TL-116

 

Cut-away of polypropylene centrifugal

pump with PVDF impeller to extend

service life in abrasive applications

A PVDF impeller, stainless steel shaft

sleeved in PVDF and ceramic sleeve

bearings

The Plastic Alternative

INDUSTRY:

ENTITY:

SOLUTION(S) PUMPED:

PUMP TYPE(S):

General

Various

Bromine, Hydrofluoric acid, Corrosive slurries, Hot brine

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

Sealless Self-Priming Peristaltic Pumps, Nonmetallic Tank

Pump Systems, SUMP-GARD Thermoplastic Vertical Pump

While chemical inertness is the major reason for

specifying a plastic pump, users can take advantage

of other benefits as well

 

Reprinted from PUMPS AND SYSTEMS

By Ken Comerford

 

A variety of nonmetallic materials are available to meet your needs.

Not so long ago system designers would consider the use of plastic

pumps only if available metal pumps were completely unsuitable. Plant

engineers had learned to live with costly downtime and excessive

maintenance due to corrosion. Extensive research activities

concentrated on published corrosion rates for a long list of metals and

exotic alloys in an endless array of chemical solutions at varying

temperatures. Specific metal selection for a given application was left to

the user's discretion, based on what were considered to be "allowable"

rates of attack.

 

Unlike metals, with their anticipated corrosion rates in mils penetration

per year, plastics are either inert to or not suitable for a given fluid.

Selection, therefore, tends to be less complicated. In a recent study of

plant engineers and consultants who indicated they were using or

specifying plastic pumps, the number one reason given for their

selection of a specific pump was superior corrosion resistance.

 

Although there are many other reasons for specifying plastic pumps,

chemical inertness is the major one. No other reason comes close. The

benefits that accrue because of this resistance explains why plastic

pumps are being used today in almost every facility handling corrosive,

hazardous, toxic, and other aggressive liquids, and slurries.

 

CURRENT DESIGN PARAMETERS

 

Today plastic pumps are being produced for flows in excess of 2,000

gpm, with heads to 280 ft, and for use at temperatures from below

freezing to 275° F. Recent developments have made it possible to

incorporate many design features directly related to the unique

properties of plastics into pumps that conform to ANSI specification

B71.3 for horizontal process pumps.

 

With the successful introduction of these pumps, it was only natural that

vertical centrifugal designs would follow. This is particularly significant

in light of the need for deep sumps in the wastewater field. The

advantage of lightweight, chemically inert plastics has stimulated a host

of creative engineering approaches, and these sump pumps are now

available in lengths up to 20 ft.

 

ADVANTAGES OF PLASTIC PUMPS

 

Although the main advantage of plastic pumps is corrosion control,

there are many other benefits in applications that do not exceed their

temperature and pressure limitations.

• extended service life

• superior abrasion resistance

• freedom from contamination

• low maintenance

• broader range of usefulness

• low weight saves money

• low cost

 

PLASTIC MATERIAL OPTIONS

 

Although the materials handbooks list hundreds of nonmetallic

formulations with varying properties, for pump users the choice for

most applications narrows down to eight rigid plastics and eight

elastomeric materials. Choosing a specific material for use in an

application begins with a review of data published in handbooks and

"corrosion" tables. However, experience with actual conditions is

important. For this reason, we strongly recommend that pump

specifiers consult with manufacturers before recommending

nonmetallic materials for a new application. There is literally no

substitute for experience when it comes to material selection.

 

Take the basic consideration that limits the use of plastic pumps —

operating temperature. Although handbooks and specification sheets

prepared by material suppliers may show suitability of some plastics at

temperatures to 500° F, plastic pump manufacturers will generally not

recommend their product for continuous duty at temperatures above

275-300°F. The dynamics of pump operation, which include turbulence,

start-stop, wet-dry, abrasive particulates, and similar situations, suggest

that textbook laboratory test data be tempered by actual experience.

 

RIGID PLASTICS

 

The rigid plastics most widely used for pump construction are broadly

divided into two groups — thermoplastics and thermosets.

 

Thermoplastics have linear molecular chains that flow over each other

and separate when heated, then solidify into predetermined shapes

upon cooling. Reheating permits reforming without significant change

in properties. Thermosets, when heated, form permanent crosslinks

between linear chains, creating a rigid structure that cannot flow again.

Some thermosets are molded from liquid components that react to

certain chemicals at room temperature to create tightly crosslinked

chain structures. In either case, once the reaction is complete the plastic

cannot be reformed or remelted.

 

Thermoplastic materials are the group most widely used for corrosion

and abrasion resistance. Because they are homogeneous in structure,

they offer greater resistance to a broad range of aggressive solutions.

They also provide greater purity and can be used with ultrapure water,

pharmaceuticals, and foods.

 

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PVDF sump pump for handling bromine has

cast iron bolts encapsulated in ECTFE,

and Acme threads protected by PVDF

sealing nuts, isolating the bolts from

the corrosive solution. Heavy sheeting

of PVDF protects the underside of the

CPVC cover plate, and the stainless

steel shaft is sleeved in thick

sectioned PVDF.

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