They are often used when spraying surface weeds with a handgun. Applicators may find that the output from their sprayer will diminish greatly when spraying with 1 to 2 percent polymer. The reason often given for the flow reduction is that the water-polymer mixture flows less readily, and the pump is unable to force the material through the nozzles, however, this is not the reason for the reduced flow. Positive displacement pumps normally used in aquatic weed spraying have the capability to force any amount of material that enters the pump out of the pump. The difference is that the pressure required to force the viscous liquid through the discharge hose would have to be greater.
More pressure means the engine has to deliver more horsepower.
Output reduces when using these high concentrations of polymer because the amount entering the pump suction is reduced. Flow rates of water and water-polymer mixture through a given nozzle at a given pressure vary little. Most of the flow reduction is because the pump is starved on the suction side. Centrifugal spreaders can treat a wide swath when relatively large granules are used. The rotor that slings the granules is driven by a 12-volt DC motor.