PUMPS_proof 23/08/2016 15:18 Page 1
PUMPS
Pump performance
John Chadwick looks at
trends and new
technologies in pumps
ining offers challenges in selecting the
proper pump due to the demands of
the environment and the nature of the
material pumped. Rick Kesler, a Sales Manager
for ABEL Pumps, suggests some considerations
for making such a selection: “Mining slurries
tend to be abrasive with solid specific gravities
of 2.65 or more and slurry specific gravities of
1.65 or greater at solids concentrations as high
as 70%. Abrasive wear varies with velocity.
Consideration should be taken in pump
selection to allow for the effects of abrasive
wear.
“Centrifugal pumps can have the lowest
capital cost. However, velocities are high and
special materials need to be selected when
choosing the proper centrifugal pump.
“An alternative is offered by Positive
Displacement pumps (PD pumps) which operate
at slower speeds and are very effective in the
transport of mineral slurries.” Progressive cavity
and rotary lobe designs are popular in industry;
but, the path of the slurry goes through some
tight places; rotors and stators or lobes. “These
designs are unfavorable to abrasive wear in the
more intense applications and should never be
run dry.
“One of the best pump options for this duty
are Piston-Diaphragm designs which can run dry
and are highly abrasive resilient. Slurry does not
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108 International Mining | SEPTEMBER 2016
pass through tight constrictions. Instead,
elastomer diaphragms are employed and are
relatively passive in displacing the slurry. Thus
fatigue limit of the diaphragm determines the
diaphragm life and not so much abrasion.”
Factors in the selection of a mining pump
should include flow rate, pressure, particle size,
percent solids of the slurry, abrasiveness, and
more.
“Centrifugal pumps operate along a
pressure/flow curve with a best efficiency point
in the centre part of the curve. This efficiency
may be 75% or higher at the best efficiency
point (BEP). Steady operation near the best
efficiency point is desirable. Variable flow rates
can induce cavitation or recirculation on either
end of the performance curve. These pumps
often require gland seal water to operate. The
pumps often operate at speeds of 1,200 rpm or
1,800 rpm so abrasive wear is enhanced.
Centrifugal pumps generally have higher solids
size capability than most positive displacement
designs.
“If total dynamic head, abrasiveness, and
variability of flow limit the usefulness of
centrifugal pumps, positive displacement pumps
may offer a better solution.
Up to about 7 bar, rotary lobe pumps can be
used, and up to a 14 bar or more progressive
cavity pumps are functional. Again, these pumps
The Weir Minerals booth at MINExpo will
feature much pump news, see the preview
article in this issue
should not be run dry. The more abrasive
slurries may inflict rapid wear of rotating
components. Piston diaphragm designs offer dry
running capability and will not suffer near the
adverse effects of abrasive wear. Efficiencies are
higher with these designs although capital costs
are generally more.”
Piston diaphragm pump design is, he says,
the preferred method of pumping slurries at
high pressures and flows up to around 130
litres/s.
“Some applications such as mine dewatering
allow a choice between staging centrifugal
pumps and use of a high pressure positive
displacement pumps, which can accomplish the
pumping task in one stage. Lowest initial capital
cost favours the staged centrifugal pumps in
most cases. However, other factors enter into
the decision. These factors include wear,
maintenance, efficiencies, use of gland seal
water, placement of centrifugal stages and
more.
“Wear is a consideration in high pressure
slurry pumping. Velocities of centrifugal pump
impellers accelerate wear compared to the
slower stroke rates of positive displacement