Page 382 - Centrifugal Pumps 2E

Shaft Design and Axial Thrust 347

Figure 16-6. Axial thrust on single-suction closed impellers with no rings on
back side.

Semi-open impellers. Depending on level of thrust, semi-open impel-
lers can be designed with or without back ribs. Pumps of this type are
quite often troublesome and inefficient. The gap between the open vane
and liner must be carefully controlled at assembly, as any increase in this
gap will affect the head developed by the pump. The problem is com-
pounded when the back rib is added, as gaps on each side of the impeller
must be controlled. Methods for calculating axial thrust are shown in
Figures 16-8 and 16-9.

Multi-Stage Pumps

Axial thrust becomes more important with multi-stage pumps, because
of the higher developed pressure and combined thrust of several stages.
Impeller arrangement will normally be back to back for volute-type