Cut-away of Vanton Chem-Gard®
polypropylene pump with PVDF impeller
and PVDF thick sectioned shaft sleeve.
These horizontal centrifugal pumps
helped solve the severe
corrosion/abrasion problem created by
the pumping of an etching solution of
hydrofluoric acid and a proprietary
powder compound. Both metal and FRP
pumps previously specified for this
service resulted in repeated failures
and costly maintenance.
How to Select a
Pollution control, Wastewater Industrial, Wastewater
CHEM-GARD Horizontal Centrifugal Pump, FLEX-I-LINER
Sealless Self-Priming Peristaltic Pumps, Nonmetallic Tank
Pump Systems, SUMP-GARD Thermoplastic Vertical Pump
Reprinted from POLLUTION ENGINEERING
By Edward Margus and Kenneth Comerford
Pumps constructed of various non-metallic materials
are widely used in wastewater and other pollution
The use of non-metallic pumps for applications involving water and
wastewater treatment, pollution control and other related services has
been expanding at a dramatic rate for a variety of reasons. Some of
these reasons are related to the growing awareness of the need to
protect our environment and natural resources. Others are mandated by
government regulations. Still others are associated with the
development of new and superior engineered plastics and the
corresponding economic need to extend equipment life and improve
The information presented here is based on the answers to a
questionnaire sent to consulting engineers, system designers, plant
operators and plant managers, querying them on pump types,
construction materials and applications in the environmental industry.
Non-metallic pumps for environmental use
Although pumps trace their origin to early civilization, plastic designs for
industrial and similar heavy-duty service are relative newcomers. The
first such pumps were developed in the post World War II period,
coincident with the advent of synthetic materials. Because of their
chemical inertness, the pumps were widely used in the chemical
process and manufacturing industries.
Where are non-metallic pumps used in the environmental industry? The
overwhelming majority, more than 97 percent of the respondents,
indicated non-metallic pumps are used in their facilities in water,
wastewater treatment and other environmental applications.
Respondents also were asked what pump types are used at their
facilities. Using partially aided recall, the questionnaire listed three basic
pump types — centrifugal, vertical (sump) and rotary. Several "other"
pump types also were identified by respondents (Table I).
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Non-metallic materials of construction
To simplify response to the question about which non-metallic materials
of construction were used for the wet-end components of pumps used
in wastewater and related service, the seven materials most commonly
used were listed. The participants in the study doubled the number of
materials listed (Table 2).
Selecting the most effective material for a given application is extremely
important. There is no substitute for experience in material selection.
Engineered plastics have greater tolerance for a broader range of
corrosives. Unlike metals, which have a corrosion rate for given
chemicals, engineered plastics are usually either totally resistant or
Detailed information on the usefulness of individual plastics is available
from the materials manufacturers. This information, normally resulting
from static immersion tests, should be consulted for new applications.
However, data available from pump manufacturers is very significant
since it represents a dynamic test, and the wet end of the pump is
where the material gets its most severe exposure.
When dealing with plastics, one of the major parameters is service
temperature. Manufacturers tend to be conservative when it comes to
the working temperatures for which they will recommend their pumps.
The plastic components must be able to retain their shape and maintain
the mechanical strength requirements at the temperature level.
Several materials are used in engineered pumps for water, wastewater
and related environmental applications. Some of the most common are:
POLYVINYL CHLORIDE (PVC). Perhaps the most common thermoplastic
material used in pump construction, PVC is a relatively low cost material
characterized by high physical properties and resistance to corrosion
and chemical attack from a broad range of acids, caustics and salt
solutions. PVC tends to be attacked, however, by solvents such as
ketones, chlorinated hydrocarbons and aromatics. PVC is generally
used at ambient temperatures and is not recommended for pump
service above 140°F.
CHLORINATED POLYVINYL CHLORIDE (CPVC). CPVC has physical
properties and chemical resistance similar to PVC. The major difference
is its higher useful temperature limit, which for pumps is 210°F, and its
correspondingly higher pressure ratings at these elevated temperatures.
CPVC is suitable for corrosive liquids at elevated temperatures as well
as for low temperature liquids.
POLYPROPYLENE (PP). Polypropylene is the lightest of the industrial
grade plastics, having a specific gravity or density of 0.90. This popular
polymer offers an excellent strength-to-weight ratio and is
recommended for pump service at temperatures to 185°F. In addition to
resisting acids and alkalies, polypropylene is also highly resistant to
organic solvents. Polypropylene is not recommended for use with
strong oxidizing acids, chlorinated hydrocarbons or aromatics.
POLYVINYLIDENE FLUORIDE (PVDF). PVDF is a strong, tough and
abrasion resistant fluorocarbon material. Because of its high density, it
resists distortion and retains its strength at elevated temperatures. PVDF
can be used over a wide range of temperatures, from -40°F to 300°F. In
terms of chemical resistance, PVDF is inert to most solvents, acids and
alkalies, as well as wet and dry chlorine, bromine and other halogens.
Its high hardness and low coefficient of friction make it ideal for
abrasion resistant applications. PVDF is recommended for use with
ultrapure water and reagent grade chemicals, as well as other
applications where freedom from contamination is important.
POLYETHYLENE (PE). This ultra high molecular weight (UHMW) material
is impermeable to water and resistant to organic solvents, acids and
alkalies. PE is very similar to polypropylene and retains good physical
properties at low temperatures and also up to 200°F. Its hard smooth
surface makes PE useful for abrasive solutions.
FIBERGLASS/GLASS REINFORCED POLYESTER (FRP/GRP). These
thermosetting materials are polyesters reinforced with glass or other
fibers to provide additional strength. They are closer to metals in their
structural properties than the thermoplastic materials, but are not as
chemically resistant. Since FRP/GRP is a composite material rather than
a homogeneous polymer, there is potential for forming capillary
passageways that result in wicking. This limits the application of these
materials, particularly if the same pump is to be used for different
chemicals. It also limits their use in abrasive service. Maximum service
temperatures for pumps made of these materials is 230°F.
ETHYLENE CHLOROTRIFLUORETHYLENE (ECTFE). This material resists
an extremely broad range of acids including oxidizing types, the
alkalies, and most other corrosive and abrasive fluids. ECTFE is very
similar to PVDF. It offers excellent barrier properties suitable for
ultrapure water and similar fluids where contamination could be a
problem. ECTFE has extremely high tensile strength as well as impact
resistance. It is recommended for temperatures to 300°F.
POLYTETRAFLUORETHYLENE (PTFE). This material is most commonly
referred to as Teflon. It is one of, if not the most inert of the
thermoplastics available. PTFE retains useful mechanical properties at
temperatures as high as 500°F. It offers excellent impact and abrasion
resistance. Compared with the other fluoropolymers, however, its
tensile strength and creep resistance are low.
The above covers the rigid materials generally used for pump
construction. Other materials mentioned by respondents refer to
elastomeric components, primarily gaskets, O-rings, flexible liners and
other parts that require corrosion and impact resistance combined with
Why plastic pumps are selected
Plastics represent a large family of synthetic materials with a number of
common characteristics. They share the same basic molecular
structure, and being manmade, they can be readily modified and
compounded to achieve a wide variety of physical properties and
behavior patterns. The term "polymers" frequently used in relation to
plastics refers to their molecular structure. They consist of very large
chain-like molecules, made from various organic substances called
monomers. The chemical reaction used to link and form the monomers
into polymers is polymerization.
Although thousands of plastic compounds exist, the reasons for
selecting specific ones for pump construction are summed up in Table
Corrosion resistance, not surprisingly, was listed as the primary reason
for selecting plastics for pump construction. We were somewhat
surprised, however, to see the relatively high position of "price" since
pumps made of engineered plastic are similar in cost to pumps made of
type 316 stainless steel.
Engineered plastic pumps, built to the standards required for resisting
corrosives or for use in rugged service offer advantages over metal
pumps in terms of longer service life and lower maintenance, but not
necessarily in terms of original price. They are, however, less expensive
than pumps of exotic materials such as Alloy 20, Hastelloy, Nickel or
Other reasons for using plastic pumps mentioned by respondents were
purity, environmental protection, flexibility and non-sparking in an
explosion-proof environment. Another reason for specifying engineered
plastics is low maintenance. Plastic parts do not gall or seize the way
metal parts do. Nuts and bolts and other hardware are easy to remove
and threaded plastic components can be unscrewed readily and reused.
Plastic pumps are easy to keep clean and do not need to be painted
since they don't rust.
Non-metallic pump applications
Approximately 100 specific applications for nonmetallic pumps in
wastewater and pollution control service were listed by the respondents
(Table 4). These applications fall into several basic groups:
• Transfer chemicals from bulk storage to day tanks.
• Metering chemicals and polymers.
• Chemical feed to scrubbers and condensate pumping.
• Odor control systems.
• Groundwater remediation and landfill leachate treatment.
• Lift station collection and wastewater treatment.
Bad experiences with non-metallic pumps
The majority of respondents said they had not had a bad experience
with non-metallic pumps. Of those who had, most offered their own
carelessness, negligence or lack of knowledge as the primary cause.
The bad experiences of respondents fell into four basic categories:
• Buying low quality because of low price.
• Improper applications, selecting the wrong materials, the wrong pump
or improper design.
• Poor installation, often due to carelessness
• Improper maintenance, often due to unfamiliarity with recommended
maintenance procedures for plastic pumps.
The most common material-related selection problem appears to be
improper use of thermosetting FRP/GRP pumps in severe
corrosive/abrasive applications. Switching from thermoset to
thermoplastic pumps helped solve the problem in many cases. In some
abrasive applications where polypropylene pumps were originally
selected, impeller wear was overcome by switching from polypropylene
impellers to PVDF.
A number of respondents referred to difficulties under cold or freezing
temperatures, particularly when PVC was the basic material. One
solution is to specify PVDF instead of PVC because it maintains its
strength at temperatures as low as -40°F. Other solutions involve heat
tracing, proper insulation and special handling techniques.
Operating problems due to seal and bearing failure are the result of poor
maintenance practices. Analysis of the bad experience mentioned in the
responses points out the importance of working closely with the pump
manufacturers before specifying materials or design for difficult
The final question asked for information on pumping applications that
still cause the biggest headaches. The answers fit into two basic
groups: difficult-to-pump products and demanding operating conditions
(Table 5). Responses cut across all pump materials — metals and
The biggest headaches are associated with pumping sludges, heavy
slurries and high head, low flow conditions — things that have nothing to
do with the basic material selection and can cause problems for metal
as well as plastic pumps. With the exception of thick sludges and
sand/oil slurries, all of the difficult products listed by respondents can
be pumped with properly engineered non-metallic pumps. None of the
difficult operating conditions are beyond the scope of non-metallic
It also is obvious from the responses that satisfactory service life is a
relative term. Downtime is expensive. Extending it by days or even
hours is frequently of significant value. The larger the operation the
greater the significance in most cases. But in the environmental
industry, where equipment often operates in remote locations,
continuous operation is unrelated to the size of the operation.
This again highlights the importance of discussing pump problems with
the manufacturer and seeking out manufacturers who will modify
existing designs when off-the-shelf products can lead to expensive
Engineered plastic pumps have made strong inroads in water and
wastewater treatment, pollution control and related environmental
services. For maximum performance and efficient service life, the
emphasis should be on quality products engineered for the specific
corrosive or abrasive applications.
In addition to selecting the right materials of construction, the right
pump type and the necessary design features, it is imperative that care
be taken during installation and that sound maintenance programs be
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