vector is aligned with the blades under said optimum flow conditions fig5 shows a sectional view of the inlet guide vanes being fully inserted into the inlet flow as indicated by the broken line 5 5 shown on fig2 fig7 shows a typical vector diagram associated with flow conditions shown on fig5 where there was a substantial decrease in fluid flow rate as compared to the previously described optimum flow condition the axial inlet flow velocity being substantially lower than that at the optimum flow conditions is being represented by the vector v 39 while at the same time the blades rotational velocity as represented by the tangential velocity vector u has remained substantially constant as it will be described later such a low flow condition has called upon insertion of guide vanes 23 resulting in a change in the inlet flow direction from purely axial to a flow rotated to a angle a relative to the axis with the absolute inlet flow velocity represented bu the vector v to those skilled in the art it becomes obvious that such flow prerotation under certain low flow conditions and when the guide vanes inlet angles are designed properly will result in the angle b between the relative velocity vector w and the rotating axis direction shown on fig7 to coincide with the blades inlet angle b as shown on fig5 thus providing for a incidence angle free improved inlet flow conditions due to variation of the impeller blades tangential velocity along the impeller blades radius the guide vanes 23 as shown on fig1 and 11 may be configured to generally provide.