The ALBA Synchrotron Light Source cooling system is submitted to regular pump start-ups and shut-downs. Moreover, pumps can trip due to motor power failures. As a result, the piping system can be subjected to surges and pressure oscillations. The 1D thermo-fluid simulation software Flowmaster¿ has been used to predict these transient conditions taking into account the fluid compressibility, the pipe elasticity, the characteristic time response of the check valves and the pump/motors moments of inertia. During pump start-ups, significant pressure rises are detected that can be reduced by readjusting the PID controller parameters. Unexpected pump shutdowns do not appear to provoke significant water hammer conditions. However, pressure fluctuations are generated mainly in the same pumping line but also in the rest of the system due to the particular common return configuration. In all the cases the pressure regulation mechanisms acting on the pump rotating speeds serve to attenuate the consequences of these transients. Finally, the feasibility of the model to simulate the effect on the system response of trapped air inside the pipes has also been evaluated.