Backpack sprayers

Backpack sprayers are standard equipment in most operations. They are convenient and well-suited for smaller application jobs, such as treating individual plants or small areas, spot-spraying weeds and for even larger jobs on terrain where other equipment can't go.

“These sprayers are ideal for those times when you need to apply products in confined places or when you need to be especially careful of your surroundings,” says Carol Dilger, corporate marketing services manager for Stens, an Ariens Company.

Small sprayers are available as pull-behind units, too. These hold larger quantities of spray but can be limited by access. Backpack sprayers, by contrast, can go wherever you can. On the other end of the size range, the smallest sprayers are the hand-held units. These are, of course, completely portable, but hold very small quantities of spray. Plus, they require two hands to pump (to maintain pressure), which means you can't spray and pump simultaneously. These do find use in the professional market, but are primarily intended for homeowner use.

Worth the weight?

Backpack sprayers are designed to be lightweight, for obvious reasons. How much your backpack sprayer will weigh depends heavily on its tank size. Depending on spray-tank capacity, most sprayers weigh anywhere from 15 to 45 pounds fully loaded, though some units go higher. Greater capacity is advantageous, but you must balance this with the usability of a heavier sprayer. Loads over 40 or 50 pounds can be strenuous for some people.

When designing tanks for backpack sprayers, manufacturers were faced with a dilemma: The tanks had to be lightweight, yet durable. The solution: polyethylene plastic. This material is resistant to corrosion from chemicals that you might use and it doesn't weigh much. It's the industry standard because other materials, perhaps durable, weigh too much to be considered for backpack use.

Most backpack sprayers have a spray-tank capacity of about 4 gallons. Some hold a little more, which will make them weigh slightly more (for every gallon of tank capacity, add about 8 pounds to the total weight of the sprayer). If you need even more capacity but still like the convenience of a backpack sprayer, consider purchasing an additional tank. It's an added expense, but can save you time when you're trying to finish a job. Also, an extra tank can come in handy when you want to spray more than one product without emptying the sprayer and starting over.

There is another reason to consider owning more than one tank: avoiding contamination. Some chemicals, notably broad-leaf herbicides, can be difficult to fully rinse from spray tanks due to their affinity for the plastic. Therefore, many operators have a sprayer that they never use for anything except herbicides, and another just for insecticides. This way, there is no chance of accidentally applying herbicide residues to a plant to which you are applying insecticides.

Pumped up

A manually powered backpack sprayer is equipped with a liquid-holding tank, pump and pumping lever, pressure-holding chamber, hose and wand with a control valve. It's important to understand that the liquid-holding tank is not pressurized. Each tank has a smaller, pressurizing chamber. Liquid is carried to the chamber by a pump. The pump works by drawing liquid from the sprayer's supply tank and sending it to the pressurizing chamber where seals and valves hold the liquid under pressure until you squeeze open the valve on the wand. Several pump types are available, but the two most common are piston and diaphragm pumps.

Hand pumps are typical, but some manufacturers also make engine-powered backpack sprayers. Expect these to weigh more than manual backpack sprayers. However, an engine eliminates the fatigue that can set in after hours of hand pumping, as well as maintaining consistency of pressure. Engine-powered pumps may use a rotary-type pump rather than the diaphragm or piston pump common on manual powered units.

The pressure's on

Relatively high pressures can be reached with backpack sprayers, although most operate at 15 to 95 psi. Be aware that on some units, pressure gradually decreases as the tank empties and spray is applied. If you are using your backpack sprayer to apply chemicals, you need to make sure that pressure remains constant and that enough flow reaches the nozzle at the desired pressure.

Some backpack sprayers feature built-in pressure regulators. For those that don't, consider installing a pressure-regulating valve or spray-management valve that regulates pressure. Also consider a pressure gauge if the sprayer is capable of accepting one. It aids uniform application, which partly depends on consistent pressure. Install it on the side of the tank where you see the shutoff valve. This way, the gauge will show tank pressure only when the valve is open.

Control the flow

Nozzles are one of the most important aspects of your backpack sprayer. They affect flow rate, the uniformity of application, coverage and amount of drift.

“The tips on most backpack sprayers are designed to allow you to interchange nozzles and select the one that best fits your current application needs,” says Chris Nordling, technical service representative for Shindaiwa. Be sure to have several available for a variety of application rates and patterns, rather than trying to use one nozzle to suit all your needs.

You tend to get what you pay for in nozzles. And because they are such a vital aspect of your backpack sprayer, the extra money for quality nozzles will be well worth it.

Get comfortable

As manufacturers become more aware of the need to increase operator comfort and ease, backpack sprayers are becoming more adaptable. Look for models that offer no-fuss clean up, are easy to fill up and use reversible pump handles that allow you to switch from right- to left-hand operation. Also make sure the model you purchase comes standard with adjustable shoulder harnesses that are softened by shoulder pads.

Who: Echo
What: MS-100
Description: Equipped with a 4.5-gallon polyethylene tank that is treated with UV-inhibitors for long life, the MS-100 backpack sprayer is designed for grounds maintenance, pest control, waterproofing and other jobs requiring the application of large amounts of liquid. Its diaphragm pump is durable and easy to use. The sprayer also features a 24-inch brass wand with an adjustable brass nozzle, a spray pistol with brass shut-off pin and double O-rings, and a built-in check valve in the cap to prevent the tank's ingredients from leaking. It produces up to 150 psi and comes with a 1-year commercial warranty.
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What: Commercial Plus
Description: Choose from a durable piston pump that provides a working pressure up to 90 psi with adjustable pressure-relief valve or a comparable diaphragm-pump model. Both feature a 4-gallon UV-stabilized polypropylene tank that resists sun, heat and chemicals; a 20-inch fiberglass spray wand; a high-impact composite trigger value; interchangeable pump handle for left or right-sided operation; fixed-fan and adjustable brass nozzles; and adjustable nylon shoulder harness with shoulder pad.
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Who: Robin Products Group
What: RS401
Description: The RS401 features a 37.7cc, 2-hp engine and weighs 18.7 pounds with a 34-ounce fuel tank that requires 25:1 fuel mixture. It has a 23.2-quart chemical tank, diaphragm carburetor, solid-state ignition and rotary-type pump with self-priming gravity-type system. It is 11.25 inches long, 15.75 inches wide and 25.75 inches tall, and has spray output of 3 quarts per minute at 327 psi. Standard accessories include spray head, tool kit and nozzle with control valve.
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Who: Shindaiwa
What: SP300 and SP415
Description: The SP300 backpack sprayer is designed to be light-weight and is for medium-duty use, while the SP415 can handle a more demanding schedule. Both are equipped with a tank and integral base constructed of high-density, UV-protected polyethylene that is chemical-resistant. The in-tank pump system minimizes the chance for leaks and features a built-in agitator that minimizes operator effort and promotes constant mixing. Padded shoulder straps reduce operator fatigue and do not absorb moisture. Reversible pump handle can be installed for right- or left-hand operation. Tank capacity is 3 gallons with 65 psi for the SP300 and 4 gallons with 90 psi for the SP415.
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Who: Solo
What: Model 425
Description: This 4-gallon sprayer features a piston pump, pressure gauge and adjustable brass nozzle. In addition, it has a fold-up handle and padded straps for comfortable handling. It provides high-impact strength while eliminating rust and corrosion, and features a molded-in, electrostatically powder-coated steel-tube frame and stand for added stability.
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Who: Stihl
What: SR420
Description: The SR420 features the Stihl IntelliCarb compensating carburetor, an innovation which allows for longer running times at full power without the need for constant air filter cleanings. A new heavy-duty filter system, which includes a vertical, pleated air filter, is almost self-cleaning. The gas tank is separate from the fan housing, which reduces the machine's vibration. The sprayer weighs 24 pounds with a container capacity of 3.7 gallons. It has a spray range of 38 feet vertically and 40 feet horizontally. It also features a swivel air tube for directional control, adjustable straps, built-in top handle and tool holder.
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