Chemical Engineering September 2014 - 56

Feature Report
Part 1
Magnetically Driven
Pumps: An overview
Understanding sealless pump technologies
and their potential applications
Richard Tym
ITT Goulds Pumps
M
agnetically driven (mag
drive) centrifugal pumps
have been in use since
1947 when the first magdrive
pump was developed. Mag
drives have always been the workhorse
pump in applications with
corrosive and often toxic fluid applications,
and particularly over the
last 20 years they've become more
common in the chemical process industries
(CPI).
A typical mag-drive pump is comprised
of a magnetically coupled
rotor-and-drive assembly separated
by a containment shell that hermetically
seals pumpage from the atmosphere
(Figure 1). The mag-drive
pump's key feature is a sealless
design, which eliminates a mode of
failure. This often makes it a strong
solution for pumping applications
with mechanical seal problems.
The mag drive is commonly used to
pump hazardous and high intrinsic
value pumpage where the process
cannot or should not be diluted by
flush media (typical in a traditional
mechanical-seal pump). Mag drives
have many growing applications
in global industries, such as petrochemicals
in petroleum refineries,
pharmaceutical applications, and
pulp-and-paper mills, which employ
caustic, acid and solvent services
during production. However, this
type of pump is somewhat underutilized
in many of these industries
due to common misconceptions
about the technology.
Figure 1.
The main components
of a mag-drive pump
are shown in this
cross section
Source:
ITT Goulds
Pumps
Mag-drive fundamentals
Magnetically driven pumps have
several design features that extend
pump life, especially in common CPI
applications with hazardous scenarios.
The mag drive's key design feature
is the absence of a traditional
rotating mechanical seal (compare
Figure 1 and Figure 2). Instead, a
full hermetic seal with no rotating
component reduces the risk of leaks.
This sealless design is the most wellknown
feature of mag drives and is
a primary reason why they are often
used for hazardous or valuable fluids.
Another advantage is avoidance
of mechanical seal maintenance and
flush plan maintenance.
Mag-drive pumps are available
in either ANSI or ISO dimensional
standards. They are available in
most metallurgies, as well as nonmetallic
designs, such as with a
polymer lining. A polymer design offers
improved corrosion resistance,
utilizing polymer coatings such as
EFTE (ethylene tetrafluoroethylene).
All mag drives, whether metal
56 ChemiCal engineering www.Chemengonline.Com September 2014
or lined, have very limited solids
handling capability. The nature of
the mag-drive design has circuits
that facilitate process lubrication
of internal bearings, and these passageways
are typically very small.
If solids are introduced, the circuits
can easily get blocked, leading to
pump damage. The passage ways
are sometimes so small that it will
take only a minute amount of very
small solids to erode the components
of a mag-drive pump.
Design and usage
In addition to the sealless advantages,
there are some key considerations
when deciding whether
to use a mag-drive pump. Because
they utilize magnets to transfer
power and torque from the drive
assembly to the driven rotor assembly,
it's important to recognize
that there are temperature limitations
for magnet's materials. When
exposed to temperatures above
their threshold they can begin to
lose their magnetism. Over time,
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Chemical Engineering September 2014

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