When pressure head of one point of pipeline drops to saturated vapor pressure head in water hammer, column separation occurs. Occurrence of column separation might result in some damages in pipeline or other equipment in the system. In discrete vapor cavity model as the solving model, cavities could form in any computational grid specifically in high elevated regions of pipeline. In this study the numerical results are compared with the experimental data and shown having a good agreement together. Moreover, the effects of pipe diameter, flywheel effect, and pump specific speed on transient flow behavior are investigated. It is shown that pressure head for pumps with higher specific speed and inertia have a lower peak amount.