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Pump systems, pipes, valves and seals
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10
Mechanical Technology — June 2016
S
lurry pumps include various
types of heavy-duty centrifugal
pumps used for the hydraulic
transportation of solids. “Slurry
pumping involves a varied portfolio,
depending on the media being pumped,
but slurry pumps are almost always de-
signed and chosen based on their wear
performance,” begins Sedgwick.
The Metso slurry pump range covers
the pumping of any type of materials,
primarily ground rock, including large
particles using dredge pumps that can
handle particles of over 150 mm. “The
typical discharge from the mill in a
minerals processing application is in the
100
µ
m to 250
µ
m average particle size
range, combined with large rocks and a
steel content caused by mining activity
and broken mill balls (scats), which are
all pumped as very dense slurries that
cause high wear rates on the pump’s
internal components,” he explains
“Metso can offer the full range of
duties and wear lining options, from
rubber-lined to high chrome white cast
iron, but to get the best value, the pump
has to be well suited to the slurry it is
pumping,” he adds.
Showing a summary diagram of the
slurry pump range, Sedgwick says
that Metso’s approach to han-
dling the diversity of differ-
ent slurry types starts with
the American Hydraulic
Institute’s wear cat-
egory classification.
“For a Category 4
slurry, for example,
we recommend an
impeller aspect ratio
of 3. This is the ratio
between the pump’s
outside diameter and
Fit-for-purpose slurry
pumping
and lowest TCOs
Designed from its
inception for mill circuit
applications, the Metso
MD series MDM hard metal
and MDR rubber lined slurry
pumps offer sustained performance
with maximum time between mill
shutdowns.
Metso’s slurry pump selection chart and its pump selector software, Pumpdim, use the aspect
ratio as the primary variable in organising its range for different slurry requirements.
Using the flagship MD range of slurry pumps as an example, Metso’s Europe, Middle
East and Africa director for mining flow control, Steve Sedgwick talks about Metso’s
approach to slurry pump design and the key features that enable the company to
offer the lowest possible total costs of ownership.
the internal impeller diameter at the eye
of the impeller – OD/ID. Our flagship
MD pump is designed to meet these
extremely abrasive Category 4 needs,”
he tells
MechTech
.
The aspect ratio is a simple number
that sets the basic design limitation for
any centrifugal pump subjected to wear.
If the aspect ratio is large, then the size of
the pump has to be made larger to accom-
modate the larger impeller. This allows
the impeller to rotate at a slower speed
for the duty required, and it increases the
impeller vane length and thickness, which
slows its deterioration rate.
But the larger size is associated with
higher costs. “A Category 4 MD pump
might have an impeller with an OD
of 600 mm and an ID of 200 mm. A
Category 3 with an aspect ratio of 2.5
that can produce the same duty only
needs an impeller with a 500 mm OD for
the same inlet size. So a pump capable
of producing the same flow and head has
an impeller, a volute and a frame size that
are all physically smaller by some 25%,