Chapter 7 - The importance of running clearances in centrifugal pumps

Abstract

Running clearance in centrifugal pumps is done to achieve acceptable pump efficiency. This chapter presents the case of a single-stage overhung pump with a semi-open impeller, which has back pump-out vanes; a single-stage overhung pump with a fully enclosed impeller with shrouds back and front of the vanes; and a single-stage overhung pump of either semi-open or fully enclosed impeller design. The areas affected include hydraulic performance, energy consumption, reliability, and maintenance costs. These areas reflect the more common effects of running clearances in conventional designs of centrifugal pumps. Specific applications involving high energy or high speed centrifugal pumps often require even closer adherence to recommended tolerances. Materials with galling tendencies often require greater running clearances, as even a minor rub can cause a major failure with such materials. Further, optimized centrifugal pump application demands close attention to pump internal running clearances as one of the key elements in an excellent maintenance program.