Stiffness Ratio

A design value used to evaluate the relative stiffness of a pump shaft in a single-stage centrifugal pump with an overhung impeller. The ratio is the length of the shaft cubed (L³) divided by the shaft diameter to the fourth power (D⁴). The stiffness ratio should fall below 60 when using inches and below 2.0 when using millimeters to avoid excessive shaft bending and deflection. Stiffness ratio is another name for the L³/D⁴ ratio as applied to single-stage centrifugal pumps with an overhung impeller.

Also known as Slenderness Ratio.