The plastics industry and its derivatives, with the help of engineering have improved the quality of materials used for manufacturing pipes, mainly polyethylene. The elasticity of polyethylene tubes allows diameter increases as pressure rises, which is not taken into account by the mathematical equations used to determine the head loss. The purpose of this research was to quantify the errors on head loss determining in elastic tubes as a function of inlet pressure on the lateral line, comparing observed and estimated values by equations recommended in the technical literature. Three samples of polyethylene pipe were evaluated under 9 inlet pressures and 3 flow rate conditions, which corresponds to velocities of 1.0, 1.5 and 2.0 m s-1. Measurements for determining the outside diameter of the tubes were carried out under pressures from 0 to 588.4 kPa incrementing 49.05 kPa each step. For all evaluated conditions it was verified that pressure affects the continuous head loss in elastic tubes and the equations of Darcy-Weisbach, Hazen-Williams, and Flamant overestimate the results.
continuous head loss; microirrigation; polyethylene tubes
