Performance evaluation of injection metering systems

Abstract

A method for measuring the performance of agricultural injection metering systems was developed and used to assess the characteristics of three commercial system designs. Steady-state characteristics were measured using both colored dyes and salt as tracers. Dynamic response characteristics were determined by measuring salt concentration downstream of the injection point by monitoring electrical conductivity of the spray solution. Salt added to a viscous test liquid changed viscosity slightly only at low shear rates and it is concluded that this liquid is appropriate for use in evaluation tests with injection systems. Results from tests with 2 systems specifically designed for operation with agricultural sprayers gave a linear response with both water and the viscous test liquids and no evidence of dose pulsation in the delivered spray liquid. A system using a single-acting water driven piston had a performance that was dependent upon viscosity and that gave substantial dose pulsation. When injecting on the pressure side of the pump, response times for both increasing and decreasing dose levels were in the order of 3.2 s. When injecting on the input side of the pump, response times were greater and very dependant upon the total flow rate of the delivery system.