Page 275 - Centrifugal Pumps Design and Application

244 Centrifugal Pumps: Design and Application

Figure 13-11. (A) Typical performance characteristic of nonsettling slurries; |B)
typical performance characteristic of settling slurries.

go over 100% in badly controlled systems. For this reason large margins
are built into the design of slurry pumps and motors. Usually the motor is
mounted above the pump on an adjustable frame (belt adjustment) to save
space and to safeguard against flooding. (Refer to Figure 13-10.)

The Effect of Slurries on Pump Performance

When centrifugal pumps are required to handle slurries, it is standard
practice to publish pump performance curves based on clear water per-
formance. Therefore, to predict the performance of pumps handling slur-
ries of different characteristics, correction factors are applied.
When handling slurries, the pump performance is mainly affected by
the solid particle diameter, specific gravity, and concentration. Very fine
particles in a slurry can be "nonsettling" and cause it to behave as a ho-
mogeneous Newtonian liquid with an "apparent" viscosity. Slurries with
very fine solids in suspension (usually less than 100 microns) will retain
liquid-like characteristics at volumetric concentrations very near to the
limiting voidage, and limits are related only to the effects of high viscos-
ity. Figure 13-1 la shows typical nonsettling slurry pump characteristics.