Crop sprayers and diaphragm spray pumps: what to specify

Three kinds of sprayer, one set of questions

Sprayers for crops, orchards and gardens come in three broad sizes. Manual knapsack sprayers are pumped by hand. Battery knapsack sprayers such as the Remo RM-SPL12A replace the hand lever with a small electric pump. Motor sprayers pair a petrol engine or electric motor with a larger pump, a tank or barrel, a hose reel and a spray gun or boom, and these are where a separate diaphragm pump such as the Shuangding MB4130 comes in.

Whichever size you buy, the same questions decide whether the sprayer puts the right amount of liquid on the crop: how much flow the pump gives at what pressure, which nozzles are fitted, how the user calibrates, and whether every wetted part resists the chemicals your customers use. Our garden and forestry machines list battery sprayers and spreaders, and the irrigation equipment section holds pumps, hoses and fittings.

Knapsack and battery sprayers

For a knapsack, ask for tank volume, empty and full weight, harness padding, lance length and material, and the nozzles supplied. Pressure control matters more than any other detail. Many backpack sprayers carry a regulator that holds pressure steady, which keeps the application rate consistent; hand sprayers without one rely on the user keeping a steady pumping rhythm [2]. Ask whether a regulator or pressure-control valve is fitted and at what setting.

For battery models, add battery voltage and capacity, charger time, pump pressure settings and run time with a stated nozzle. Zhejiang Remo Garden Machinery sells a 20 V cordless line, so ask whether the sprayer battery also fits its other tools, such as the Remo RM-US3A spreader. Customers who buy one battery tool often add more on the same pack.

Diaphragm pumps: flow, pressure and sizing

Diaphragm pumps belong to the displacement family with piston and roller pumps: each stroke moves a set volume, so output follows pump speed and stays nearly the same as pressure rises [1]. One extension table gives diaphragm pumps a working range of about 50 to 850 psi and 1 to 60 gallons per minute [1]. That high-pressure ability is why they suit orchard guns and long hoses.

Size the pump for the whole sprayer, not just the nozzles. The guidance is to add the nozzle flow, the flow needed for tank agitation and any strainer-flushing flow, then allow about 20 percent extra for pump wear [1]. For hydraulic agitation, a rule of thumb is a return flow equal to 5 to 10 percent of tank capacity [1]. Ask the factory for a flow-against-pressure table at the rated shaft speed, the speed and power the pump needs, the shaft and mounting type, and whether an air chamber is fitted to smooth pulses.

Because a displacement pump keeps pushing when the gun closes, the sprayer needs a pressure relief valve that sends excess flow back to the tank, rated for the system's maximum pressure [1]. Jinhua Shuangding Machinery supplies spray assemblies and diverters as well as pumps, so ask whether the relief and control unit is matched to the pump you order.

Engine choice follows from the pump's power demand. Engine makers such as Zhejiang Yaofeng Power Technology and Shaoxing Leapaq Power Machinery build general-purpose petrol engines; a water pump such as the Yaofeng YFHP20 is built for water transfer, while a diaphragm sprayer pump is built for chemicals.

Nozzles and strainers

Nozzles meter the flow and set droplet size. Catalogue flow figures are measured with water, and denser spray mixes change the flow at the same pressure [3]. Changing pressure also changes spray quality: in one worked example, lowering pressure moved a nozzle from a medium to a coarse spray and outside the label's requirement [3]. Orifices wear with use, which raises flow and distorts the pattern, so calibrate often [3]. Ask for a nozzle chart with each sprayer and a spare nozzle set in the carton. A garden hose nozzle is designed for watering and is a different product from a spray nozzle.

Strainers protect the pump and nozzles. Screens should get finer from the filler opening to the nozzle, and displacement pumps need a suction strainer of about 30 to 50 mesh [1]. Nozzles that need screens finer than 50 mesh tend to plug [1]. EU and UK machinery rules for pesticide application ask for nozzles, strainers and filters to be marked so their type and size can be identified [5].

Calibration your customers can repeat

A sprayer sells better when the manual shows how to calibrate it. A common extension method for backpack sprayers uses a test strip of one 128th of an acre: walk the strip at a steady pace, time it, then collect the nozzle output for that time; the fluid ounces collected equal gallons per acre [2]. If the result is more than 5 percent from the label rate, adjust and repeat; under 10 percent, adjust pressure, and beyond that, change the nozzle size [2]. Higher pressure raises the rate but makes more fine droplets that can drift [2]. Ask the factory to include a metric version of this procedure in the manual.

Machinery placed on the market for pesticide application must allow easy and accurate rate adjustment, prevent drips when spraying stops, empty completely and clean easily, and the instructions must cover calibration, compatible nozzles and filters, and replacement criteria for wear parts [5].

Chemical-resistant materials

Many pesticides corrode metal parts quickly, so the system should be flushed after use and the pesticide label checked for cleaning steps [1]. Ask what every wetted part is made of: tank, pump body, valves, seals, hoses and nozzles.

Diaphragms come in several rubbers. Kverneland describes nitrile as the standard membrane with medium chemical resistance, a polyurethane grade sold as Desmopan as good to very good, and Viton as very resistant to products that make rubber swell, at the cost of lower mechanical strength [4]. Ask which diaphragm and valve materials the pump uses as standard, which are available, and which products the maker lists as incompatible.

Hoses should resist chemicals, sunlight and oil; EVA and EPDM are named as chemically resistant, and suction lines need a reinforced hose that will not collapse, as large as the pump inlet [1]. A PVC suction hose suits water transfer; for chemicals, confirm the compound with the supplier, since some pesticides damage PVC [1]. The same check applies to PP couplings and a double-union ball valve on the filling line, and to lay-flat hose used to carry water to the mixing point.

Comparing quotes

Line up quotes on the same points: tank size, pump type and flow-pressure table, relief valve, nozzles supplied, strainer meshes, materials of every wetted part, battery or engine details, spare parts such as diaphragms, valves and seals, and the calibration section of the manual. For hillside orchards, ask how the sprayer will be carried; some growers move tanks on an orchard monorail transporter, and Ningbo Lihao Machinery builds these systems. Ask each supplier to confirm in writing which certificates name the exact model you are buying.

Source notes

[1] Virginia Cooperative Extension, Virginia Tech — Plumbing Systems of Agricultural Sprayers (publication 442-452) (2009) [2] NC State Extension — Calibrating a Backpack Sprayer (AG-576) (2000, revised 2024-01-02) [3] Ohio State University Extension (Ohioline) — Selecting the Best Nozzle for the Job (FABE-528) (2016-01-21) [4] Kverneland Group UK — Pump diaphragms: the right membrane for the job (2026-07-02) [5] legislation.gov.uk (UK Government) — The Supply of Machinery (Safety) (Amendment) Regulations 2011 (SI 2011/2157), Schedule: section 2.4 Machinery for pesticide application (implementing Directive 2009/127/EC) (2011)