Variable-Concentration Direct Injection from Fixed-Ratio Diluent-Driven Pumps

An open-loop, variable-concentration, direct injection system for sprayers was developed by partitioning flow through parallel, fixed-ratio, diluent-driven (in-line) chemical pumps and a bypass branch. Due to the inherent, dual surging action of the motor and pump within the in-line unit, temporal fluctuations in pressure, flow, and chemical discharge were monitored since hydraulic atomization, nozzle pattern, and spray application uniformity may be affected. Test factors included flow partitioning through branches, flow rates, and pressure dampening. Results indicated preferential flow through some in-line units. Flow rates differed between in-line units by up to a factor of 4.58 for two in-line units, and up to 10.2 for two units and the bypass. As a baseline measurement, the bypass operating alone had pressure fluctuations up to a CV of 2.6%, which may have been due to the pressure relief valve and/or the throttling valve. However, the bypass tended to dampen flow and pressure fluctuations introduced by in-line units. Single in-line units and dual in-line units usually increased upstream and downstream pressure fluctuations. The CV in pressure ranged from 1.4% to 18.2% for single units and from 5.8% to 32.4% for dual units. Increased flow rates through in-line units and increased hose lengths downstream from in-line units generally resulted in dampened pressure fluctuations. Increased flow rate, and a corresponding increase in the oscillation speed of the motor and pump plungers of the in-line unit, decreased injection tracer concentration errors. The CV in injection tracer concentration ranged from 1.3% to 14.5%, and metering error ranged from -44% to +57%, which were comparable with other reported systems. It was concluded that highly accurate, variable-concentration direct injection may require a closed-loop control of chemical inputs and diluent flow modulation through the system branches.