Does the pump impeller need to be rebalanced after a certain time period?
High unbalance of a rotating component such as an impeller may result in unacceptable vibration. Pump impellers are typically balanced in accordance with ISO 1940 balance quality grade G6.3 or better. An impeller balanced for clear-liquid service is expected to remain substantially in balance for most of its operating life, unless it becomes clogged with a foreign object or fails mechanically for some reason.
Therefore, rebalancing is typically not required unless a specific vibration issue occurs that can be specifically tied to impeller balance.
However, slurry pump impellers are subject to wear in-service and will naturally begin to change their balance due to the erosion of metal along the wear surfaces. Consequently, bearings and shafts in a slurry pump are to be designed for a large amount of unbalance in the impeller. Slurry pump impellers may be balanced to a lesser standard (higher residual unbalance) than a clear-liquid impeller.
The levels of residual unbalance allowed are determined by the manufacturer and are based on a number of operational and design factors. Therefore, it is not necessary for the consumer to make any balance changes themselves. As a rule of thumb, slurry pump impeller balance requirements will fall between balance quality grade G40 on the high (large amount of residual unbalance) side and grade G6.3 on the low (small amount of residual unbalance) side.
For more information on pumping froth and slurry materials or impeller balance, refer to ANSI/HI standard 12.1-12.6 Rotodynamic Centrifugal Slurry Pumps at pumps.org.