Figure shows the pressure distribution at the midspan of the casing at part load condition - at a mass flow rate which is smaller as the design mass flow rate.

The asymmetric shape of the volute results in a circumferential distortion of the flow conditions at the inlet of the casing. This distortion is especially pronounced at off-design points. The circumferential non-uniformity of the pressure field causes unbalanced radial forces that must be considered by designing rotor-bearing systems.