Transiente hidráulico em adutoras: estudo de um sistema adutor em operação em Porto Ferreira-SP

Abstract

The hydraulic transient is a phenomenon that occurs when a sudden change in the behavior of a certain fluid is imposed, either by changes in route (a valve closing, for example) or changes in physical parameters such as the pressure. Known as water hammer, the effect is the unbalance of particles observed through a shock wave composed of very high pressures followed by very low pressures in a cyclic manner and in a short period of time. The results range from pipe wear to breakage. The phenomenon is a serious operational risk for water supply systems, as it causes losses of water, energy, environmental impact, risk of contamination and, when it occurs in highly critical pipes for a system, discontinuity of supply. Therefore, It is essential to verify the occurrence of the phenomenon and contain it. This work performed the diagnosis and prognosis of a pumping pipeline system in real operation consisting of two centrifugal pumps in series and two connected pipelines, one in DN350 cast iron and the other in DN250 and DN400 PVC DEFoFo, where the latter is equipped with a relief valve and a triple function suction cup. The diagnosis, performed through the characterization of the system and the hydraulic transient modeling in the software Allievi, simulating scenarios of stoppages of the booster pumps, revealed maximum pressures on average 35% above the capacity of the pipes, reaching about 135mca (while the steady state works on average with 70mca) and negative minimums of -10mca (vacuum), indicating the occurrence of cavitation in practically the entire system. The devices already installed, despite having their contribution, are not sufficient to control the transient, therefore, it is proposed to install two closed surge tanks with a capacity of 4m³ each, close to the output of the booster pumps pipes . The simulation with the tanks presents results consistent with the literature and demonstrates control of pressures during the transient, where the maximum points are close to the regular level of the steady state and the minimum pressures become positive and completely far from the cavitation limit.