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TL-112

 

Shaft/impeller assembly of Vanton

Sump-Gard® vertical centrifugal pump

showing thick sectioned PVDF shaft

sleeve, ceramic bearing and key-driven

PVDF impeller.

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

Pumping Problems

INDUSTRY:

ENTITY:

SOLUTION(S) PUMPED:

PUMP TYPE(S):

Chemical

Various

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

deemed essential:

 

• 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

bromine.

 

• 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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Copyright 2016 - Vanton Pumps (Europe) Ltd - All rights reserved

About Us

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

mail@vantonpump.com

(+44) 01260 277040

Vanton Pumps (Europe) Ltd.

Unit 4, Royle Park

Royle Street

Congleton CW12 1JJ

UNITED KINGDOM

www.vantonpump.com