An iris mechanism for variable rate sprinkler irrigation

Variable rate irrigation intends to supply water at the right time and place in order to improve water-use efficiency, save energy and decrease nutrient leaching. The concept of an adjustable orifice sprinkler using an iris mechanism actuated by a stepper motor for use in variable rate irrigation was proposed and developed. A prototype was manufactured using additive manufacturing techniques. Its operational characteristics were evaluated. To predict the flow rate, a deterministic model that represented the operation of the sprinkler was proposed and validated. The observed discharge coefficients varied according to the operating conditions, these being: 0.530 when the orifice was fully opened; and an average of 0.636 when the iris mechanism reduced the orifice section. For the condition of a partially opened orifice, the phenomenon of jet inversion occurred causing the jet to become asymmetrical. The proposed concept allows flowrates closer to the required values to be obtained and consequently provides greater flexibility and accuracy to applying the target irrigation depth.