Sprayers for on-road transport

Using a sprayer on a job site is one thing. Getting the sprayer to the job site is another. If you need to haul your spraying equipment from site to site, you're going to need a unit that's suitable for on-road transport.

There are several kinds to choose from: units on skids that mount on the back of a truck; units that are installed directly on the flatbed of a truck; units that mount on trailers, and trucks dedicated solely as a sprayer.

The type of sprayer you choose depends, as most equipment decisions do, on the specific jobs you need to carry out.

What kind of tank? Sprayers are usually made of fiberglass, plastic or stainless steel. Steel tanks can last for years and are durable enough for mechanical agitation, but they are less common than they were years ago.

Fiberglass tanks are more common and durable enough for mechanical agitation. Plastic tanks typically are not sturdy enough for mechanical agitation, says Scott Allen of Westheffer Co. in Lawrence, Kan. For businesses that want to display their names on their equipment, fiberglass and stainless steel tanks can be painted or have a decal place on them, while that's not usually possible with plastic tanks, adds Allen.

The size of the tank you need depends on the kind of work you are doing and how you transport the sprayer. Tanks can be as small as a few gallons or as large as 500or more.

Some spraying units are too big to safely transport on a pickup truck, and you'll want to choose a smaller tank. In other cases, you'll have to travel significant distances from job to job and won't want to return to your home base to refill your tank. Then you'll want a larger tank.

You should also determine the rate at which you'll be applying the spray on your job, says Allen. A job that calls for spraying 2 gallons a minute will empty its tank twice as quickly as one used on a job that calls for a spray of 1 gallon a minute.

The right pump Sprayer pumps generally fall into two categories: positive displacement and non-positive displacement. Roller, piston and diaphragm pumps are positive displacement pumps-that means the flow from the pump is directly proportional to the pump speed.

Roller pumps are the least expensive type of pump, says Ralph Menning of Hydro Turf Inc. in Mendota, Minn. Rollers revolve inside the pump housing and force the spray out to the nozzle. They are not considered a good choice if you are using wettable powder for spraying. The abrasive material wears down the rollers and diminishes the unit's effectiveness.

Piston pumps propel liquid by a piston moving in a cylinder. The intake stroke draws liquid in through one valve and the output stroke forces the liquid through another valve. Piston pumps can develop high pressure, but often their capacity is relatively low.

Diaphragm pumps are the most common type, says Allen. "Upwards of 80 percent of the pumps out there are diaphragm pumps," he says. A diaphragm connects to a piston, and as the piston moves, suction draws liquid through an inlet valve by moving the diaphragm. The piston's return forces and diaphragm inward and propels the liquid out. These kinds of pumps require less maintenance because there is less contact between the spray solution and moving parts.

A centrifugal pump is a non-positive displacement pump. Liquid enters the pump through the center of a rotating impeller. The spray is forced to the outer edge of the housing and delivered to the nozzle. These pumps can last a long time and produce a high flow volume.

Don't settle The spray solution in your tank has to be agitated to keep it from settling in the corners and bottom of the tank. Sprayers use either hydraulic agitation-also known as jet agitation-or mechanical agitation.

Hydraulic agitation uses part of the pump's flow to create a mixing action in the tank so the chemicals stays suspended in the spray mix. This is used especially with plastic tanks that are less suited to mechanical agitation. Mechanical agitation, considered more effective, requires a tank durable enough to support the weight of the mechanical agitators and the force they create. Paddles or propellers at the bottom of the tank stir the spray mix and keep suspended particles from settling.

Accessories Sprayers can come with an assortment of accessories, including a variety of nozzle and hoses, electrical or manual hose reels and spray guns.

Menning recommends sprayers that have a chemical injection system. This allows you to apply chemicals with exact application rates and eliminates over-application. Chemical injection units precisely meter pesticides and inject them directly into the plumbing so that the main tank holds only water. These units usually adjust to varying ground speeds and application volumes, so that rates "on the ground" remain accurate.

"If you have that, you could have anybody on the machine and still be sure that you're getting your material where you need it to be," says Menning.

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