Check valves are used in various industries to prevent reverse flow in pipelines and thus protect sensitive components such as pumps or to prevent accidental discharge of the container. An ideal non-return valve closes when the flow changes direction. Since reverse flow often occurs in real situations, water hammer occurs at the time of closing. This pressure wave influences the valve and the pipeline equally. The amplitude of such pressure wave speed is determined by the return flow at the time of closing. Unsteady fluid flow is often simulated using one-dimensional codes. These codes are very quick, but, because of simplification, contain inaccuracies that should be taken into account. With the current state of technology, CFD analysis in three dimensions is not a problem, but such simulations are significantly more time consuming and computationally demanding than traditional methods. In this paper, the closing process of a swing check valve during transient flow is modeled. The reference model is the swing check valve type V2-08, DN 300, from valve manufacturer MIV d.d. The result of such a numerical model is the closing characteristics which shows the change in the angle of openness in relation to the average deceleration of flow. After that the model of the non-return valve, with a known closing characteristics, is placed into two characteristic pipelines. Method of characteristics is then used to calculate pressure transients in these pipelines.