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
The Plastic Alternative
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.
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
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