Chemical Engineering September 2015 - 54

FIGURE 4. Seal-less
sliding-vane pumps
are designed to maximize
bearing life and
minimize metal-tometal
contact
damage. leaks of hazardous materials that
reach the outside environment can be subject
to fines and remediation costs from the
u.S. environmental Protection Agency (ePA;
Washington, D.C.; www.epa.gov), as well as
other local and state regulatory agencies.
Additionally, other countries have their own
sets of regulations, which can often be more
stringent than those in the u.S. Spilled hazardous
materials also pose safety risks for
site personnel and cleanup crews, which
raises liability issues.
Most seal-less pumps, on the other hand,
have built-in safeguards that enable the
containment of the liquid in the event of a
catastrophic pump failure. Depending on the
level of protection required for the application,
further precautions can be taken by
utilizing double-wall containment shells and
leak-detection technology that triggers automatic
shutdown of the pump.
FIGURE 5. Some seal-less
internal-gear pumps feature
only one fluid chamber, which
not only enhances product
containment, but also eliminates
product entrapment,
especially when transferring
high-viscosity liquids
Seal-less pump technologies
While sealed pumps can perform sufficiently
in the manufacture, transfer and handling of
dangerous chemicals and other hazardous
materials, the shortcomings
that are inherent
in their sealed
design can make
them insufficient for
some jobs. In these
cases, manufacturers
should seek out alternative
pumping technologies
that can help
eliminate some of the
major concerns associated
with achieving full
containment, including
seal-less sliding-vane,
internalgear
and eccentric-disc
pumps.
S l i d i n g - v a n e
pumps. Seal-less
sliding-vane pumps
(Figure 4) generally fea54
ture
a magnetic coupling consisting of samarium-cobalt
magnets and a specially designed
bearing-and-head configuration that
allows a small quantity of the pumpage to
circulate through the containment can and
onto the bearing surfaces. This positive flow
of fluid minimizes temperature rise during
operation, which helps maximize bearing life.
replaceable 316 stainless-steel end discs
allow easy rebuilding of the pumping chamber
to like-new condition without having to remove
the pump from the piping. Additionally,
the pumps' carbon-graphite sleeve bearings
help ensure no metal-to-metal contact during
operation. Operationally, seal-less sliding
vane pumps offer the same advantages as
their sealed counterparts: volumetric consistency,
self-priming and limited dry-run capability,
drain plugs that facilitate draining and
easy replacement of worn vanes.
Internal-gear pumps. recent advancements
in internal-gear-pump (Figure 5) design
and operation have allowed for the development
of models that feature only one
fluid chamber. This method of construction
removes the adapter plate that is a staple of
traditional two-chamber magnetically coupled
internal-gear pumps, which eliminates
product entrapment concerns, especially
when transferring high-viscosity liquids. Onechamber
operation is achieved through a
between-the-bearings design that places the
magnets directly on the pump rotor, resulting
in a simpler flow path and full leak-free product
containment. Some seal-less internalgear
pump models are also constructed of as
few as seven parts, which helps contribute to
an estimated 50% reduction in maintenance
costs when compared to sealed pumps.
There are also seal-less internal gear pump
models that are interchangeable with nearly
all competitive sealed or packed-gear pump
brands, enabling drop-in replacement.
Eccentric-disc pumps. Seal-less eccentricdisc
pumps (Figure 6) feature no mechanical
seals, packing, couplings, or even magnets
- the shaft is instead sealed by a double
stainless-steel bellows. Operationally, sealless
eccentric-disc pumps can still offer selfpriming,
dry-run and low-shear operation,
very high suction and discharge pressures,
the ability to pump both low- and high-viscosity
liquids and clean-in-place and sanitize-in-place
(CIP/SIP) capability. The pump's
eccentric-disc operating principle features
an eccentric shaft that rotates, allowing the
disc to form chambers within the cylinder.
When the discharge pressure exerts itself
against the eccentric disc, slip is prevented,
which gives eccentric disc pumps the ability
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Chemical Engineering September 2015

Table of Contents for the Digital Edition of Chemical Engineering September 2015
