One of the major problem in an injection-type agricultural sprayer is measuring and controlling the flow rate of the concentrated chemicals. An electro-mechanical feedback system was designed to control the chemical concentrate flow rate in an injection-type sprayer. The system works well for a fluid with viscosity from 90 to 300 mPa.s and a flow rate from 3 to 20 mL/s (0.1 to 0.68 oz/s). A linear relationship was achieved between the flow rate and metering pump speed. The system also showed a good dynamic performance.