Page 375 - Centrifugal Pumps 2E

340 Centrifugal Pumps: Design and Application

Figure 16-2. Schematic representation of horizontal overhung pump.

Shaft Deflection

Shaft deflection calculations are usually performed on single-stage
overhung pumps to establish a relative measure of shaft stiffness. Deflec-
tion calculations are also performed on horizontal multi-stage pumps
when the potential of galling at wear ring or sleeves exists during start-up
or coastdown. The calculation for single-stage overhung pumps assumes
that the loading on the shaft consists of weight (for a horizontal pump)
and the dynamic radial thrust due to the pump hydraulics.
Figure 16-2 schematically represents a typical horizontal overhung
pump (Figure 16-3). The deflection at any point along the shaft between
the impeller and the radial bearing can be calculated from the following
equation.

This equation does not account for any support the shaft might receive
from the hydrostatic stiffness at the impeller wear rings and shaft throttle