Reversible pump turbine (RPT)'s runner inter-blade flow unsteadiness onset and development especially under off-design conditions is still one of unresolved issues, yet continues to cause different complications on a daily basis within pumped storage power plants, detrimental pressure pulsations and resulting structural vibrations among others. Though different methods have been used to solve the issue at hand, an adequate solution suitable for all designs has not yet been found; a fact that calls for a more deep understanding in terms of RPT runner flow dynamics and possible influencing parameters. Therefore, the present study seeks to investigate the RPT flow dynamics and associated runner inlet pressure pulsations under off-design operating conditions, as well as the effect of runner blade number on the same. Three RPT models with different runner blade numbers were numerically investigated. The results showed that runner flow unsteadiness has a close relationship with the machine flow conditions, where flow vortices are mostly located at the runner shroud and vicinities. The runner flow unsteadiness decreased with the increasing blade number. The runner blade number considerably influenced runner inlet pressure pulsations where pulsation levels of models with 9 and 10 blades were the highest and lowest respectively. (c) 2020 Elsevier Ltd. All rights reserved.