Centrifugal Pumps Design and Application 2nd ed - Val S. Lobanoff, Robert R. Ross (Butterworth-Heinemann, 1992)

350 Centrifugal Pumps: Design and Application
Figure 16-9. Axial thrust on single-suction open impeller with ribs on back side.
Stacked Impellers. With all impellers facing in one direction, the area
between the last impeller and the high-pressure stuffing box is under full
discharge pressure. Pressure is broken down across a balance drum, with
the diameter of the drum sized for axial balance. Wear on the balance
drum will affect axial balance, therefore bearing rating should be sized
accordingly. On critical applications, particularly where a high rate of
erosion wear is anticipated, the permanent installation of load cells
should be considered.
The low-pressure side of the balance drum is piped back to suction, as
is the low-pressure side of the throttle bushing in the back-to-back ar-