3. INTRODUCTION
Pumps used in high-purity applications such as
pharmaceutical processing and biotechnology
typically require a level of design that is higher than
in most other processing industries. The pumps
not only need to transfer product efficiently, but
they must also meet strict design and cleanability
requirements mandated by the many organizations
that establish standards for ultra clean processing.
Sizing and selecting a pump for any application
can be a tough task, but in the world of ultra-
clean processing, the stakes are higher, and the
requirements are more demanding so the challenge
can be a bit overwhelming. Your first priority should
be to partner with a qualified pump expert that
has the experience and the tools to do it right the
first time. Choose a pump partner with many years
of experience designing and building process
systems and who also understands pump design,
performance, and applications. Their expertise
will help you select the pump you need to get the
results you want.
This guide is intended for engineers, production
managers, or anyone concerned with proper pump
selection for pharmaceutical, biotechnology, and
other ultra-clean applications. In the following pages,
we look at the important considerations for choosing
the right pump for your high-purity application.
PUMP TYPES
The first big question in pump selection is: ‘What
type of pump do you need?’ To answer that, it
helps to understand a little about pump design and
consider the various pump styles that are available
to fit your application.
In general, there are two main categories of pumps
– kinetic and positive displacement. Each of these
categories is distinguished by the mechanics of
how they transfer fluids. Pumps in both categories
have advantages and disadvantages depending on
your high-purity requirements, and there are pumps
available in both categories with the necessary
hygienic features suitable for high-purity processing.
KINETIC PUMPS
Pumps of this type (also known as “dynamic” or
“rotodynamic”) are designed to impart kinetic energy
into the fluid to transfer it. They are characterized
by the use of an impeller that spins at high speed
to accelerate the fluid inside the pump casing.
The energy imparted into the fluid by the impeller
generates centrifugal force that creates pressure
as the fluid pushes against the outer area of the
casing. This pressure is the force that discharges
the product out of the pump’s discharge port and
through the process lines.
Centrifugal and self-priming pumps are two common
types of kinetic pumps in high-purity processing.
4. DISADVANTAGES
• Not recommended for viscous liquids.
• Not recommended for fluids with large
suspended solids.
• Not recommended for shear-sensitive fluids.
• Limited inlet suction (or “lift”). The inlet
must be adequately flooded to meet the
pump’s net positive suction head (NPSH)
requirements to avoid cavitation.
• Turbulence in the casing can cause surface
corrosion (rouging) on the casing’s internal
surface with some fluids.
• Flow rate is impacted by changes in head
pressure.
• Dynamic action of the impeller tends to
entrain air into product.
ADVANTAGES
• Excellent for transfer of low-viscosity fluids.
• Available with hygienic design and
traceability options for high-purity
applications.
• Flow rate can be easily adjusted with a
valve at the pump outlet.
• Low purchase cost compared with many
other pumps.
• Simple, reliable design is easy and
inexpensive to maintain.
• Small dimensional footprint.
• Steady, pulsation-free output.
• Available in single-stage through multi-
stage designs capable of a wide range of
flow and pressure outputs.
• Compatible with fluids containing some
suspended particulates or small solids.
ADVANTAGES & DISADVANTAGES
OF CENTRIFUGAL PUMPS
CENTRIFUGAL PUMPS
This style is by far the most common example of the
kinetic pump design. In fact, the majority of all pumps
currently being used in the processing industries are
centrifugal. Their dependability, hygienic design,
and relatively low cost make them a popular choice
for many high-purity applications.
Centrifugal pumps are typically the go-to choice
for transferring lower viscosity fluids. Since less
viscous liquids are much easier to accelerate with
kinetic energy, centrifugal pumps can transfer them
much more efficiently than other designs. They are
capable of very high flow rates with consistent,
non-pulsing flow and are available in multi-stage
versions for applications that require extremely high
output pressures.
Not all products are a good fit for the centrifugal
pump design. The high-speed impeller creates a
very dynamic environment inside the pump casing,
which may be harmful to some shear-sensitive
fluids. And while some centrifugal pumps are
capable of pumping fluids with viscosities as high as
1000 cPs, the efficiency of a centrifugal pump drops
considerably once the fluid viscosity exceeds about
100 cPs.
KINETIC PUMPS
PUMP BUYING GUIDE
4
5. DISADVANTAGES
• Not recommended for high viscosity fluids.
• Low capacity output compared to other
standard centrifugal pumps.
• Additional piping considerations may be
necessary.
ADVANTAGES
• Highly effective as a CIP return pump.
• Excellent for pumping fluids containing air
or gases.
• Capable of superior suction lift.
• Self-priming once the casing is half-filled.
• Minimal maintenance required.
SELF-PRIMING PUMPS
A self-priming kinetic pump usually plays a very
specific role in processing applications. It is specially
designed to pump fluids with entrained air or gases
without losing its prime – something that a standard
centrifugal pump has difficulty doing. This design
feature makes the self-priming pump an excellent
choice as a clean-in-place (CIP) return pump in high-
purity processing applications.
Self-priming pumps made by most top-quality
manufacturers are 3-A compliant with hygienic
options such as casing drains and better surface
finishes for internal surfaces. They may not be
sufficiently hygienic for product contact in high-
purity applications.
ADVANTAGES & DISADVANTAGES
OF SELF-PRIMING PUMPS
POSITIVE DISPLACEMENT PUMPS
Members of this pump category transfer fluid by
capturing and moving specific volumes of fluid from
the pump inlet to the pump outlet through the use
of rotational mechanical force. Unlike kinetic pumps
that accelerate fluid to generate flow and pressure,
PD pumps transfer product by physically forcing
fluid through the pump outlet.
Several different designs of PD pumps are suitable
for high-purity applications. Diaphragm or piston
pumps use a reciprocating motion to transfer fluids
and others; lobe or peristaltic pumps use a rotary
motion to do the job. Regardless of the design,
positive displacement pumps all share some
common characteristics. They all are very effective
at pumping high viscosity fluids, some as high as 1
million cPs. They are also known for their energy
efficiency, gentle product handling, and the ability to
maintain consistent flow rates in spite of fluctuating
head pressures.
6. ROTARY LOBE PUMPS
Rotary lobe pumps have two parallel shafts that
drive lobed rotors. As the shafts rotate in opposite
directions, the lobes on the rotors alternately mesh
and un-mesh with each other, repeatedly creating
then collapsing cavities to capture the fluid. Near
the pump inlet the lobes un-mesh, creating a low-
pressure cavity that helps to pull fluid into the
pump casing. The fluid becomes trapped between
lobes and is carried around the pump casing to the
discharge port. As the lobes mesh back together
near the outlet, the fluid cavity is compressed,
creating high pressure and forcing the fluid through
the outlet.
A common choice for pharmaceutical and biotech
applications, rotary lobe pumps are readily available
with hygienic options that make them a good fit for
high-purity processing. Although predominantly
used for transferring high viscosity fluids, rotary lobe
pumps are also very effective for transferring less
viscous fluids in low-pressure applications. Because
of their design, rotary lobe pumps are generally
unaffected by system pressures, so they generate a
constant flow regardless of changes in the process
head pressure. And since they discharge a specific
amount of fluid per revolution, their output is easily
controlled by varying the pump speed, typically with
a variable frequency drive (VFD).
DISADVANTAGES
• Low viscosity fluids can “slip” at high
output pressures, reducing efficiency.
• Typically driven with motor/gear reducer
unit creating large footprint.
• Requires use of pressure relief or safety
bypass valves.
• Moderate flow and pressure pulsation.
• Requires maintenance of two
mechanical seals.
• Some rotor styles may contact the
casing causing particulate shedding.
• Initial cost is typically higher than
centrifugals.
ADVANTAGES
• Ideal for high viscosity fluids.
• Offers accurate and consistent output.
• Gently handles shear sensitive fluids and
fluids containing soft or fragile solids.
• Available with hygienic design and
traceability options for high-purity
applications.
• Flow output is unaffected by changes
in head pressure, assuming sufficient
viscosity.
• Reversible direction of flow.
• Output can be controlled by varying
drive speed.
• Good suction lift capacity.
ADVANTAGES & DISADVANTAGES
OF ROTARY LOBE PUMPS
POSITIVE DISPLACEMENT PUMPS
PUMP BUYING GUIDE
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7. DIAPHRAGM PUMPS
Air operated diaphragm (AOD) or double-diaphragm
(AODD)pumps(sometimesreferredtoas“membrane”
pumps) are powered by compressed air rather than
electric motors or drives. They repeatedly compress
and decompress flexible diaphragms to pull fluid
into the pump chamber then push it out. Check
valves control the flow of fluid in and out of the pump
chambers during each stroke. Diaphragms separate
the pump drive components from the wetted area,
so they don’t have a mechanical seal, which makes
maintenance more straightforward and provides
superior cleanability. It can also run dry for extended
periods without damaging the pump.
Diaphragm pumps are excellent for metering
applications where highly accurate volume control
is critical. For this reason, they are commonly used
in high-purity processing for dosing, coating and
filling operations, chromatography, fluid injection,
and aseptic transfer of proteins, cells and other
materials.
One characteristic common to diaphragm pumps
is significant pulsation. While pulsation-dampening
devices are available for reducing or eliminating
unwanted pulsation, consider them carefully to be
sure they meet the cleanability requirements of your
high-purity application.
Air-operated diaphragm pumps, also known as
“multiple-use” pumps, can be cleaned-in-place (CIP)
or steamed-in-place (SIP) and reused many times.
Single-use versions have pump chambers designed
for just one process or batch. With single-use pumps,
the pump chamber is removed and discarded after
each process and replaced with a new chamber.
Chamber replacement can save time and money by
avoiding some cleaning and validation procedures,
and it eliminates the risk of cross-contamination
between batches or products. If products are
changed frequently and require quick changeovers,
single-use AODDs may be a wise choice.
DISADVANTAGES
• Significant flow and pressure pulsation.
• Not recommended for high-pressure
applications. Fluid output pressure is
limited to the air pressure available to
drive the pump, typically around 120 psi
maximum.
• Low maximum flow capabilities compared
to other pumps.
• Vibration and air venting can create a
significant amount of noise.
ADVANTAGES
• Excellent for high viscosity fluids, large
suspended solids or high suspended
solids content.
• Well suited for hazardous environments
due to the air-powered, intrinsically safe
design.
• Common choice for areas where electricity
is unavailable or not allowed.
• Available in a wide variety of metal and
non-metal materials.
• Pump can run dry for extended periods
without damaging the pump.
ADVANTAGES & DISADVANTAGES
OF DIAPHRAGM PUMPS
8. TWIN SCREW PUMPS
Twin screw pumps conforming to 3-A Sanitary
Standards can serve in CIP return applications.
Their unique design allows for the same pump
to perform both process and CIP. Twin screw
pumps can typically move soft solids delicately,
without damaging the product or compromising
visual integrity.
Twin screw pumps are typically self-priming and
have a low net positive suction head (NPSHr) for tank
emptying. Twin screw pumps can handle up to 60%
of entrained air, reducing cavitation and allowing for
constant gentle product flow even at high speeds.
Twin screw pumps are capable of handling shear-
sensitive products due to their tight manufacturing
tolerances and screw shape.
The twin screw pump housing and two contact-free
screws form closed chambers that constantly move
towards the discharge end of the pump. Pumped
fluid flows through screws in an axial direction. Twin
screw pumps can operate over a wide speed range
to function in hygienic applications for pumping
product at low speed and CIP fluid at high speed.
DISADVANTAGES
• Higher initial cost of ownership
• Performance is sensitive to changes in
viscosity
• Power requirement may be significantly
higher
• Additional maintenance requirements
ADVANTAGES
• Wide range of flows and pressures
• Delicate handling of most solids
• Wide range of liquids and viscosities
• High tolerance for entrained air
ADVANTAGES & DISADVANTAGES
OF TWIN SCREW PUMPS
POSITIVE DISPLACEMENT PUMPS
PUMP BUYING GUIDE
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9. PERISTALTIC PUMPS
In a peristaltic pump (sometimes referred to as a
roller pump, hose pump or tube pump), the fluid is
contained inside a flexible tube or hose that is curled
around the inside circumference of a circular casing.
The ends of the tube are connected to the inlet and
outlet of the pump. A single rotor with two or more
lobes is mounted in the center of the casing and
rotates within the casing. Rollers mounted on the
tips of the lobes compress the tube at pinch points,
capturing a very accurately controlled volume of
fluid in the tube between the pinch points. As the
rotor turns, the rollers alternately squeeze the tube
to force the fluid out then release the tube to allow it
to expand, drawing in fluid through the inlet.
Peristaltic pumps are a good choice for transferring
sterile fluids in low-flow, low-pressure applications.
They easily transfer viscous liquids and thick slurries,
and they are well-known for gentle handling of
shear-sensitive fluids such as cell suspensions. They
are extremely accurate and can be run continuously
or indexed with partial rotations to deliver smaller
volumes of product.
Their design is well-suited to the ultra-clean
demands of pharmaceutical and biotechnology
processing. Depending on your needs, the tube
inside the casing can be “multi-use” or “single-
use.” In multi-use applications, the tube can be
thoroughly cleaned and sterilized between runs and
re-used many times. In single-use strategies, the
tube is disposed of after each process, and a new
tube assembly is used for each batch. This prevents
any possibility of cross-contamination and simplifies
cleaning, maintenance, and validation procedures.
DISADVANTAGES
• Limited maximum flow rate compared
with many other pumps.
• Tubing will degrade or wear over time
requiring periodic replacement.
• Moderate pulsation, particularly with
high viscosity fluids at low rotational
speeds.
• Effectiveness is limited by fluid viscosity.
ADVANTAGES
• Gentle handling of shear-sensitive fluids.
• Excellent for viscous and aggressive
fluids.
• Tubes can be easily cleaned and
sanitized for multi-use.
• Single-use of tubing eliminates
contamination concerns.
• Requires limited maintenance.
• Design prevents backflow and siphoning
without using valves.
• Accurately controllable flow. Ideal for
metering applications.
ADVANTAGES & DISADVANTAGES
OF PERISTALTIC PUMPS
10. ECCENTRIC DISC PUMPS
The eccentric disc pump uses a unique pumping
design that can be very effective for some
applications. Its pumping action is created by a
pumping disc which is mounted on an eccentric
shaft inside a cylinder. As the shaft rotates, the offset
disc creates chambers that alternately increase
and decrease in size. As the chamber enlarges on
the inlet side, product is drawn into the pump. As
the chamber decreases in size on the outlet side,
product is forced out of the pump.
This design has been used in Europe for many years
and is gaining popularity in the U.S. because of its
gentle product handling, leak-free design, and low
maintenance. Eccentric disk pumps also feature
a seal-free design, which eliminates leakage and
reduces maintenance time.
DISADVANTAGES
• Low viscosity fluids can “slip” at high
output pressures, reducing efficiency.
• Typically driven with motor/gear reducer
unit creating large footprint.
• Cannot be shut off without recirculation.
• Moderate flow and pressure pulsation.
• Requires maintenance of two
mechanical seals.
• Some rotor styles may contact the
casing causing particulate shedding.
• Initial cost is typically higher than
centrifugals.
ADVANTAGES
• Ideal for high viscosity fluids.
• Can be used as a metering pump due to
its accurate, consistent output.
• Gently handles shear sensitive fluids and
fluids containing soft or fragile solids.
• Available with hygienic design and
traceability options for high-purity
applications.
• Flow output is unaffected by changes in
head pressure.
• Reversible direction of flow.
• Output can be controlled by varying
drive speed.
• Good suction lift capacity and can be
self-priming if wetted.
ADVANTAGES & DISADVANTAGES
OF ECCENTRIC PUMPS
POSITIVE DISPLACEMENT PUMPS
PUMP BUYING GUIDE
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11. PUMP PERFORMANCE CURVES
The most important link between your specific
application factors and proper pump selection is
the manufacturer’s pump performance curves.
Publishedbythepumpmanufacturer,theyaccurately
predict how a particular pump will perform in varying
conditions.
The composition of the performance curve varies
from manufacturer to manufacturer, but they
generally include most of the performance data you
need to begin sizing your pump, including:
PUMP PERFORMANCE & APPLICATION FACTORS
• Pump model
• Pump speed
• Connection sizes
• Impeller size range
• Rotor material & design
• Head range
• Flow range
• Power requirement
• Efficiency
• NPSHr
It would be nearly impossible for pump
manufacturers to create separate performance
curves for every possible viscosity and temperature
variable, so centrifugal curves are typically based on
pumping water (1 cP) at a given temperature (usually
68-70° F). You can then calculate corrections if
your fluid characteristics vary. Rotary lobe pump
curves typically allow you to plot multiple viscosities
at multiple head pressures within a particular
temperature range.
With the performance curves and pump sizing
software, your pump system expert will be able to
select a pump based on the best efficiency point
(BEP) as well as the optimum impeller diameter and
speed required. For a PD pump application, they will
determine the appropriate rotor design and speed.
A typical PD pump curve is 4 different curves in 1:
1. Capacity as a function of speed, related to
pressure and viscosity.
2. Power as a function of speed, related to pressure
and viscosity of 1 cSt.
3. Power as a function of viscosity greater than 1 cSt
4. Speed as a function of viscosity.
APPLICATION FACTORS
Centrifugal and positive displacement pumps are
both well-suited for high-purity processing, and
there is even some application overlap when it
comes to choosing one or the other. To choose the
right one, it is essential to balance the relationships
between several application factors.
In a perfect world, all of your necessary application
data would be available and accurate before
beginning the pump sizing process, but the truth is
that sometimes much of that information just can’t
be known or isn’t available. This is where your pump
system expert can be a valuable asset. They will
draw on years of application experience to fill in
some of the unknown knowledge gaps during the
sizing and selection process. Eventually, however,
all of the application factors must be confirmed to
ensure that your pump selection, installation, and
operation are successful.
Below are just some of the application factors that
need to be considered.
DOCUMENTATION
In high-purity applications most processors won’t
consider a pump unless proper documentation
ensures full traceability of all product contact parts.
This report will typically include:
• Pump serial/item number
• Declaration of compliance
• Product specification list
• Material test reports & certificates
PERFORMANCE DATA
The characteristics that help define what your pump
needs to do.
• Flow rate (capacity) required
• Suction condition (flooded, suction lift, NPSHa, etc.)
• Discharge head/pressure required
• System pressure
12. PUMP PERFORMANCE & APPLICATION FACTORS
FLUID DATA
The essential information about the liquid you need
to transfer.
• Viscosity
• Density/specific gravity
• Temperature
• Shear sensitivity
• Vapor pressure
• Material compatibility
• Solids content (size & concentration)
• Fluid behavior (Newtonian, etc.)
• Fluid type (hazardous, toxic, abrasive, etc.)
• Cleaning requirement
Among the many factors that influence pump
selection and performance, flow requirements,
pressure requirements, and fluid characteristics are
at the top of the list.
FLOW REQUIREMENTS
Knowing your flow rate requirement is a must for
pump sizing. It is one of the two primary factors for
evaluating a performance curve. If your flow rate
requirement isn’t already a known value dictated
by your process, it can be easily determined. Since
flow is measured as volume over time, you need to
know how much fluid you need to transfer (volume)
and how long you have to transfer it (time).
EXAMPLE: YOU NEED TO TRANSFER 1000 GALLONS
OF FLUID IN 20 MINUTES; 1000 ÷ 20 = 50 GPM.
Once you have determined your flow requirement,
you can locate it on the “X” axis on the performance
curve for any pump to determine if it has the capacity
to suit your needs. Flow can be represented by any
measure of volume over any increment of time, but
most performance curves use gallons per minute
(gpm), liters per minute (lpm), or cubic meters per
hour (m3/h).
Another consideration of flow is the velocity of the
fluid in the piping. Unless process requirements or
fluid characteristics dictate otherwise, a general
speed limit for process fluid velocity is around
5-7 feet per second (fps). The velocity of flow is
determined by the inside dimension of the piping
it flows through, so review the diameters of all
process piping downstream from the pump. Fluid
speeds above 5 fps can contribute to water hammer
and increase friction losses, so make any necessary
piping changes to be sure your fluid velocity is at an
acceptable level.
Also, be aware that the fluid will demonstrate
characteristics of one of the three flow types as it is
traveling through the piping:
• Laminar flow – smooth, streamlined flow with
little disruption of the fluid.
• Transitional flow – fluid demonstrating
characteristics of both laminar and turbulent flow.
• Turbulent flow – chaotic, disorderly fluid action
characterized by eddies and lateral mixing.
The type of flow you have can be indicated by
the Reynolds number, a dimensionless number
that is calculated using factors such as flow rate,
pipe diameter, speed, viscosity, and density.
Excessive turbulent flow could affect your system’s
performance and even impact the product, so
it may be worthwhile, particularly in high-purity
applications, to ask your pump system expert to
calculate the Reynolds number.
PUMP BUYING GUIDE
12
13. PRESSURE REQUIREMENTS
Pressure, or head, is the other primary factor when
evaluating a performance curve. Pressure refers
to the amount of force per unit area (usually psi),
and head is a reference to the height of a column
of water exerting downward pressure (usually in
feet or meters). Head is commonly used instead
of pressure when discussing a centrifugal pump
since the pump’s ability to push against resistance
varies with the fluid’s specific gravity. Both terms
are common in pump discussions and each can be
converted to the other (1psi = 2.31 feet of head).
Two major pressure considerations impact your
pump’s performance: inlet pressure and discharge
pressure. Both must be considered to establish your
system requirements.
Inlet Pressure
The fluid conditions at the inlet of the pump are often
overlooked but are crucial to pump performance.
Inlet pressure is the absolute pressure of the fluid
as it is entering the pump. Insufficient fluid pressure
at the inlet of the pump can cause cavitation, which
reduces pump performance and could potentially
damage the pump.
The amount of inlet pressure required by a particular
pump is published in its performance curve and is
referred to as net positive suction head required
(NPSHr). The amount of pressure that is available
to supply the pump, known as net positive suction
head available (NPSHa), is a function of your piping
system design upstream from the pump. Make sure
your inlet pressure is below the published maximum
inlet pressure limit established by the pump
manufacturer yet high enough to meet the pump’s
NPSHr. Your pump system expert can evaluate
your upstream piping to ensure that it is providing
flooded suction conditions to your pump.
Discharge Pressure
The pressure of the fluid as it leaves the pump is the
discharge pressure. The discharge pressure of the
pump must be sufficient to overcome the resistance
(head) created by your piping system downstream
from the pump. Your pump system expert can
determine your system head by calculating the
vertical distance the fluid must travel, the friction
losses created by the fluid traveling through the
piping, and the specific gravity of the fluid. Once you
have your system head requirement, you can locate
that point on the “Y” axis of any performance curve.
14. FLUID CHARACTERISTICS
It is important to know and understand the
characteristics of the fluid you are pumping. Many
of the choices you will make regarding pump
selection are driven by the physical qualities of your
product. The following are some of the major fluid
characteristics to consider when selecting a pump.
Viscosity
Technically, the viscosity of a fluid is its resistance
to shear or flow when a force is applied to it, an
important factor in pump selection. Informally, it
is referred to as the fluid’s “thickness.” The more
viscous (thicker) a fluid is, the less it tends to flow.
The viscosity of a fluid may not always be constant,
however. Two major factors can influence the
viscosity of a fluid.
• Temperature – viscosity of a fluid decreases
when its temperature increases. This change is
small for some fluids and significant for others.
For example, chocolate syrup is very thick
when it is cold, but it is much thinner when it’s
heated. The viscosity of water, on the other
hand, changes very little with fluctuations in
temperature. So when determining a fluid’s
viscosity, consider the temperature at which the
fluid will be transferred.
• Shear – the mechanical action inside the fluid
chamber of a running pump imparts shear
forces on the liquid. Depending on the type
of fluid, shear forces may change the fluid’s
viscosity. Shear is typically quite high for most
centrifugal pumps and generally less severe for
most PD pumps.
The viscosity of a fluid when it is not exposed to
shear is known as kinematic viscosity. The viscosity
of a fluid when it is under shear is called dynamic
viscosity. Newtonian fluids like water or alcohol
are unaffected by shear. Non-Newtonian fluids like
toothpaste or ketchup may become significantly
more or less viscous when exposed to shear. Make a
point to identify your fluid’s viscosity characteristics
before selecting or sizing a pump. In many cases,
your pump system expert can have a sample of your
product tested to determine the dynamic viscosity.
Viscosity can be expressed in several ways, but
centipoise(cP)iswidelyusedandgenerallyaccepted
by most engineers and pump manufacturers
because it factors in specific gravity of the fluid.
Centrifugal pumps are considered the pump of
choice for lower viscosity fluids in high-purity
applications. By their design, centrifugal pumps must
accelerate the fluid to transfer it, so less viscous
fluids like water (1 cP) are much easier to move in
this way than fluids with a higher viscosity. While
many top quality centrifugal pumps are capable of
pumping products with viscosities up to 1000 cPs
(or roughly the equivalent of 60 weight motor oil),
a centrifugal pump’s efficiency begins to decline
significantly when the fluid viscosity reaches about
250 cPs. Energy requirements also start to increase
drastically as the pump requires more energy to
accelerate the thick fluid. Pump applications for
fluids with viscosities above 250 cPs may be better
suited for a PD pump.
Positive displacement pumps excel at transferring
highlyviscousfluids,upto1millioncPsinsomecases.
But they are also very capable of transferring fluids
as thin as 1 cP. The issue some PD pumps have with
thin fluids is a phenomenon known as “slip.” When
using a rotary lobe pump, for instance, to transfer
a low viscosity fluid against high head pressure, a
small amount of fluid is forced back through the
rotor clearances from the high pressure (discharge)
side to the low pressure (suction) side of the pump.
Slip reduces the pump’s efficiency and diminishes
the amount of pressure the pump can generate, but
it can easily be compensated for with an increase
in pump speed or by selecting rotors with tighter
clearances. When transferring high viscosity fluids,
slip is diminished regardless of the rotor clearances.
PUMP PERFORMANCE & APPLICATION FACTORS
PUMP BUYING GUIDE
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15. Solids Concentration
If fluid contains solid, undissolved particles
suspended in a solution, consider the impact that
each pump style could have on those solids.
Most centrifugal pumps can handle small solids in
moderate to low concentrations, but the high-speed
mechanical action inside the pump casing may
compromise the integrity of the solids.
Generally, PD pumps are more suited to transferring
suspended solids. For rotary lobe pumps, the rotor
size and design are typically the limiting factors for
particle size. Diaphragm pumps can easily handle
large particle sizes, limited only by their piping
and port sizes. Most PD pump manufacturers will
publish the maximum particle size capacity for each
pump size.
TABLE 2 OUTLINES WHICH PUMPS ARE SUITABLE
FOR WHICH TYPE OF PRODUCT.
Shear Sensitivity
Pharmaceutical and biotech fluids can run the full
spectrum when it comes to sensitivity to shear
forces. Some products like water-for-injection,
peptides, or small proteins are relatively unaffected
HIGH
VISCOSITY
LOW
VISCOSITY
HIGH SOLIDS
CONCENTRATION
LOW SOLIDS
CONCENTRATION
KINETIC PUMPS
Centrifugal ✓ ✓
Self-priming ✓ ✓
POSITIVE DISPLACEMENT PUMPS
Rotary Lobe ✓ ✓ ✓
Diaphragm ✓ ✓* ✓
Peristaltic ✓ ✓
Eccentric Disc ✓ ✓ ✓* ✓
TABLE 2
* Unable to pump product of large size and abrasion. Confirm with your pump system expert your application will work with this type of pump.
by shear. Others, like mammalian cells, can be very
sensitive and will require gentle handling.
Centrifugal pumps generate a significant amount of
shear, so they typically are not a good fit for more
sensitive or fragile products.
PD pumps generally handle products more gently
than centrifugals. Larger sized peristaltic pumps
running at low speeds offer minimal product shear.
Rotary lobe and diaphragm pumps are very gentle
for most applications, especially at lower speeds.
Specific Gravity / Density
For calculating friction losses, horsepower
requirements, and some other critical sizing
information, it is very helpful to know the density
or specific gravity of your fluid. Most pump sizing
calculations can be done using either specific
gravity or density. Density is the fluid’s mass per
unit of volume, often expressed as pounds per
cubic foot (lb/ft3) or pounds per gallon (lb/gal). The
specific gravity of your fluid is the ratio of its density
compared to the density of water, expressed as a
dimensionless number. For example, a specific
gravity of 1.12 would indicate a density 1.12 times the
density of water.
16. Temperature
Determine the operating temperatures of all fluids
that will go through your pump system, including
clean-in-place solutions as well as product fluids.
This temperature data will influence your selection
of seals, elastomers, and other materials of
construction. Check the manufacturer’s published
temperature range for your selected pump to be
sure your operating temperatures are within the
limits of the pump.
Temperature also has a direct impact on the fluid’s
vapor pressure. As fluid temperature rises, its vapor
pressure increases, which increases the chance
of cavitation. Your pump system expert will be
able to compensate for temperature factors when
calculating your NPSHr. For rotary lobe pumps,
the fluid temperatures determine rotor clearance
selection. As the pump’s wetted parts expand under
heat, the rotor and casing clearances begin to
shrink. Select rotors that are properly undersized to
keep them from contacting the casing or front cover
as they expand.
Abrasiveness or Stickiness
Fluids that have a particularly abrasive or sticky
nature can have a detrimental effect on the
performance of some other pump types. Abrasive
particles, particularly in a centrifugal pump, can
compromise the internal surface finish and cause
mechanical seal faces to prematurely wear and
leak. Sticky fluids tend to build up on seal faces and
cause leaking. A number of single- and double-flush
seals can mitigate the problems created by these
types of fluid.
MECHANICAL SEALS AND
ELASTOMER REQUIREMENTS
If you don’t already know your seal and elastomer
requirements, your pump system expert can help
you make the proper choice based on several
variables. Chemical compatibility charts are also
available to help you identify the most appropriate
materials of construction for your application.
Some of the main factors that influence seal and
elastomer selection:
• Fluid temperature & viscosity.
• Characteristics of fluid (sticky, abrasive, suspended
solids, air reactivity, exposure risks, etc.)
• System and pump pressure requirements.
• Product /material compatibility.
• Material Certification Requirements.
Mechanical Seals
Mechanical pump seals are available in a wide
variety of configurations. Below are some common
seal types.
• Single – Simplest shaft seal. For fluids that
lubricate the seal surface and don’t crystallize or
harden. Not meant for extremely high pressure.
Not suitable for applications where the pump
may be run dry.
• Single flushed – Provides fluid to the backside of
the seal surfaces to keep them clean and/or cool
during use. Limits the exposure of the seal to
atmosphere.
• Double flushed – Used for hazardous or highly
viscous fluids. Limits the exposure of the seal to
atmosphere.
Mechanical pump seals are typically composed of
one stationary seal face and one rotating seal face.
The two faces may be made of the same material or
they may be different, depending on the application.
Below are some common seal face material
combinations. Not all of them may be appropriate
PUMP PERFORMANCE & APPLICATION FACTORS
PUMP BUYING GUIDE
16
17. for high-purity applications, so work with your pump
system expert to select the right seal materials.
• Carbon vs stainless steel
• Carbon vs silicon carbide
• Carbon vs tungsten carbide
• Silicon carbide vs silicon carbide
• Tungsten carbide vs tungsten carbide
Elastomers
Your high-purity application may require the pump
elastomers to meet specific standards, so select
elastomers that meet the certification requirements
of your application, such as:
• U.S. Pharmacopeia Class VI Certification (USP
Class VI)
• ASME-BPE Standards
• Title 21 CFR 177.2600 and 177.1550
• Cytotoxicity Criteria
• USDA and 3-A Sanitary Standards
• ISO 9001:2000
• Animal Derived Ingredient Free
• QS-9000:1998
Below are some of the common elastomers used
for pump seals, o-rings and gaskets. Not all of them
may be appropriate for your application, so work
with your pump system expert to select the right
elastomers to meet your needs.
• EPDM – Ethylene Propylene Diene Monomer.
Vulnerable to oils and fats. Acceptable for low-
pressure steam. Available in USP Class VI.
Peroxide cured version is preferred over sulfur
cured. Approx. temp. range: -30°F to 300°F.
• FPM – Fluoroelastomer. Also known as Viton® or
FKM. Resistant to most chemicals. Acceptable for
steam applications. Approx. temp. range: -30°F to
400°F.
• PTFE – Polytetrafluoroethylene. Similar to Teflon®
or FEP. Resistant to most products. Excellent for
steam. Not technically an elastomer, will cold flow
under compression. Often used to encapsulate
elastomers for added resilience. Low extractable
and absorption rate. Approx. temp. range: -100°F
to 500°F.
• Silicone – Resistant to glycols, alcohol, and
ozone. Flexible at low temperatures. Good
for some steam and sanitary water systems.
Available in USP Class VI. Platinum cured version
is preferred over peroxide cured. Approx. temp.
range: -40°F to 450°F.
• Buna – Also known as buna-n, nitrile or NBR. Not
a common choice for high-purity applications.
Vulnerable to acids and ozone. Does not pass
USP Class VI. Approx. temp. range: -30°F to
200°F.
Several proprietary elastomers may be suitable for
your application, depending on the specifics of the
product and process. Discuss these options with
your pump system expert:
• Kalrez®
• Tuf-Flex®
• Chemraz®
• Tuf-Steel®
• GYLON BIO-PRO Plus™
• GYLON BIO-PRO®
18. Absolute Pressure – The total pressure exerted by a fluid,
including atmospheric pressure. It uses perfect vacuum
as a zero reference point. Atmospheric pressure + gauge
pressure = absolute pressure. It is often expressed as
pounds per square inch absolute (psia).
Atmospheric Pressure – The constant force exerted by
the weight of the atmosphere. Measure with a barometer,
it varies with changes in altitude.
Best Efficiency Point (BEP) – The flow at which a pump
operates at its highest efficiency for a given impeller
diameter.
Cavitation – The formation of small vapor-filled bubbles
in fluid, commonly caused in pump fluid chambers when
the pressure drops below the vapor pressure of the fluid.
When exposed to high pressure, the bubbles implode
violently creating audible shock waves and potential
damage to the casing and impeller.
Centipoise (cP) – A unit of measure for dynamic
fluid viscosity. It is the kinematic viscosity of a fluid (in
centistokes) multiplied by the density of the fluid.
Centistokes (cSt) – A unit of measure for kinematic fluid
viscosity.
Centrifugal – An inertial force that acts on objects in a
rotation environment, moving them out from the center
of the rotation. Also, a reference to a pump category that
employs this force to transfer fluid.
CIP – Acronym for “Clean In Place.” A process for
automatedly cleaning process piping and equipment
in place without disassembling the system. Done by
pumping cleaning solution through the piping.
Density – The measure of a fluid’s mass per unit of volume.
Often expressed as grams per cubic centimeter (g/cm3).
Dilatant – The term for a fluid whose viscosity increases
as shear increases.
Discharge Pressure – The pressure of a fluid as it is leaving
the discharge port of a pump.
Duty Point – The plotted point at which the pump curve
and the process curve intersect.
DEFINITION OF TERMS
Dynamic Head – The energy required to overcome
resistance and set a fluid in motion.
Eccentric – Not centered or not sharing the same center
axis so as to offset the rotation.
Elastomer – Any rubber-like material that recovers its
original shape after being stretched or compressed.
Flooded Suction – The general condition at the inlet of a
pump in which sufficient positive pressure allows fluid to
flow freely into the pump and avoid cavitation.
Flow Rate – Also referred to as capacity, flow rate is the
volume of fluid that the pump delivers over a given amount
of time. Typically represented as gallons per minute (gpm),
liters per minute (lpm) or cubic meters per hour (m3/h).
Friction Losses – The loss of pressure or head resulting
from the resistance caused by fluid friction against the
piping surfaces as the fluid is flowing. Fiction losses
increase with fluid velocity.
Gauge Pressure – The amount of pressure that exceeds
thesurroundingatmosphericpressure.Itusesatmospheric
pressure as a zero reference point. Absolute pressure -
(minus) atmospheric pressure = gauge pressure. Often
expressed as pounds per square inch gauge (psig).
Head – The height of a column of liquid that represents
a corresponding amount of pressure being exerted at its
base, typically represented in feet. 2.31 feet of head = 1
psi.
Impeller – The rotating pumping element of a centrifugal
pump.
Inlet Pressure – The pressure of fluid as it is entering a
pump.
Kinematic Viscosity – A fluid’s dynamic (or absolute)
viscosity divided by the fluid’s density. It gives an
indication of how fast a fluid will move when a given force
is applied. Usually measured in square centimeters per
second (cm2/s).
PUMP BUYING GUIDE
18
19. Laminar Flow – A type of flow characterized by smooth,
streamlined flow through piping with little disruption of the
fluid. The fluid tends to move through piping in concentric
layers with the highest velocity at the center.
Multi-stage – A type of centrifugal pump with more
than one impeller mounted on the same shaft to create
additional outlet pressure.
Newtonian – A type of fluid whose viscosity does not
change when subjected to shear forces.
NPSHa – Acronym for “Net Positive Suction Head
Available.” The amount of pressure that is available at
the inlet of a pump. It can be calculated by combining
atmospheric pressure with the static head then subtracting
friction losses and the fluid’s vapor pressure.
NPSHr – Acronym for “Net Positive Suction Head
Required.”The minimum amount of pressure required at
the inlet of a given pump to avoid cavitation.
Outlet Pressure – See Discharge Pressure.
Positive Displacement – A category of pumps
characterized by the direct, physical capture and
discharge of controlled volumes of fluid.
Pressure – A measure of force per unit of area, such
as pounds per square inch (psi). In terms of pump
performance, pressure is a way to define how much
resistance the pump can overcome in order to transfer
fluid.
Pulsation – A rhythmic, alternating increase and decrease
of output pressure and/or flow caused by the mechanical
motion of some pumps.
Reynolds Number (Re) – A dimensionless number in fluid
mechanics used to indicate the flow characteristics of a
fluid by calculating the ratio of inertia forces to viscous
forces.
Rotodynamic – The characteristic of changing rotating
mechanical energy into a form of kinetic energy that
creates fluid velocity and pressure.
Rotor – The rotating pumping element of a rotary lobe
pump.
Rouging – A form of visible surface corrosion that can
occur on stainless steel when the passive layer of the
material is compromised.
SIP – Acronym for “Steam in Place” or “Sterilize in Place.”
A process for steam cleaning or sterilizing process piping
and equipment in place without disassembling the system.
Slip – Leakage of fluid through the pump clearances of a
rotary lobe pump from the high-pressure side to the low-
pressure side. Characteristic of low viscosity fluids in a
high head condition.
Specific Gravity – A dimensionless number that
represents the ratio of a fluid’s density to the density of
water.
Suction Lift – Negative pressure on the suction side of
the pump, usually measured in feet, when the fluid level
to be pumped is below the centerline of the pump inlet.
Suction Pressure – See inlet pressure.
Thixotropic – A fluid that decreases in viscosity when
exposed to shear forces.
Transitional Flow – Flow exhibiting characteristics of both
laminar and turbulent flow.
Turbulent Flow – A type of flow characterized by chaotic,
disorderly fluid action through piping.
Vapor Pressure – The pressure at which a fluid changes
to vapor at a given temperature.
Velocity – The distance a fluid moves through piping per
unit of time.
Viscosity – The measure of a fluid’s resistance to shearing
forces or flow.
Water Hammer – An abrupt fluid pressure surge caused
when valves are rapidly opened or closed.
