The study of transitory phenomena in hydraulic systems is present in several branches of the engineering, in the hydroelectric power stations area and in the petroleum industry. The present work introduce a comparative analysis of this phenomenon using three approaches of distinct modeling: the classic characteristics method, the technique of bond graphs and the treatment through the power flow. In the case of characteristics method is used the procedure proposed by Streeter. In the modeling through bond graphs is adopted the generalized analogy among the fluid, mechanic and electric systems. In the representation by power flow modules previously developed are coupled considering the cause and effect relationships between components of one system. All methods were implemented in Matlab and were tested and compared from simulations in two simple systems composed of a reservoir, fluid lines and valve. The results obtained through the methodology of power flow are near of the discoveries by the traditional approaches.