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2002 March edition
With
their elimination of leaks, with robust, all-metal construction,
sealless metal magnet-drive pumps (MDPs) are ideal for many applications
in the chemical and petrochemical industries where the handling
of hazardous fluids or high temperatures and pressures are the
order of the day. In this Japanese contribution,
Shigeo Takinomi of Sanwa Hydrotech Corp discusses the characteristics
and applications of sealless, metallic MDPs, and compares them
with other magnet-drive pumps and conventional sealed pumps. Sanwa
Hydrotech has been manufacturing sealless metal MDPs for some
two decades.
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The
world is currently facing important global issues, including ecological
destruction and depletion of natural resources.
Every industry is being challenged to help prevent global warming
and to detoxify, compress and recycle waste materials. Responsible
businesses are incorporating ecological considerations into their
management strategies, and many new ecology-minded products are
being developed to improve the planet. Sealless pumps - sealless
metallic magnet-drive pumps (MDPs) in particular - have been developed
primarily in response to the demands of the petrochemical and chemical
process industries. The role of sealless pumps has become more and
more important in this age of ecological awareness and industrial
sophistication.
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Figure
1.
The 25-MHP-HT from Sanwa Hydrotech is a sealless matallic
MDP designed to cope with high pressures up to 29.4 MPa and
high temperatures up to 450C. It has a maximim power of 0.75
kW,a head of 10 m and capacity of 20-30 l/min. |
Sealless
metallic MDPs
The primary purpose of sealless MDPs is to eliminate leaks. Sealless
metallic MDPs are designed to convey the driving power to the pump
casing through magnetic media by means of permanent magnets. No
shaft sealing is required in the pump; hence, there is no leakage.
This important characteristic provides safety, as well as reliability
of these pumps. Secondly, sealless metallic MDPs can be used in
high temperature and high pressure conditions, which were previously
considered too difficult for magnet-drive pumps and were only served
by conventional sealed pumps or other types of sealless pumps. Third,
with long mean time before failure(MTBF), compact design and the
latest construction materials, sealless metallic MDPs are user-friendlly
at all levels, to system designers, purchasers, operators, and to
our planet!
Use in existing industries
Huge numbers of process pumps are used in the chemical and petrochemical
industries. In these industrial sectors, pump manufacturers, plant
designers, plant managers and plant operators are challenged by
the varied characteristics of the fluids being processed and/or
the end products. Extreme measures are often required to cope with
these chemical/physical properties and the wide range of pumping
need. The fluid used in these industries vary widely and include:
acid, alkaline, ammonia, hydrocarbons, PCBs, coolants, thermo-fluids,
hot water, liquid N2, latex, molten sulphur, and many, many more.
Additionally, the varied characteristics of these fluids can range
from corrosive, abrasive, flammable, toxic, hazardous, low temperature,
high temperature, or high pressure. No one single pump can handle
all these liquids.
Prior to the dvelopment of sealless pumps, sealed pumps were primarily
used in these sectors. Huge effort was made to come up with appropriate
sealing solutions in conjunction with designs, function and peripheral
supporting parts, so that there is an enormous selection of mechanically
sealed pump models now available. Despite all these efforts, there
is no perfect shaft sealing available. Thus, one can easily conclude
that further challenging developments will be required in the future
for new technological demands.
The maximum performance limits that special
mechanical seals are capable of handling are 450 degC (842 degF)
and 20 MPa
(2000 psi). Sealless pumps, compared to conventional sealed pumps,
can be easily implemented into these difficult jobs. Sealless metallic
MDPs, in particular, are superior in their durability, their temperature,
pressure and corrosion resistance due to the metal structure, as
well as offering separate containment and zero leakage (Figure 1).
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| Figure 2.Comparison
of the construction of metal(left) and plastic(lower right)
magnet-drive pumps and canned motor pumps(upper right). |
By contrast, synthetic plastic MDPs and lined
MDPs have intrinsic limitations in temperature resistance of 100C,
and pressure resistance of 2 MPa. Canned motor pumps require protection
against high temperature, and extreme care is required to contain
the electric current, which is in close proximity to the pump casing(Figure
2).
Conventional sealed pumps are used widely for
water applications in mining, power stations, ship building and
general industry. In these less-sophisticated applications, no doubt
sealed pumps will continue to be used in the years to come. However,
even for water applications, sealless pumps are often specified
due to their outstanding reliability. As an example, in the early
1990s, sealless pumps were manufactured and built-in for cooling
circuits of thousands of super-computers (Figure 3).
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| Figure 3.The
MMA-FA magnet-drive pump developed use in supercomputers. |
The reliability and the compactness of sealless
pumps were the main reasons for this ground-breaking decision. For
pumping ultra-pure water in the computer industry, sealless pumps
play an indispensable role in preventing chemical reaction or contamination
of the process water circulating inside sensitive processing equipment.
The compact size of sealless metallic Sanwa MDPs with regenerative
turbine vane impeller designs makes these pumps especially useful
for cooling circulation for equipment processing semi-conductors
and LCD devices.
Other applications include use in the biotech, pharmaceutical, magnetic-transporting
and nuclear technology fields.
Configuration and materials of sealless metallic MDPs
In the fast-growing stage of sealless metallic
MDP development in the 1980s, primarily 'long-coupled' type pumps(outer
magnet and motor are connected through outer-shaft and motor coupling
with bearing supports) were available. 'Close-coupled' types (outer
magnet, outer coupling and motor drive shaft are connected directly)
were developed in the early 1990s. Because of the compact design,
economical efficiencies, easy installation, no shaft alignment,
energy efficiencies and proven safety and performance, close-coupled
sealless metallic MDPs are now preferred by many users over long-coupled
types. Long-coupled pumps do still play an important role in heavy-duty,
higher horsepower applications. They are typically used when numerous
optional peripherals, such as centre-line supports, steam jackets
and inducers, are required.
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| Figure 4.Magnetic
force as a function of temperature for magnet-drive pumps
using a) Nd and b) SmCo rare earth magnets. |
Sealless metallic MDPs can use rare earth neodymium
(Nd) or samarium cobalt (SmCo) magnets, depending on pumping temperatures.
Nd magnets are used at 150 degC (300 degF) and below. SmCo magnets
are used up to 450 degC (840 degF).
At high temperatures, magnet force is diminished (see Figure 4).
However, Sanwa Hydrotech's proprietary magnet coupling design can
help to prevent de-coupling of the magnet assembly, that is, the
device to convey drive power to rotate the shaft and impeller only
through magnetic force, comprised of the inner magnet coupling,
rear casing and outer magnet coupling.
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| Figure 5.
Designs for vertical applications include Sanwa Hydrotech's
'MPCP' for in-line applications. |
Figure 6.The
'MVIC' submersible pump from Sanwa. |
As with conventional sealed pumps, sealless
metallic MDP products are also available in designs for vertical
installations. Vertical sealless metallic MDPs range from in-line
applications to submerged installations (Figures 5 and 6). For in-line
applications, the relatively small installations area requirement
and identically-sized suction/discharge piping, make installation
easy. On submerged application, where leaks are not allowed, sealless
metallic MDPs are excellent for pumping hazardous or expensive fluids
from pits or storage tanks.
It is appropriate here to give a caution against
'dry run'. Running a pump without fluid is detrimental to any pump,
especially to MDPs. Internal bearings(bushings, shaft sleeves and
thrust rings, mounted inside the inner magnet coupling) made of
silicon carbide(SiC) will experience structural damage when subjected
to a sudden, severe temperature rise or drop caused by
'dry run'. In vertical pumps, as described above, the magnet couplings
are also mounted in a vertical position. In this position, air can
be trapped inside the rear casing and could cause dry run. However,
the magnet coupling design of sanwa vertical sealless metallic MDPs
takes this into account, with a pressure gap between the pump circulation
inlet and outlet bores which expels the trapped air in seconds upon
initial rotation, before the SiC parts have a chance to heat up.
New industrial
applications
Revolutionary industrial development has been
taking place in such sectors as semiconductor, pharmaceutical, medical,
food, ecology, nuclear and military technology. As Sanwa Hydrotech
we are confident that, not only for current industrial requirements,
but also for these new, unfolding industrial developments, sealless
metallic MDPs will be in demand due to their outstanding reliability,
long life, economical advantages, and their suitability and performance
in a wide range of applications. Critically-staged fluids (such
as water under critical temperature or pressure) are often required
for certain chemical reactions. Here, again, the reliability of
sealless metallic MDPs is called in for pumping these critical fluids.
A new sealless pump with shaft-less impeller
support is currently under development at Sanwa Hydrotech and in
expected to be on the market in this decade. Although cost is still
an issue, this pump will dramatically improve fluid contamination
caused by friction or abrasion on the surface of rotating parts.
In this radical new design contamination can only come from the
impeller, since there will be no shaft or bearings; the impeller
is designed to be supported and rotated inside the pump casing by
magnetic force alone. We believe this innovative design will find
new potential markets and further displace conventional sealed pumps
in existing industries.
Applying sealless metallic MDPs
In most cases, sealless
metallic MDPs are selected for the following pumping requirements:
1.Handling toxic or hazardous liquids where leakage cannot be tolerated.
2.High temperature or high pressure applications.
3.When long MTBF is required,and when low total cost operation is
advantageous.
Sealless metallic MDPs offer low total cost of operation when the
following points are considered:
1.Utility costs
2.Maintenance costs (labour and materials)
3.Parts replacement
4.Lubrication
5.Cooling requirements
6.Downtime for repairs.
At Sanwa, we believe the maintenance costs for sealless metallic
MDPs are about 30% of those for sealed pumps, over the lifetime
of the installation.
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TABLE
1.Cost COMPARISON CHART
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pump
type
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Initial
cost($)
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Overall
efficiency
(%)
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Power
cost
(US$)
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Maintenance
cost
(US$)
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EPA
monitoring
(US$)
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10-year
Lifecycle
cost
(US$)
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API 610
ANSI sealed
DIN canned
API vertical canned
DIN magnet drive
API magnet drive
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4600
2000
4200
5400
2900
3500
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64
71
53
64
47
47
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8000
7200
9700
8000
10900
10900
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20800
18200
4200
5400
2900
3500
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25100
25100
N/A
N/A
N/A
N/A
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58500
52500
18100
18800
16700
17900
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(Source World Pump
1992 edition)
Contact Japan
Shigeo Takinomi,
General Manager,
Engineering Department
Sanwa Hydrotech Corporation
11-33 Minami-kaneden 2 chome
Suita,Osaka 564-0044,
Japan.
obd@sanwapump.co.jp
Tel:+81-6-6330-5984
Fax:+81-6-6330-5975
Contact USA
Wallace Scott,
General Manager,
Magnatex Pumps, Inc
Tel:+1-713-972-8666
Fax:+1-713-972-8665
E-mail:sales@magnatexpumps.com
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