Some wear or erosion will occur at the point where the impeller and the pump casing
Figure 10 Centrifugal Pump Components
nearly come into contact. This wear is due to the erosion caused by liquid leaking
through this tight clearance and other causes. As wear occurs, the clearances become
larger and the rate of leakage increases.
Eventually, the leakage could become
unacceptably large and maintenance would be required on the pump.
To minimize the cost of pump maintenance, many centrifugal pumps are designed with
wearing rings. Wearing rings are replaceable rings that are attached to the impeller and/or
the pump casing to allow a small running clearance between the impeller and the pump
casing without causing wear of the actual impeller or pump casing material. These
wearing rings are designed to be replaced periodically during the life of a pump and
prevent the more costly replacement of the impeller or the casing.