Clearance gap width
The clearance gap width usually refers to the distance between the stationary and rotating component of controlled gap seals.
In centrifugal pump engineering, the clearance gap width has a special significance for open axial and mixed flow impellers. In these impellers, it represents the clearance between vane tip and casing wall and has a considerable influence on the pump's performance data. On axial impellers, the clearance gap width is usually designed to be 1 o/oo of the impeller diameter, with a minimum of 0.1 mm.
Much larger clearance gap widths must be provided in the case of temperature fluctuations of the fluid handled and of the centrifugal pump itself during the start-up process to account for the varying heat expansion characteristics of different pump components.
The sizing of the clearance gap width is dependent on the type of bearings, the permissible extent of clearance gap cavitation and the extent and nature of contamination of the fluid handled (see Solids transport).