Variations in diameter and head loss were evaluated for low density polyethylene tubes (nominal diameters DN12 and DN20) submitted to operating pressures of 50, 100, 150, 200, 250, 300, 350 and 400 kPa. The diameters were measured with a digital paquimeter, its alterations by two dendrometers connected to a datalogger and the head losses with a differential pressure transducer. The influences of the operating pressure on the internal diameters, as well as on the head loss, especially for the DN20 tube were verified. Equations correlating flow and head loss were adjusted for each pressure level, additionally an equation obtained for all pairs of values, considering each tube model. The equations were compared by t test and it was observed that a single equation did not represent the head loss for all pressure levels tested, at 5% level of probability. Thus, other equations in which the head loss was expressed as a function of flow and diameter or flow and pressure were adjusted for each of the diameters.
irrigation; drip irrigation; polyethylene pipes
