A GUIDE TO CHOOSING THE

RIGHT PUMP FOR HYGIENIC APPLICATIONS

eBOOK

INTRODUCTION ...................................................................................................................................................................3

PUMP TYPES ..........................................................................................................................................................................3

Kinetic Pumps ...........................................................................................................................................................................3

• Centrifugal ...........................................................................................................................................................................4

• Self-priming ........................................................................................................................................................................5

Positive Displacement ...........................................................................................................................................................5

• Rotary Lobe ..........................................................................................................................................................................6

• Diaphragm............................................................................................................................................................................7

• Peristaltic ..............................................................................................................................................................................8

• Eccentric Disc ......................................................................................................................................................................9

PUMP PERFORMANCE & APPLICATION FACTORS .................................................................................... 10

Pump Performance Curves ................................................................................................................................................. 10

Documentation and Data ..................................................................................................................................................... 11

Flow Requirements ............................................................................................................................................................... 12

Pressure Requirements ....................................................................................................................................................... 13

• Inlet Pressure .................................................................................................................................................................... 13

• Discharge Pressure .......................................................................................................................................................... 13

Fluid Characteristics ............................................................................................................................................................. 14

• Viscosity ............................................................................................................................................................................. 14

• Solids Concentration ....................................................................................................................................................... 15

• Shear Sensitivity ............................................................................................................................................................... 15

• Specific Gravity / Density ............................................................................................................................................... 15

• Temperature ...................................................................................................................................................................... 16

• Abrasiveness or Stickiness ............................................................................................................................................ 16

Mechanical Seals & Elastomer Requirements ............................................................................................................... 16

• Mechanical Seals .............................................................................................................................................................. 16

• Elastomers .......................................................................................................................................................................... 17

DEFINITION OF TERMS ................................................................................................................................................. 18

TABLE OF CONTENTS

PUMP BUYING GUIDE2

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 TYPESThe 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 PUMPSPumps 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.

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 GUIDE4

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 PUMPSA 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 PUMPSMembers 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.

ROTARY LOBE PUMPSRotary 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 GUIDE6

DIAPHRAGM PUMPSAir operated diaphragm (AOD) or double-diaphragm (AODD) pumps (sometimes referred to as “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

TWIN SCREW PUMPSTwin 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 GUIDE8

PERISTALTIC PUMPSIn 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

ECCENTRIC DISC PUMPSThe 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 GUIDE10

PUMP PERFORMANCE CURVES The most important link between your specific application factors and proper pump selection is the manufacturer’s pump performance curves. Published by the pump manufacturer, they accurately 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.

DOCUMENTATIONIn 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 DATAThe 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

PUMP PERFORMANCE & APPLICATION FACTORS

FLUID DATAThe 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 GUIDE12

PRESSURE REQUIREMENTSPressure, 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.

FLUID CHARACTERISTICSIt 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) is widely used and generally accepted 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 highly viscous fluids, up to 1 million cPs in some cases. 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 GUIDE14

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.

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

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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®

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 the surrounding atmospheric pressure. It uses atmospheric 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).

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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.

Purchasing a pump can be overwhelming, but once you’ve answered these four specifications, you will be ready to make a decision. First, determine the flow rate. This measures how much fluid is moving and how fast through your process system. Typically represented as gallons per minute (gpm), liters per minute (lpm) or cubic meters per hour (m3/h). See page 12 to determine Flow Rate.

Second, determine pressure or head. A measure of force per unit of area, such as pounds per square inch (psi). In terms of pump performance, pressure is

NEXT STEPS

Central States Industrial Equipment (CSI) is a preferred source for hygienic pipe, valves, fittings, pumps, heat exchangers, and MRO supplies for industrial processors. With four distribution facilities across the US, CSI provides fast and reliable fulfillment for industrial parts and equipment needs.

CSI also provides detail design and execution for hygienic process systems in the food, dairy, beverage, pharmaceutical, biotechnology, and personal care industries. Specializing in process piping, system start-ups, and cleaning systems, CSI leverages technology, intellectual property, and industry expertise to deliver solutions to processing problems.

PUMP BUYING GUIDE REV 7/20

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800.654.5635 | 417.831.1411

a way to define how much resistance the pump can overcome in order to transfer fluid. See page 13 to determine pressure or head. Third, determine what the fluid is and its characteristics; what is the application?. Is it dense? What are the temperature requirements? What is the size of the contents? See page 11.

Fourth, how will the pump be powered? Is it indoors or outdoors?

Starting with these four steps will assist your CSI pump expert in helping you select the best pump for your application. CSI is known in the sanitary industry as a marketing leader in the specification, sizing, and supply of pumping technology.

To speak with a Pump expert call 417.831.1411 or email pumps@csidesigns.com

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