Page 261 - Centrifugal Pumps Design and Application

234 Centrifugal Pumps: Design and Application

Table 13-3
Pump Selection Guide for Wear Resistance
Abrasion Class Nature of Slurry Selection
Mildly abrasive Concentrations of relatively Cast iron construction usually
soft solids or very low con- satisfactory, but hard- faced
centrations (measured as impeller rings and special at-
ppm) of hard silt-sized par- tention to stuffing box area is
ticles. justified. Consider stainless
steel impeller. No limits on
pump speed.
Abrasive Low concentrations of hard Slurry pump design required
fines or high concentrations with Ni-hard, chrome iron, or
of soft material. rubber construction. Open im-
pellers are acceptable. Al-
though no limits are placed on
pump speed, discretion is ad-
vised.
Severely abrasive High concentrations of hard Slurry pump design required
fines or lower concentra- with chrome iron construc-
tions of coarse material. tion. Restrictions are placed
on allowable pump speed and
total head.
Primary circuit Maximum concentrations of Severe-duty slurry pump de-
fines or coarse material up sign required with chrome
to 10 mm usually. iron construction. Large re-
strictions placed on allowable
pump speed and total head.
Parts life is measured in
months.
Dredge Large concentrations of Dredge type design required
boulder-sized solids. with manganese steel con-
struction to resist impact, \fery
low rotational speed required,

Areas of Wear
Casing

The rate of wear and the hydraulic forces within the pump will be re-
duced if concentric-type casing volutes are adopted over conventional
spiral volutes. At "off" design point operation, the static pressure around
the impeller's outside diameter will be relatively uniform, and turbulence
in the vicinity of the cutwater will be effectively reduced as will the
slurry velocity entering the casing throat. Recirculation flows from the