Shaft/impeller assembly of Vanton
Sump-Gard® vertical centrifugal pump
showing thick sectioned PVDF shaft
sleeve, ceramic bearing and key-driven
One of the early all-plastic Vanton sump
pumps designed for outside tank mounting.
Vanton Sump-Gard® sump pump of
bearingless design, with all-wetted
parts made of solid PVDF material to
resist the bromine.
Close up of PVDF caps which seal the
metal threads of bolts to avoid contact
with the liquid being handled.
Fluoropolymers & Custom
Engineering Solve Bromine
SUMP-GARD Thermoplastic Vertical Pump
Reprinted from CHEMICAL EQUIPMENT
By Edward Margus, VP of Engineering, Vanton Pump & Equipment Corp.
In the past 30 years, plastic pumps have come a long way in proving
their economic and performance advantages to the CPI. An example of
just how far pump designers have come in utilizing the latest advances
in plastics can be seen in the development of a line of pumps which
successfully and economically handle bromine liquid.
Bromine, a dark reddish brown liquid with a specific gravity of 3.11
indiscriminately attacks most metals including all of the Hastelloys®,
sparing nickel only if it remains free of moisture. The bromine element,
used in pharmaceuticals, gasoline additives, bleaches, fire retardants,
photographic products and, more recently, in manufacturing carbonless
copy paper is, perhaps, as good a test as any in demonstrating the
versatility of industrial grade plastic pumps. Experienced process
engineers, relying on conventional wisdom in specifying costly pumps
made of nickel, encountered serious and often disastrous problems
when bromine actually attacked the nickel components of these pumps.
Although nickel pumps are theoretically resistant to bromine, they rarely
lasted more than two months before requiring repairs, and as they
aged, their service life between repairs dropped to several days.
The culprit was uninhibited nickel corrosion caused by bromine
becoming wet by virtue of its deliquescent properties, which in turn
caused it to absorb atmospheric water.
Repairing nickel pumps in itself was a challenge. Many components
were difficult to procure and often had a delivery time of weeks or even
months. Dismantling these pumps was a hazardous procedure due to
their great weight, and the existence of many voids within which
residual bromine could lodge only to be released as unsuspecting
personnel dismantled the pump.
Adding to the maintenance problems was the tendency of bolts to freeze
in their tapped holes or nuts, and the complexity of their designs.
Fumes developing from splashing bromine have a potential of causing
serious skin and lung injuries. Usually, the costly long-length nickel shaft
had to be replaced. The quality of the hard-to-find barstock from which
these shafts were machined has always been variable with respect to
straightness, finish and dimensional accuracy, thereby creating the
potential for destructive vibrations and premature shaft failures.
Nickel pumps were never fitted with shaft sealing arrangements that
could effectively prevent the escaping of fumes past the pump shafts.
Maintenance personnel in many plants took to improvising their own
non-interchangeable sealing arrangements with limited success.
When a bromine pump must be pulled from its tank for servicing, the
procedure is long and arduous. A pump destined for repair must be
slowly hoisted from the tank, taken in small steps, to permit the bromine
to drain from the pump.
Large plastic sheeting is used around the exposed pump sections to
reduce the amount of vapors escaping from the tank. This process
alone takes about one hour. When the pump has been fully hoisted
from the tank, it must then be supported over a shallow pool of water
during disassembly. Entrapped bromine escaping from the pump as it is
dismantled will fall into the water where it is rendered less harmful.
Obviously these heavy nickel behemoths were not the answer for
pumping bromine. Indeed, escalating applications necessitated the
development of a better pump. Some bromine-using firms, desperate
for a viable alternative, tried pumps made of FRP. The results were
disastrous to the extent that the pumps could not even be repaired after
only a couple of hours of service.
In response to urgent requests from companies located in the US,
Europe and the Mideast, Vanton accepted the challenge of developing
and producing a line of sump pumps especially designed for
transferring bromine. The resultant pumps were to be produced from
solid virgin-grade PVDF, which was found after extensive research to be
totally resistant to bromine. Other noteworthy physical properties of
PVDF are its very high density, a relatively superior tensile strength,
good machinability characteristics, and excellent weldability.
A PVDF characteristic, uncovered by Vanton engineers during the initial
research phase, indicated a marked tendency of PVDF to sag or "bow"
when fabricated or molded into long slender lengths typical of
components used in manufacturing vertical sump pumps. A specially
developed design technique, utilizing structural reinforcements,
effectively coped with this inherent deficiency.
With the foregoing considerations in mind, Vanton engineers set out to
develop a line of bromine pumps consisting of vertical sump pumps,
outside mounted vertical pumps, as well as horizontal centrifugal
pumps. For reasons of personnel and environmental safety
considerations, the vertical sump pumps are preferred.
After evaluating the pumping application, the following features were
• Modular column construction where 30" column sections are bolted
together, using solid PVDF bolts.
• Smooth outside surfaces and, more importantly, internal drainage
holes to allow bromine to drain off from even the most remote areas.
• Complete sealing of discharge pipe by providing O-rings around its
outside diameter where it passes through the pump mounting plate.
• Pump mounting plates that conform to ANSI flange configurations to
provide positive closure of the opening of the bromine tank.
• Heavy-duty components to cope with the 3.11 specific gravity of
• One-piece gasket to be used under mounting plate.
Since the basic Vanton pump design limited contact of the fluid being
handled to the selected thermoplastic material, this presented no
serious problem. All parts of the pump exposed to the bromine liquid
were specified in solid-molded, extruded or machined PVDF. This
included the casing, impeller, column, and other components such as
bolts, nuts and washers. The stainless steel pump shaft would, of
course, be encased in heavy-sectioned PVDF sleeving with all sleeving
and the impeller welded together, then spark-tested to insure complete
isolation of the shaft from the bromine.
Vanton engineers then turned their attention to prevention of escaping
fumes. A unique shaft-sealing arrangement was developed for
positively retaining the bromine vapors within a tank or sump. It
consisted of a specially developed solid PVDF stuffing box packed with
woven Teflon® tetrafluoroethylene plastic which was fitted to the shaft
where it emerged above the mounting plate. Naturally, cooling of the
stuffing box was required. Since the usual water cooling cannot be
tolerated in bromine pumping applications, highly compressed nitrogen
gas was recommended for its refrigerant effect. Even so, nitrogen still
cannot carry off heat as effectively as water. Thus generous amounts of
radiation surfaces are provided within the stuffing box to assure
adequate heat exchange. Controlled nitrogen leakage into the bromine
tank assures a build-up of pressure to approximately 5 PSIG, inhibiting
vaporization of the bromine.
The heavy weight of the bromine presented a mechanical problem; one
of the applications called for an extremely large vertical pump with a
shaft length of I2'. The pump was designed to deliver 20 GPM at 100'
TDH, operating at 1750 RPM. This means that the pump has to operate
against 135 PSI.
In this particular application, there would be 12,830 pounds of force over
the cover area and each bolt would have to withstand 1200 pounds.
There was no way to do this with PVDF bolts. Nor could the PVDF
clamping flange resist ultimate buckling. Metal components would have
to be used.
Another problem was protection of the cast iron bolts and steel
clamping plates from the bromine liquid. To overcome this, each cast
iron bolt was coated with 50 mils of ECTFE. This fluoropolymer, like
PVDF, resists an extremely broad range of corrosive and hazardous
materials, including bromine. It has high tensile strength, toughness and
is impact-resistant. It is excellent as a coating material and was
considered ideal for the application. But a problem arose as to what to
do about sealing the cast iron bolt Acme threads, which cannot be
coated. The designers created a series of specially-engineered PVDF
sealing nuts. Internal O-rings isolate the threads from the bromine once
it engages the ECTFE coated surfaces, thereby simultaneously sealing
and tightening the bolts into position. The steel clamping plates holding
the casing and casing cover were also coated with 50 mils of ECTFE.
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In the 1950, Vanton developed a revolutionary all-plastic pump for use in conjunction with the first heart-lung device. The design limited fluid contact to only two non-metallic parts: a plastic body block and a flexible liner. This was the birth of our Flex-I-Liner rotary pump. Its self-priming sealless design made it an industry standard for the handling of corrosive, abrasive and viscous fluids as well as those that must be transferred without contaminating the product. Vanton now offers the most comprehensive line of thermoplastic pumps in the industry.
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(+44) 01260 277040
Vanton Pumps (Europe) Ltd.
Unit 4, Royle Park
Congleton CW12 1JJ