Design, construction and testing of a wheel driven crop sprayer

Abstract

Ugandan farmers are currently using lever operated backpack sprayers that consist of a 10 -20 L capacity tank carried by two adjustable straps. The purpose of this project was to design, construct and test a wheel driven crop sprayer that applies chemicals adequately at the rate stated by the manufacturer on the packaging with limited wastage, has increased capacity and less drudgery. The sprayer components were designed using empirical formulas and principles of mechanics and were modelled using computer software known as Solid Edge. The knapsack sprayers require constant pumping to develop the adequate pressure which is time consuming and very small area is covered while spraying so more time is required to spray. The discharge rate depends on the speed of pumping and the rate of application to the crops depends on the walking speed of the operator so therefore to ensure coverage of the crops, the operator should spray at a low speed. The wheel driven crop sprayer was designed with a capacity of 32 L and nozzle triggers that turn the flow on and off as required by the operator hence reducing the wastage of chemicals encountered during turns. The performance of the wheel driven crop sprayer was tested and evaluated and it was ascertained to have a mean working speed of 0.774 m/s, mean discharge rate of 0.0124 L/𝑠, application rate of 0.032 L per 𝑚2 and a spraying efficiency of 81%. The rate of application from the sprayer depends on the speed of operation. The optimum speed the machine should be operated at ranges from 2-3 mph (0.9-1.3 m/s) which is the average normal walking speed of a person. In conclusion, the designed machine is appropriate for use by a farmers with an acreage of 1-2 acres since the sprayer is designed for small scale farmers.