The circumferential speed (u) is the velocity of a point particle performing a circular motion. This can be a point particle of a rotating pump shaft or a rotating impeller. The following relationship exists between the radius (r) of the point particle and the angular velocity (ω):
u = r • ω
The circumferential speed at relevant locations of the impeller has a marked influence on the suction characteristics, noise development and strength of the rotating components of centrifugal pumps.
Typical circumferential speeds (at the impeller outlet) range between 20 and 60 m /s, in exceptional cases up to 140 m /s.