The balancing device on centrifugal pumps is designed to fully or partially compensate axial thrust generated by the pump rotor. Designs incorporating a single balance drum or double drum require a thrust bearing to absorb the residual thrust.
If the balancing device consists of a balance disc, the entire axial thrust of the pump rotor is usually balanced. In this case, an additional thrust bearing is not required.
When the pump is in operation, the balancing device requires a certain amount of balancing flow through the clearance gap between the balancing device's rotating and non-rotating parts. The balance flow is subjected to considerable throttling on its way through the gap (see Pressure loss).
This pressure loss results in an axial force acting upon the balancing device which counteracts the impeller's axial thrust and effects the required balancing. Balancing devices are used when the axial thrust involved is extremely high, as is the case with super-pressure pumps.