier. Ask which mounting parts come with the new tank and which of the old ones you can reuse. For a front tank, check access, visibility and the transfer arrangement on the whole tractor and sprayer combination. For an ATV or quad, name the carrier, rack and mounting kit in the same enquiry: the catalogue capacity describes the tank, not whether your vehicle can carry it.

Have a technician identify every connection from the machine documentation, not from where a hose happens to lie on the frame, and keep that sketch with the parts order. Give the supplier this for each fitting:

Mark any plumbing that was modified apart from the original, and ask the service agent whether it still suits the new tank. After installation, keep the final circuit drawing.

Agitation and pump capacity

Ask for the manufacturer's setup procedure for the agitator you have, and note which controls to use while filling, spraying and cleaning. If you change to a tank of a different shape, ask whether the old agitator layout still works, because the same volume can need different internal fittings. If operators report sediment or uneven mixing, describe what you see and the sprayer's configuration to the technician instead of changing connections by trial and error.

The pump output must supply both the boom and the agitation. The flow the boom needs in litres per minute is working width (m) × application rate (l/ha) × driving speed (km/h) ÷ 60.

The agitator needs 5% of the rated volume per minute for tanks up to 1,000 litres, 60 litres per minute for 1,000 to 2,000 litres, and 3% of the rated volume above 2,000 litres. At high water volumes and high driving speeds the agitation must be strong enough to prevent the spray liquid from demixing.

The simplest agitator is a pipe with holes that gives visible circulation. Injector agitators reach awkward corners of irregular tanks at lower flow, and several injectors avoid dead areas. Mechanical agitators need no pump capacity. Piston diaphragm and piston pumps are the usual choice; with piston diaphragm pumps two are often fitted, one for spraying and one for agitation, and both run together while filling. The pump's position in the sprayer decides whether it can be repaired without dismantling the whole sprayer. A separate cleaning pump usually runs at 90% of the nozzle output. On portable sprayers an agitator is desirable; if fitted, it must move freely, must not catch on other parts of the sprayer, and must be easy to fit and remove with gloved hands.

Piston diaphragm pumps run dry and self-prime well. Piston pumps are bulkier and heavier, with a lower delivery rate. Centrifugal pumps are compact and light with a high delivery rate, which suits filling because the highest pump capacity is needed during intake, but they do not self-prime and need a design protected against running dry. Centrifugal pumps are gaining importance because an oil motor regulates their flow independently of the tractor's engine speed. All three types resist the material and handle liquid fertiliser well.

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Fill opening, strainer, lid and level

On portable sprayers the strainer mesh opening is no larger than 0.5 mm. The strainer sits recessed in a fill opening at least 100 mm across, shows the maximum fill mark clearly, and does not lift from its seat while filling. The lid closes securely with gloved hands and no tools, does not collect spray liquid, and either the lid or the tank has a ventilation valve.

The FrontTank has a liquid-free level indicator on top, visible from the driver's seat. Ask how the operator will read the level while filling and while working, and check that the planned installation leaves the indicator in view from the driving position. Pressure and flow controls on portable sprayers can be adjusted from outside the tank.

Marking, spare parts and build quality

A portable sprayer carries a durable mark with the manufacturer's name and address, sprayer name, model and year of manufacture. The manufacturer keeps specifications and model details so replacement parts can be identified for at least five years after manufacture.

A sprayer built to the FAO specification keeps working and does not deform or leak if dropped, withstands 250 hours of continuous full-capacity operation, and has a safety device that stops pressure exceeding 5 bar anywhere in the system, venting liquid back into the tank. The tank strainer is supplied with the sprayer, easy to remove and fit in protective gloves, and its mesh is securely fixed to the strainer body.

Which sprayer carries which tank

A mounted sprayer with a front-mounted tank scores good for efficiency, manoeuvrability and equipment, average for operating comfort, poor for flexibility and very good for capital requirement. A self-propelled sprayer scores very good on efficiency, manoeuvrability, comfort and equipment, but poor for flexibility and capital requirement. Tank size follows the machine. Mounted sprayers carry 1,000 to 1,500 litres for a 15 to 18 m boom. Platform-mounted sprayers carry 2,000 to 4,000 litres for 21 to 27 m. Trailed sprayers carry 2,500 to 5,000 litres for 24 to 36 m, and self-propelled sprayers 4,500 to 6,000 litres for 27 to 36 m.

Hoses, valve and filters on a portable sprayer

Hoses on a portable sprayer must not kink when bent through 180 degrees at a 50 mm radius, and their connections must be adjustable with gloved hands and reconnect without loss of performance. The lance has a trigger valve that locks in the off position and opens with no more than 1.5 Nm of torque. A removable filter with a mesh of 0.3 mm or finer sits upstream of that valve. The lever is at least 100 mm from the pivot. The hose is long enough for free movement of the lance, which measures at least 500 mm from the trigger grip to the nozzle, has a bend so the spray can be angled downwards, and has a secure parking position when not in use.

Residues and cleaning

When you buy or replace a tank, ask the supplier which parts of the circuit hold liquid back and how the cleaning system deals with them, and ask for confirmation that the drain and rinse arrangement match your machine. Follow the product label when you change treatments. See the compatibility guide for mixing and the waste guide for disposal.

The more liquid stays in the tank after "spraying empty", the harder the whole machine is to clean, so the interior should have few internal fittings. On a portable sprayer the remaining volume in tank, pump and compression chamber should not exceed 100 ml.

A field sprayer is designed so that the lines can be flushed with the tank filled to the rated volume, the residual quantity diluted, and the inside and outside of the machine cleaned. One pump of a twin-pump system or a separate cleaning pump drives the cleaning. A separate pump between the fresh-water tank and the internal cleaning nozzles usually means a continuous internal cleaning system.

Spray tank sizes: gallons to litres for 10, 25, 100 and 300 gallon sprayer tanks

Irish sprayers and spray tanks are rated in litres. Tanks listed from abroad are rated in gallons, and there are two gallons: a US gallon is 3.785 litres and an imperial gallon is 4.546 litres. Ask the seller which one the listing means before you compare a tank with your sprayer.

The same question comes in litres: a 60 litre weed sprayer, a 100 ltr spray tank or 100 ltr spray unit, a 200 ltr spray tank, a 200 litre spray tank for sale and a 600 litre spray tank for sale are read straight against the rated capacity and working fill. So are a 50 litre, 300 litre, 500 litre and 1000 litre spray tank: divide the litres by your application rate in litres per hectare to see how many hectares one fill covers. Weigh the full tank as well: one litre of water weighs one kilogram, so a 600 litre tank adds 600 kg to a quad, UTV or small tractor before the frame and pump, and a 1000 litre tank adds a tonne.

Types of spray tank: fibreglass, metal, pressurised, battery, wheeled and tractor tanks

Name the material and the carrier when you ask for a tank, and ask the supplier in writing which products the material is approved for. Fibreglass (fiberglass) spray tanks and metal sprayer tanks differ in UV stability, mounting points and repair, so the supplier's compatibility statement decides, not the price.

A pressurised (pressurized) sprayer tank is filled and pumped to pressure by hand or by a pump; a battery sprayer tank or battery powered sprayer tank carries its pump and charger with it. Check the charge time and the spray time on a full charge against the area you treat in a day. A 12v spray tank unit runs its pump from a 12 volt battery, often the quad's or tractor's: ask for the pump's current draw and check that the wiring and the battery can carry it for a full day's work.

For a spray tank on wheels, a pull tank sprayer, spray tanks for tractors or a John Deere sprayer tank, check the hitch, the tyres and the loaded weight against the towing vehicle. For a spray tank for a quad bike, a UTV sprayer tank, a tank sprayer for a 4 wheeler or an IBC tote sprayer, check the loaded weight on the rack and where the liquid sits when the tank is half empty.

Look at the extras too: spray tank lids need a seal and a vent, a hose reel for a sprayer tank needs a hose long enough for the field edge, and a backpack spray tank needs a harness that carries a full load comfortably. Keep the tank's manual and its rated capacity with the sprayer file.

Next step

Compare the tank with the boom, pump and chassis in the sprayer selection guide, and work out area and quantities in the tank calculator.