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TL-108

 

Polypropylene sump pump is 20 ft. long

Shaft-and-impeller assembly is of

polyvinylidene fluoride except for

ceramic bearing

Centrifugal pump has parts of ethylene

chlorotrifluoroethylene

Vertical cantilever bearingless pump with

dry run capability

Automated dual pump/tank system for

collection and transfer of laboratory

wastes.

Mobile unit can store and pump corrosive

liquids at various locations within plant

Sump pump set in skid mounted double wall

tank to collect hazardous waste.

Polypropylene centrifugal pumps move

50/gal/min of sodium hexametaphosphate

When to Consider
Plastic Pumps

INDUSTRY:

ENTITY:

SOLUTION(S) PUMPED:

PUMP TYPE(S):

General

Various

Various

CHEM-GARD Horizontal Centrifugal Pump, FLEX-I-LINER

Sealless Self-Priming Peristaltic Pumps, Nonmetallic Tank

Pump Systems, SUMP-GARD Thermoplastic Vertical Pump

They come in a broad range of materials, each

offering its own attractions.

 

Reprinted from CHEMICAL ENGINEERING

Edward Margus - Vanton Pump & Equipment Corp.

 

A process engineer considering the use of a plastic pump faces two

basic questions: Is a plastic pump better than a metal one for my

situation? If so, what plastics and elastomers should I specify?

Plastic pumps have become the choice in more and more process

situations as their qualities and capabilities have risen. However, the

typical engineer remains far less familiar with plastic pumps than with

metal ones.

 

Pumps made of thermosetting resins are available. However, those

made of thermoplastics are of special interest in the process industries

because of their wide-ranging inertness, as discussed in the next

section.

 

Why consider plastics?

 

Originally, plastic pumps came on the scene to handle fluids, such as

blood or hydrofluoric acid, that could not tolerate metals. That inertness

is still a key attraction. The materials are not corroded by the process

fluids, and conversely they do not contaminate the fluid. The latter

advantage is important in many fields, such as pharmaceuticals, foods

and electronic components.

 

Apart from resisting particular fluids, a given thermoplastic is likely to be

inert to a broader range of them than is true for metals. This provides

versatility.

 

Plastic pumps cost little to maintain. Their inertness makes for a very

long operating life. Plastic parts do not gall. Nuts and bolts are easy to

remove, threaded plastic components can be unscrewed readily, and

components of a disassembled pump can be reused. Thus, spare-parts

inventories can be kept to a minimum.

 

Also contributing to low maintenance is plastics' resistance to the

atmosphere. Since they don't corrode, plastic pumps need not

necessarily be painted.

 

As regards purchase price, the picture is mixed. Highly engineered

thermoplastic pumps cost less than equivalent pumps of expensive

metals or alloys (e.g., titanium or nickel). They are about on a par with

pumps made of Type 304 or 316 stainless steel. But they are likely to be

more expensive than equivalent ones of brass, bronze, aluminum or

cast iron.

 

A look at the limitations

 

The most obvious limitation of thermoplastic pumps concerns the

operating temperatures they can accommodate. Although a few

thermoplastics, particularly the fluoropolymers, can retain their

properties at temperatures as high as 550°F, commercially available

thermoplastic pumps are generally not recommended for continuous

service above 275°F. At higher temperatures, loss of mechanical

properties and stress-cracking corrosion may hinder performance. In

practice, this is not a widely relevant disadvantage, because corrosive

fluids are generally handled at moderate temperatures.

 

Pumps that employ flexible liners incur an additional temperature

limitation on the liner material. For instance, although a fluoropolymer

casing or body block may be suitable for high temperatures as indicated

above, the upper limit of the elastomeric materials is usually about

275°F.

 

As regards capacity, the upper limit for thermoplastic centrifugal pumps

on the market today is about 1,000 gal/min, with heads to 240 ft. The

largest rotary pumps cannot exceed 40 gal/min. The largest

thermoplastic magnetic-drive chemical pumps are limited to

approximately 400 gal/min against a total dynamic head of 40 ft.

Impact resistance and strength of thermoplastic pumps may also pose a

problem. They must be protected against falling objects and similar

impact dangers, because of possible deformation if the operating

temperature is high. Furthermore, thermoplastic material tends to

elongate under sustained load (creep) as temperatures rise.

 

For these reasons, thermoplastic pumps must generally be armored, by

surrounding the plastic with a metal sheath. This is particularly true of

horizontal centrifugal pumps that are exposed in normal plant

operations. Accordingly, these plastics' light weight cannot be

considered an advantage in those pumps (except to the extent that the

lightness of the plastic components within the armor eases

maintenance).

 

Light weight is, however, an advantage with respect to vertical

centrifugal pumps, particularly the larger ones. The same is true of

portable hand-held pumps.

 

Spotlight on materials

 

The selection of materials for a thermoplastic pump is highly relevant for

at least two reasons. One is the very broad range of polymers available.

The other is that, unlike the situation with pumps made of metal, the

engineer does not consult corrosion tables to help make the choice — a

particular plastic either works for a given situation or it doesn't, and that

information is readily available.

 

In spite of the breadth of the field, most thermoplastics used for pumps

fall into four basic categories: vinyl, polypropylene, polyethylene and

fluoroplastic.

 

When one considers use of those polymer families, a key parameter is

the service temperature. Some of the temperatures cited here may

seem conservative. That is because plastic components in pumps must

retain not only their shape but also adequate mechanical strength.

Vinyl

The ones most commonly used in pumps are polyvinyl chloride (PVC)

and chlorinated polyvinyl chloride (CPVC). PVC has good chemical

resistance and is an excellent choice for service temperatures to 140°F.

CPVC withstands temperatures to 210°F.

 

These materials are widely used throughout the chemical process

industries because they offer relatively low cost, good physical

properties, and resistance to attack by acids, alkalies, salt solutions and

many other chemicals. They are not generally suitable for use with

ketones, esters, chlorinated hydrocarbons, or aromatics.

 

Polypropylene

 

These increasingly popular low-cost polymers offer a good

strength-to-weight ratio, because of their relatively high stiffness and

their specific gravity of only around 0.90. Maximum service temperature

is 185°F.

 

They resist a broad range of acids, bases and solvents. But they are

generally not recommended for strong oxidizing acids, or for

chlorinated hydrocarbons and aromatics.

 

Despite that limitation, polypropylene pumps (and other equipment) are

widely used in the petroleum industry because the polymer resists

sulfur-bearing compounds. They are also attractive for water handling

and for waste treatment, and for laboratory service.

 

Polyethylene

 

This high-molecular weight material is impermeable to water and

generally resistant to organic solvents, acids and alkalies. It is among

the lightest of the thermoplastics, and retains good physical properties

even at low temperature. Polyethylene is attacked by strong oxidizing

acids and chlorinated or aromatic solvents. Maximum recommended

service temperature is 200°F.

 

Fluoropolymer

 

The three major fluoroplastics widely used in pumps for structural parts

are: polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and

ethylene chlorotrifluoroethylene (ECTFE). Each offers particular

attractions.

 

PTFE is perhaps the most inert compound known, so it can be exposed

to a extremely broad range of fluids. Its maximum service temperature,

500°F, is significantly higher than that of the other two.

 

PVDF is stronger, stiffer and less subject to creep than PTFE. It retains

strength well throughout its service temperature range. Its maximum

recommended service temperature is 300°F. It is chemically resistant to

most acids, alkalies (except sodium hydroxide) and organic solvents,

and is equally suited for handling wet or dry chlorine, bromine and the

other halogens.

 

ECTFE has high tensile strength and impact resistance. It is inert to a

broad range of acids, including the oxidizing types. It also can handle

alkalies, organic solvents (and combinations of them), most other

corrosive liquids, and abrasive mixtures, even when used as a coating

over metals. Maximum service temperature is 300°F.

 

All three of these fluoropolymers are suitable for applications requiring

extreme purity and freedom from contamination. Examples include

electronics manufacture and the handling of ultrapure water.

 

Elastomeric components

 

Thermoplastic pumps require elastomeric materials as well. These are

primarily used where corrosion resistance and impact resistance must

be combined with flexibility, as in gaskets, O-rings and other flexible

parts.

 

Natural rubber

 

It offers good resistance to weak and strong acids and alkalies as well as

to oxygenated solvents. It stands up well against abrasion and has good

low-temperature characteristics. But it is attacked by oxidizing acids,

and tends to swell in vegetable, mineral and animal oils.

 

Butyl rubber

 

Formed by the polymerization of butylene and butadiene, this synthetic

elastomer has good resistance to corrosive chemicals in general,

including outstanding resistance to dilute mineral acids. It also resists

vegetable and mineral oils. It stands up very well under heat, and offers

low gas permeation. It is not recommended for use with petroleum

solvents or aromatic hydrocarbons.

 

Buna-N (nitrile rubber)

 

This copolymer of butadiene and acrylonitrile has good resistance to

weak and strong acids as well as alkalies, and is highly inert to aliphatic

hydrocarbons, petroleum, and mineral and vegetable oils. It has

excellent water-swell resistance, and its mechanical properties actually

improve at higher temperatures. Buna-N is not recommended for use

with highly polar solvents such as acetone, methyl ethyl ketone, and

chlorinated hydrocarbons.

 

Neoprene

 

It offers excellent resistance to dilute acids and weak and strong alkalies,

and good resistance to petroleum, oils and concentrated acids. It is not

recommended for strong oxidizing acids, esters, ketones or chlorinated

aromatic hydrocarbons.

 

Ethylene-propylene-diene monomer (EPDM) rubber

 

This synthetic elastomer affords excellent low- and high-temperature

characteristics. It resists attack by a wide range of acids and alkalies,

detergents, phosphates, ketones, alcohols and glycols. EPDM does not

tend to absorb fluid, or to swell. It is not recommended for use with

aromatic hydrocarbons.

 

Chlorosulfonated polyethylene

 

It offers good resistance to dilute and concentrated acids, and alkaline

solutions regardless of their pH. Resistance to strong oxidizing acids is

excellent.

 

Other elastomers

 

Copolymers of vinylidene fluoride and hexafluoropropylene have

excellent resistance to oils, fuels, lubricants and most mineral acids, and

stand up against many aliphatic and aromatic hydrocarbons that attack

other rubbers. They are not recommended for low molecular weight

esters or ethers, or for ketones or certain amines, or for hot anhydrous

hydrofluoric or chlorosulfonic acids. Copolymers of perfluoromethyl

vinyl ether and tetrafluoroethylene offer virtually unmatched resistance

to all classes of chemicals, except fluorinated solvents. Continued use at

temperatures to 550°F is possible, and intermittent use to 600°F. The

material neither creeps nor flows, and it becomes more elastic rather

than embrittled with heat aging. The major disadvantage is extremely

high cost.

 

In addition to the structural thermoplastics and the elastomers,

thermoplastic-pump manufacturers sometime employ ceramics in seal

components. Two of the most common are a ceramic-graphite

composite with a silicon carbide surface that stands up well against

abrasion and heat, and a sintered silicon carbide that offers extremely

high corrosion resistance to aggressive liquids and solutions, such as

bromine.

 

Assuring quality and reliability

 

The engineer should insist that the supplier test every pump before

shipment, rather than relying on random sampling. Testing should in all

cases include output flowrate, head pressure, and energy input.

Centrifugal pumps should also be hydrostatically checked for leaks up

to the rated seal pressure. Hydraulic Institute (Cleveland, Ohio)

guidelines should be followed for all testing.

 

Routine vibration testing can be carried out by sound and touch, but the

findings should be checked with a vibration meter if they appear to be

borderline. Shaft straightness and runout should be examined, and

runout of impellers and similar circular parts should be assessed by an

indicator on a motorized fixture.

 

Be sure to specify that the pump impellers be dynamically balanced.

Forestalling shaft vibrations not only makes for accurate flowrates and

long seal life but also can help the pump meet workplace-noise

limitations, such as those of the U.S. Occupational Safety and Health

Administration. Pump buyers' concerns about erosion stemming from

surface grinding or hole drilling required for balancing are unwarranted.

Edited by Nicholas P. Chopey

 

PLASTIC PUMPS' PROGRESS

 

Plastic pumps came into prominence because of their early use as a

mechanism for transferring human blood without contamination or

destruction of the cells. The original pump used as an artificial heart was

of the flexible-liner design, having a pure-gum-rubber liner and a

transparent polymethyl methacrylate housing.

 

Like the industrial versions that have since grown out of it, this rotary

heart pump operates by means of an eccentric shaft within the liner. A

rotating eccentric lobe pushing against the liner creates a progressive,

compressive force that propels the liquid between the wetted side of

the liner and the inert pump casing. Some 150,000 industrial plastic

pumps of the flexible-liner design are in service today in the U.S. alone.

They can handle gases or liquids, including viscous fluids up to 8,000

SSU.

 

These pumps are often mistakenly confused with two types of

progressive cavity pumps, each also available in plastic. One is the

progressive-cavity screw pump, employed mainly to handle highly

viscous materials such as toothpaste, glues, grease or sludge. The other

is a peristaltic pump of flexible tubing design, often used for corrosive

or flammable fluids. Gear pumps are available in plastic. And the use of

plastic diaphragm pumps has risen recently.

 

Horizontal centrifugal pumps employing plastics were already appearing

on the industrial scene 30 years ago. At first, pump manufacturers

merely re-created the design and configuration of the standard metal

pump, using plastic components where possible for fluid contact areas.

But as the market grew, pump designers started to take advantage of

the superior chemical inertness, abrasion resistance, low weight and

precision moldability of the newly emerging engineered plastics. This

led to nonmetallic pumps with many design components that were

radically different from their metal counterparts.

 

It was only natural that the vertical centrifugal or sump pump would not

be far behind. Stimulated by the tremendous growth in the municipal

and industrial water- and waste-treatment fields, engineers have been

designing sump pumps with unique characteristics. For example, as

waste-gathering sumps have become deeper, vertical centrifugal

pumps have been redesigned to be suitable for depths of 20 ft. and

more.

 

Magnetic pumps with plastic components have also been undergoing

much development. State-of-the-art versions make wide use of

fluoropolymers for housing linings, are of rugged construction, and

offer almost universal chemical resistance, in some cases to

temperatures of 300°F. The housing linings may be of thick-walled PTFE

or PVDF, and are supported by shells of ductile iron.

 

 

 

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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