The transition processes of the centrifugal pump in hydro accumulation power plant (HAPP) are studied in the article. The reliability of the pumping system is increased by the correct selection of the parameters of the transition process when regulating the operation of the pumping units. This prevents vibration damage and erosion. Based on the results obtained by calculating the hydraulic shock and the pressure loss in the system together, damage and failures in the pumping equipment and the network can be avoided. The results and graphs allow you to choose the right electric motor for the pump unit, taking into account the required pressure and water supply. Technical and economic efficiency is achieved by choosing a rated electric motor for the pump unit. Constructing graphic descriptions of the pump, determined the magnitude of the hydraulic effect in the grapho-analytical method.