Figure 1. Cutaway of a Vanton sump pump
with all immersed components of solid
homogeneous PVDF thermoplastic that is
inert to the corrosive bromine.
Pump Material Selection
Bromine, Sodium thiosulphate
SUMP-GARD Thermoplastic Vertical Pump
Back to Articles
Reprinted from World Pumps
Guide to the selection of materials for pumping the
In this second of a series of articles on materials selection for pumping
corrosive, abrasive and hazardous chemicals, George Black considers
the problems presented by bromine. Dense, toxic and highly
aggressive, its handling demands specialized pumping solutions, as
illustrated by a look at some actual field installations.
Bromine is a very dark, reddish brown, extremely heavy (specific gravity
3.11), corrosive and hazardous fluid derived from seawater and natural
brines by oxidation of bromide salts with chlorine. It is used in the
manufacture of ethylene bromide, a component of anti-knock mixtures,
as well as for water treatment, as an intermediate for fumigants, a fire
extinguisher fluid, and as bromide salts in pharmaceuticals,
photography, catalysis, and precious metal extraction. Other
applications include poison gas and shrink proofing wool. Its fumes are
toxic and irritating and it indiscriminately destroys most metals
including the stainless steels and exotic alloys, as well as most plastics.
Best results have been secured with the fluoropolymers.
Case history applications
Nickel components failed
Experienced process engineers were surprised when the nickel pumps
they specified for handling bromine provided an average of only two
months service before they had to be repaired. According to the
corrosion charts they used as guides, nickel is resistant to bromine as
long as it remains free of moisture. The problem was uninhibited nickel
corrosion caused by the bromine becoming wet by virtue of its
deliquescent properties, which caused it to absorb atmospheric water.
The short life of nickel pumps might have been acceptable if not for two
problems. One was the long and unreliable delivery time for the nickel
components. The other was the hazards involved with dismantling the
pumps. Pump designs involved many voids and cavities in which
residual bromine might be trapped and released during dismantling.
This danger, in combination with exposure to escaping fumes,
demanded an alternative solution. Initial attempts to substitute FRP
pumps proved disastrous. Service life was reduced to hours. The
answer has been found with the standardization on specially designed
vertical sump pumps with all fluid contact components made of solid
virgin grade polyvinylidene fluoride (Kynar PVDF) (Figure 1). To
minimize the danger from escaping fumes, a unique shaft sealing
arrangement was developed. It consists of a solid PVDF stuffing box
packed with woven Teflon (PTFE) fitted to the shaft where it emerges
above the mounting plate. Since the use of water for cooling this
stuffing box was out of the question, the use of nitrogen gas was
required. The necessary cooling along with inhibiting vaporization of
the bromine was accomplished with controlled leakage of highly
compressed nitrogen gas into the bromine tank.
Solving the heavy weight bromine problem
The 3.11 specific gravity of bromine presents a major mechanical
problem when large sump pumps are required. An application involved
a vertical Kynar PVDF pump with a 12-foot stainless steel shaft
completely isolated from the bromine by a thick PVDF sheath.
Conditions of service included delivery of 20 gpm at 100 feet TDH,
operating at 1750 rpm. This translates into operating against 135 psi,
and more than 1200 pounds of force over the cover plate, the clamping
flanges and the bolts. PVDF was out of the question for these
components because tensile strength would not be sufficient to
withstand the pressure. Here's how this problem was solved.
The cover plate was supplied in high strength chlorinated polyvinyl
chloride (CPVC), but the underside, the surface in contact with the
bromine, was provided with a thick liner of PVDF. Steel bolts were used
to anchor the cover plate to the top flange of the pump, but they were
sealed off from the fluid by special caps made of PVDF (Figure 2).
The clamping plates were furnished in structural steel, and the bolts in
cast iron. Both the plates and the bolts were isolated from the fluid by a
50-mil coating of ethylene chlorotrifluoroethylene (Halar ECTFE). This
fluoropolymer, like PVDF, resists the corrosive bromine and is an
excellent coating material. The exposed threads of the
PVDF-encapsulated cast iron bolts could not be satisfactorily coated, so
they were isolated from the fluids with PVDF sealing nuts (Figure 3).
Long service life with peristaltic pump design
The facilities at a chemical company were designed for toll and contract
bromination of organic chemicals. This required a self-priming pump
that could safely transfer liquid bromine with minimal maintenance. A
leakproof pump design was essential to protect plant personnel from
fumes or direct contact with this corrosive fluid. In this application the
bromine was pumped from drums of the nickel/copper INCO alloy
(Monel) to a glass-lined steel reactor through a Kynar® (PVDF) piping
system with a glass elbow in the line to observe the flow. The drum is
scale-mounted to monitor flow rate and the amount of bromine added
to the reactor. Air entering the drum during the pumping action passes
through a drying column to remove moisture that could react with the
bromine and form destructive hydrobromic acid.
The decision was made to use a flexible liner, rotary pump design,
which transfers fluid by means of a gentle peristaltic action with minimal
turbulence. The pump selected has only two components in contact
with the fluid — a thick-sectioned Teflon® pump body and a readily
replaceable Viton Fluoroelastomer flexible liner (Figure 4). Pumping
action is by an eccentrically mounted rotor pressing against the inner
surface of the liner and progressively moving the fluid trapped in the
channel between the outer surface of the liner and the pump body. This
unique sealless pump design eliminates leakage, toxic emissions and
similar problems associated with shaft seals, check valves, gaskets or
stuffing boxes (Figure 5).
The pump was furnished with a rotary vane air motor to control the
speed and regulate the flow of the bromine. In this application the
motor is operated at 300 rpm providing a controlled pumping rate of
0.25 gpm or 5 lb/min of bromine. At the time of this report, the pump
had been in service for five years, operating an average of 4.5 hours per
day. At the end of each day's run, the pump is flushed with sodium
thiosulphate. The low cost flexible liners are changed quarterly since
over time changes in their resiliency affect the accuracy of the metering.
Average maintenance time for liner change is reported to be
approximately 30 minutes, and is done without the use of special tools.
Figure 2. Close-up of PVDF caps that
seal the metal threads of bolts joining
the CPVC cover plate, which is isolated
from the bromine by a protective layer
of PVDF material.
Figure 3. Steel clamping plates and cast
iron bolts are completely isolated from
the bromine by a 50 mil coating of
ECTFE. The threads are then protected
from the fluid by PVDF sealing nuts.
Figure 4. Installation of a seamless
flexible liner rotary pump with
speed-controlling air motor. This unit
has provided many years of trouble-free
service. Only two components are in
contact with the bromine: the
heavy-sectioned pump body of PTFE and
the Viton fluoroelastomer flexible liner.
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.
Stay in touch
(+44) 01260 277040
Vanton Pumps (Europe) Ltd.
Unit 4, Royle Park
Congleton CW12 1JJ