For creating new mesh with snappyHexMesh it is recommended to create new OpenFOAM test case just with system and constant directory. Go to your user directory and create directories for rotor region mesh. It is recommended to copy a similar tutorial case and modify just the different parts of the case.
The input .STL files are located in constant/triSurface and can be directly viewed in paraview.
# paraview Seven .STL files are presented, namely:
pump_impeller_outlet.stl
pump_impeller_shroud.stl
pump_inlet_pipe.stl
pump_rs_connection.stl
pump_impeller_blades.stl
pump_impeller_hub.stl
pump_spiral.stl
Interface between rotor and stator part is defined by imposed cylinder pump_impeller_outlet.stl file.