Selecting a hygienic pump is about much more than matching a flow rate. While many engineers and maintenance professionals know how much product they need to move, determining which pump can reliably deliver that performance requires a deeper understanding of pump curves.

A pump performance curve provides a roadmap for understanding how a pump will perform in a specific application. By accurately interpreting the information it contains, engineers can select equipment that meets process requirements, operates efficiently, and delivers long-term reliability. Conversely, misinterpreting a pump curve can lead to oversized equipment, excessive energy consumption, premature component wear, and poor process performance.

Whether specifying a new pump system or troubleshooting an existing installation, understanding how to read a pump curve is an essential skill for anyone involved in hygienic processing applications.

What Is a Pump Curve?

A pump curve is a graphical representation of a pump’s performance characteristics. It illustrates the relationship between flow rate and the amount of head the pump can generate. Manufacturers develop these curves through performance testing and use them to predict how a pump will perform in real-world applications.

The primary purpose of a pump curve is to help users determine whether a specific pump can meet the requirements of a given system. By comparing the process requirements to the pump’s performance characteristics, engineers can identify the most appropriate pump model, impeller diameter, and operating speed.

While pump curves may initially appear complex, they are simply visual tools that communicate how a pump behaves across its operating range.

Understanding the Key Components of a Pump Curve

Most centrifugal pump curves include several pieces of information that help evaluate pump performance.

The horizontal axis typically represents flow rate, often displayed in gallons per minute (GPM) or cubic meters per hour (m³/h). As flow increases, the operating point moves to the right on the curve.

The vertical axis represents head, usually expressed in feet or meters. Head is a measure of the energy imparted to the fluid and is closely related to the Total Dynamic Head (TDH) requirements of the system.

The main performance curve shows the relationship between flow and head. In centrifugal pumps, head generally decreases as flow increases. This characteristic creates the familiar downward-sloping shape seen on most pump curves.

Many pump curves also include efficiency contours. These lines indicate how efficiently the pump converts mechanical energy into fluid movement at various operating points. Operating near the highest efficiency region can reduce energy costs while improving reliability and component life.

Additional information may include brake horsepower requirements, NPSHr values, and impeller diameter options. Together, these data points provide a complete picture of pump performance.

Start with the System Requirements

Before looking at any pump curve, it is important to understand the process requirements.

The most critical inputs are the required flow rate and Total Dynamic Head. These values define the operating conditions the pump must achieve. Additional considerations may include fluid viscosity, temperature, solids content, shear sensitivity, and available suction conditions.

Many pump selection issues arise because users focus solely on flow rate. Two systems may require identical flow rates but vastly different head requirements. A pump that performs well in one application may be completely unsuitable for another.

This is why accurately calculating Total Dynamic Head is such an important first step in the pump selection process.

Finding the Duty Point

Once the system requirements are known, the next step is identifying the duty point.

The duty point is the location where the required flow rate intersects the required Total Dynamic Head on the pump curve. This point represents where the pump must operate to satisfy the application’s demands.

For example, if a system requires 150 GPM at 80 feet of TDH, locating those values on the curve reveals whether a particular pump can achieve the desired performance.

If the duty point falls directly on or near the pump’s performance curve, the pump may be a suitable candidate. If the duty point lies above the curve, the pump will be unable to generate the required head at the desired flow rate. If the duty point falls significantly below the curve, the pump may be oversized for the application.

The goal is not simply finding a pump that can reach the duty point. The objective is finding a pump that can operate efficiently and reliably at that point.

Why Best Efficiency Point Matters

One of the most important concepts in pump selection is the Best Efficiency Point (BEP).

The BEP represents the operating condition where the pump achieves its highest hydraulic efficiency. At this point, internal hydraulic forces are balanced, vibration levels are minimized, and energy losses are reduced.

Operating near the BEP often results in lower operating costs and longer equipment life. Mechanical seals, bearings, shafts, and other components generally experience less stress when the pump is operating in this optimal region.

When a pump operates too far left or right of its BEP, efficiency decreases and reliability can suffer. Excessive vibration, recirculation, heat generation, and increased maintenance requirements are common symptoms of operation outside the preferred range.

This is one reason oversized pumps frequently create problems. Although they can meet system requirements, they often operate far from their optimal efficiency range.

Understanding System Curves

One of the most common misconceptions in pump selection is the belief that a pump will always operate exactly at the duty point selected on the curve.

In reality, pumps operate where the pump curve intersects the system curve.

The system curve represents the resistance created by the piping system. As flow increases, friction losses increase, causing the required head to rise.

When the pump curve and system curve are plotted together, the intersection of these two curves becomes the actual operating point. Any changes to the system, such as valve adjustments, piping modifications, or filter fouling, can shift the system curve and alter pump performance.

Understanding this relationship helps explain why actual field performance sometimes differs from initial design expectations.

Accounting for Viscosity and Product Characteristics

Centrifugal pump curves are generated using water as the test medium. However, hygienic processing applications often involve fluids that behave very differently.

Products such as yogurt, creams, sauces, chocolate, syrups, and concentrates can have significantly higher viscosities than water. As viscosity increases, centrifugal pump performance can change substantially.

Higher viscosity typically reduces flow capability while increasing power requirements. Ignoring viscosity corrections can result in selecting a pump that appears suitable on paper but fails to deliver the required performance in practice. Most centrifugal pump selection programs include a viscosity adjustment tool to account for the effects of viscosity and specific gravity on the pump performance curve.

Product sensitivity should also be considered. Some products are susceptible to shear damage, particle degradation, or texture changes. In these situations, selecting a pump involves more than simply meeting hydraulic requirements.

Understanding both the process fluid and the pump’s operating characteristics is essential for achieving optimal performance.

Common Pump Curve Mistakes

Many pump selection challenges can be traced to a few common mistakes.

One frequent error is selecting a pump solely based on maximum flow capacity rather than actual operating requirements. Another is overlooking Total Dynamic Head calculations or failing to account for future system changes.

Some users ignore efficiency considerations and focus only on achieving the required flow and pressure. Others neglect viscosity corrections or fail to evaluate NPSH requirements, increasing the risk of cavitation and reduced pump life.

Perhaps the most common mistake is assuming that bigger is always better. While oversized pumps may appear to provide additional safety margin, they often create unnecessary energy consumption, reduced efficiency, and increased maintenance costs.

Pump Curves Are Only Part of the Selection Process

Pump curves are among the most valuable tools available for pump selection, but they should not be viewed in isolation.

Successful pump selection requires understanding the complete application, including flow rate, Total Dynamic Head, fluid properties, operating conditions, product sensitivity, and future process requirements. When these factors are considered together, pump curves become powerful tools for selecting equipment that delivers reliable, efficient performance for years to come.

For hygienic processing applications, working with experienced application engineers can help ensure that all aspects of the process are evaluated. A properly selected pump not only meets today’s requirements but also supports long-term operational reliability, product quality, and overall process efficiency.

If you need assistance selecting a hygienic pump for your application, contact your local Fristam distributor or one of our application engineers for guidance.

Protecting Your Pump During CIP, SIP, and Temperature Transitions

Positive displacement pumps are widely used throughout the food, beverage, dairy, pharmaceutical, and personal care industries because of their gentle product handling, accurate flow control, and ability to process a wide range of viscosities.

While many engineers focus on flow rate, pressure, and product characteristics when selecting a pump, temperature changes within the process can be just as important. Rapid transitions between product temperatures and cleaning temperatures can create significant thermal expansion or contraction inside the pump, potentially resulting in costly damage if the proper rotor design is not selected.

This is where hot clearance rotors become an important consideration.

What Are Hot Clearance Rotors?

Hot clearance rotors are specially machined positive displacement pump rotors designed with additional internal clearances to accommodate thermal expansion during high-temperature cleaning or steaming operations, or a rapid change to a cold process after cleaning.

As temperatures increase, the metal components inside the pump naturally expand, or contract as they cool. This includes the shaft, rotors, pump housing, and cover. Because hygienic positive displacement pumps operate with extremely tight internal clearances to maximize efficiency, even small amounts of thermal changes can significantly reduce the available running clearance between rotating and stationary components.

Without sufficient clearance, thermal expansion/contraction can cause:

• Rotor-to-cover contact
• Rotor-to-housing contact
• Increased wear
• Reduced pump life
• Product contamination from metal-to-metal contact
• Costly repairs and downtime

Hot clearance rotors help prevent these issues by providing additional space for thermal movement during process temperature changes.

Why Temperature Differential Matters

The primary concern is not necessarily the operating temperature itself, but rather the temperature differential the pump experiences.

For example, consider a process where:

• Product temperature = 50°F
• CIP solution temperature = 180°F

This creates a temperature differential of 130°F.

When a cold pump is suddenly exposed to significantly hotter cleaning solutions, the internal components begin expanding. Or the opposite in a cooling situation.  If the temperature change is severe enough, the expansion can exceed the available internal clearances designed into the pump.

Because Fristam FKL pumps are manufactured with extremely tight internal clearances, selecting the proper rotor configuration is essential when large temperature swings are present.

Recommended Rotor Selection Guidelines

Fristam recommends selecting rotors based on the maximum temperature differential expected between product processing and cleaning or steaming operations.

Temperature Differential (ΔT)	Recommended Rotor
Up to 140°F	Standard Rotors
Up to 210°F	High Temperature (Hot Clearance) Rotors

 

In the earlier example of a 50°F product and 180°F CIP solution, the 130°F temperature differential falls within the operating range of standard rotors.

However, applications involving hotter cleaning cycles, steam sterilization, or larger temperature swings may require high-temperature rotors to protect the pump from thermal expansion-related damage.

Common Applications for Hot Clearance Rotors

Hot clearance rotors are commonly specified in applications that experience frequent or extreme temperature transitions, including:

Steam-In-Place (SIP) Systems

Pharmaceutical and biotechnology processes often utilize steam sterilization temperatures that can create significant thermal expansion inside the pump. Hot clearance rotors help ensure reliable operation throughout these sterilization cycles.

High-Temperature CIP Programs

Many food, dairy, and beverage facilities use elevated-temperature cleaning solutions to improve cleaning effectiveness. Repeated exposure to hot CIP cycles can create thermal stresses that justify additional rotor clearance.  Also, if the pump is running above 150-200 rpm for CIP, the hot CIP can flash in standard clearance configuration, so the slightly larger clearance can alleviate the potential for flashing.

Batch Processing Operations

Facilities that frequently switch between refrigerated products and hot cleaning solutions often experience the largest temperature differentials and may benefit from high-temperature rotor configurations.

Seasonal Processing Environments

Applications operating in cold production areas followed by hot cleaning cycles can experience larger-than-expected temperature transitions that should be evaluated during pump selection.

Balancing Efficiency and Thermal Protection

It is important to understand that rotor clearances directly influence pump efficiency, mainly on products below 200 cps viscosity.

Standard rotors provide the tightest internal clearances and typically deliver the highest volumetric efficiency. For this reason, standard rotors should be used whenever temperature conditions allow.

The goal is to select the rotor configuration that provides adequate thermal protection without introducing unnecessary clearance.

When Should You Specify Hot Clearance Rotors?

Consider discussing hot clearance rotors with your pump supplier if:

• Your process includes steam sterilization.
• CIP temperatures exceed normal operating temperatures by a significant margin.
• The pump is running above 150-200 rpm during hot CIP.
• Products are refrigerated or processed at low temperatures prior to cleaning.
• The pump experiences frequent thermal cycling.
• Previous pumps have shown signs of rotor or housing contact after cleaning cycles.

Evaluating temperature differential during the pump selection process can help prevent unexpected wear and extend equipment life.

The Importance of Application Review

Every process is unique. Product temperature, cleaning temperature, cleaning frequency, pump size, operating conditions, and process requirements all influence whether standard or high-temperature rotors are appropriate.

For this reason, Fristam recommends reviewing operating and cleaning conditions during pump selection to ensure the proper rotor design is specified from the start.

A simple evaluation of temperature differential can help protect the pump, reduce maintenance costs, and maximize long-term reliability.

When it comes to positive displacement pumps, proper clearances matter—and selecting the correct rotor configuration is one of the simplest ways to prevent costly thermal expansion damage before it occurs.

Talk to a Hygienic Pumping Expert

Not sure whether your application requires standard or high-temperature rotors? Your local authorized Fristam distributor or Fristam application expert can help evaluate your process conditions, temperature differentials, and cleaning procedures to ensure the proper pump configuration is selected for maximum reliability and service life.

Selecting the right hygienic pump starts long before reviewing performance curves or comparing pump models. One of the most important steps in the process is understanding Total Dynamic Head (TDH).

Whether transferring milk, yogurt, sauces, pharmaceutical solutions, cleaning chemicals, or personal care products, every pumping system creates resistance that the pump must overcome. Understanding this resistance is essential for selecting a pump that delivers the required flow rate while operating efficiently and reliably.

Unfortunately, TDH is often misunderstood or overlooked during the pump selection process. When this happens, the result can be excessive energy consumption, reduced pump efficiency, premature seal wear, and costly downtime.

For engineers and maintenance professionals involved in system design or equipment upgrades, understanding TDH is one of the most valuable skills for ensuring long-term pumping performance.

What is Total Dynamic Head?

Total Dynamic Head represents the total resistance a pump must overcome to move a fluid through a system at a specified flow rate. It is typically expressed in feet or meters of head and serves as one of the primary inputs used for pump selection.

Simply put, TDH answers the question:

“How much energy must the pump provide to move the required amount of fluid from one point in the process to another?”

Many people assume TDH refers only to the vertical height a fluid must be lifted. While elevation changes can contribute to TDH, they are only one part of the equation. In many hygienic processing systems, friction losses throughout the piping network actually represent the largest portion of the total head requirement.

Understanding all of the factors that contribute to TDH is critical to selecting the correct pump for the application.

The Components of Total Dynamic Head

TDH is generally calculated by combining three primary elements: static head, friction losses, and pressure losses created by equipment within the system.

Static Head

Static head is the difference in elevation between the fluid source and destination.

If a product must be pumped to a higher elevation, additional energy is required to overcome gravity. For example, transferring product from a floor-level process vessel to a filler located on an elevated platform requires more head than transferring between tanks located at the same elevation.

Static head remains relatively constant regardless of flow rate and is often the easiest portion of the calculation to determine.

Friction Losses

As fluid travels through piping, energy is lost due to friction between the fluid and the internal surfaces of the piping system.

The amount of friction loss depends on several factors, including pipe diameter, pipe length, flow rate, fluid viscosity, and the overall design of the piping network.

One important concept often overlooked is that friction losses increase significantly as flow rates increase. Doubling the flow rate does not simply double system resistance—it can increase friction losses dramatically depending on system conditions.

This relationship is one reason why pump selection should never be based on flow rate alone.

Check out Fristam’s Friction Loss Calculator

Equipment and Component Losses

Every component installed in a process line creates additional resistance.

Valves, elbows, tees, heat exchangers, filters, flow meters, spray devices, and other equipment all contribute to the total head requirement. While each component may create only a small pressure drop individually, the cumulative effect can be substantial.

In many hygienic processing systems, these losses represent a surprisingly large percentage of the overall TDH.

Ignoring them during pump sizing can result in pumps that fail to achieve the desired operating point once installed.

Why Viscosity Plays a Major Role

The properties of the fluid being pumped have a direct impact on Total Dynamic Head.

As viscosity increases, friction losses throughout the system also increase. A piping system that performs well when handling water may require significantly more head when pumping yogurt, syrup, cream, concentrates, or other viscous products.

Viscosity can also change during production as temperatures fluctuate or product formulations vary. These changes can alter system resistance and impact pump performance.

This is why accurate fluid property information is one of the most important inputs when evaluating a hygienic pumping application.

Why TDH Changes During Production

Many engineers assume TDH remains constant once a system is designed. In reality, operating conditions often change throughout production.

Tank levels rise and fall. Filters gradually become loaded with product. Process equipment is added or modified over time. Product viscosities may change due to temperature fluctuations or formulation differences.

Cleaning processes can create another challenge. A pump selected for transferring a viscous product may also be expected to handle water-like cleaning solutions during CIP operations. These dramatically different conditions can create very different operating requirements.

Understanding how TDH changes during both production and cleaning cycles helps ensure the selected pump can perform reliably across all operating conditions.

Common TDH Calculation Mistakes

Many pump performance issues can be traced back to assumptions made during the sizing process.

One common mistake is focusing only on elevation changes while overlooking friction losses and equipment losses. Another is using water-based calculations for highly viscous products.

Future expansion requirements can also lead to oversized pump selections. While planning for growth is important, selecting a pump significantly larger than current operating requirements often creates efficiency and reliability concerns.

Another frequent issue is relying on estimated piping layouts rather than actual system measurements. Even relatively small changes in pipe diameter, pipe length, or component count can have a meaningful impact on total head requirements.

Accurate information almost always leads to better pump selection decisions.

A Simple TDH Calculation Example

Consider a process application requiring a flow rate of 150 gallons per minute.

The system includes:

• 15 feet of static elevation
• 25 feet of friction loss through piping
• 10 feet of losses through valves and process equipment

The Total Dynamic Head would be:

15 ft + 25 ft + 10 ft = 50 ft TDH

Based on this calculation, the pump must be capable of delivering 150 gallons per minute at 50 feet of Total Dynamic Head.

While this seems straightforward, determining the correct pump requires one additional step.

Using TDH and Flow Rate to Select a Pump

Calculating Total Dynamic Head is not the end of the pump selection process—it is the beginning.

Once the required flow rate and TDH have been determined, these values are used together to evaluate pump performance curves.

A pump curve illustrates how a pump will perform across a range of operating conditions. The horizontal axis typically represents flow rate, while the vertical axis represents total head. By locating the point where the required flow rate intersects the required TDH, engineers can identify pumps capable of meeting the application’s requirements.

However, selecting a pump involves more than simply finding a model that can reach the required operating point.

The ideal pump should operate near its Best Efficiency Point (BEP), where hydraulic efficiency, reliability, seal life, bearing life, and energy consumption are optimized. Pumps operating too far away from their BEP may experience increased vibration, reduced efficiency, higher maintenance costs, and shortened service life.

This is why successful pump selection always begins with an accurate TDH calculation but does not end there.

What Comes After TDH?

Once flow rate and Total Dynamic Head have been established, the next step is understanding how to interpret pump performance curves and identify the optimal operating point for the application.

Partner with Fristam for Pump Selection Support

Every pumping application is unique. Fluid properties, process conditions, cleaning requirements, future expansion plans, and system design all influence pump selection.

Fristam’s application engineering team works with customers every day to evaluate pumping systems, calculate operating requirements, and recommend solutions that maximize performance and reliability.

If you’re designing a new process or looking to optimize an existing system, contact your local Fristam distributor or application engineer for assistance.

Why Viscosity Is One of the Most Important, and Misunderstood Process Variables
When selecting hygienic pumping equipment, flow rate and pressure requirements often receive the most attention. However, one of the most influential factors affecting pump performance is frequently underestimated: viscosity.

Viscosity directly impacts how a product flows through piping systems, how efficiently a pump operates, how much energy is required, and how gently the product is handled during processing. Many pump performance issues can ultimately be traced back to viscosity assumptions that do not accurately reflect real operating conditions.

For hygienic processors handling products ranging from water-like beverages to thick creams, yogurt, sauces, peanut butter, or pharmaceutical formulations, understanding viscosity is essential for achieving reliable and efficient system performance.

What Is Viscosity?
Viscosity is a fluid’s resistance to flow. In simple terms, it describes how “thick” or “thin” a product behaves during processing.

Low-viscosity fluids such as water, alcohol, or CIP solutions flow easily with minimal resistance, while high-viscosity products such as syrups, yogurt, creams, gels, and concentrates require significantly more energy to transfer.

In hygienic processing environments, viscosity can vary dramatically depending on product composition, temperature, solids concentration, entrained air, and mixing conditions. As a result, a product’s viscosity may change substantially throughout the process.

Viscosity is commonly measured using viscometers or rheometers and is typically expressed in centipoise (cP).

To put viscosity into perspective, water at room temperature measures approximately 1 cP. Milk may range from 2–5 cP, while ketchup can exceed 50,000 cP depending on formulation and temperature. Peanut butter and similar products may reach several hundred thousand cP.

Because viscosity can change significantly with temperature and shear conditions, processors should evaluate viscosity under actual operating conditions whenever possible.

Why Viscosity Matters in Pump Selection
Viscosity influences nearly every aspect of pump performance.

As viscosity increases, fluid friction inside piping systems also increases. This creates higher pressure losses, affects flow characteristics, and changes how pumps behave hydraulically.

For centrifugal pumps, increasing viscosity generally reduces flow rate and efficiency while increasing power consumption and heat generation. Higher viscosity can also create more challenging suction conditions, particularly if the system was originally designed for lower-viscosity products.

Positive displacement pump technologies are often better suited for higher-viscosity applications because they can maintain stable flow across a broader operating range while typically providing gentler product handling.

Selecting the wrong pump technology for a given viscosity range can result in unstable flow, excessive shear, increased energy usage, premature wear, and inconsistent process performance.

The Impact of Temperature on Viscosity
One of the most important considerations in hygienic processing is that viscosity is rarely constant.

Many products become dramatically thinner as temperature increases. Chocolate, syrups, sauces, creams, and personal care products may flow very differently at processing temperature compared to ambient conditions.

Conversely, products may thicken significantly during cooling cycles, startup conditions, or intermittent production stoppages.

This creates an important challenge during equipment selection: which viscosity should the pump actually be sized for?

In many applications, pumps must be capable of handling both startup and operating viscosities to ensure reliable performance throughout the process.

Shear Sensitivity and Apparent Viscosity
Some hygienic products behave differently under movement or agitation.

Products such as yogurt, cultured dairy products, gels, sauces, creams, and certain pharmaceutical formulations may temporarily become thinner when exposed to shear forces during pumping or mixing. This behavior is known as shear thinning.

Other products may become thicker when agitated, while some fluids exhibit viscosity changes over time under constant shear. These non-Newtonian behaviors can complicate pump selection because the product’s apparent viscosity changes dynamically during operation.

Understanding how a product responds to shear is especially important when handling delicate or texture-sensitive products where maintaining consistency and product integrity is critical.

Viscosity and Product Integrity
Highly viscous products often require more energy to move through a system. If the wrong pump technology is selected, this additional energy can generate excessive shear, heat, or pressure fluctuations that negatively impact product quality.

Excessive shear may damage particulates, alter texture, reduce protein integrity, destabilize emulsions, or affect final product consistency.

In many hygienic applications, maintaining product integrity is just as important as achieving target flow rates.

Common Viscosity-Related Pumping Challenges
When viscosity is not fully considered during pump selection, processors may encounter several common issues.

High-viscosity products create significantly greater resistance in piping systems, often requiring more pressure than originally anticipated. This can lead to undersized motors, poor flow performance, or excessive energy consumption.

Viscous products may also create difficult suction conditions, particularly when pumps are undersized or installed with long suction piping runs. In severe cases, this can contribute to cavitation or unstable product flow.
Additional friction generated while pumping viscous products can increase product temperature, potentially affecting sensitive formulations, emulsions, or texture-sensitive products.

Cleaning performance is another important consideration. Highly viscous products are often more difficult to remove during CIP cycles, increasing the importance of hygienic pump design, proper line velocities, and effective cleaning procedures.

In applications involving changing viscosity conditions, processors may also experience inconsistent flow behavior if the pump was not properly selected for the full operating range.

Twin screw pumps have become increasingly popular in hygienic applications because they can handle a broad range of viscosities while supporting both product transfer and CIP operations within a single pump.

Looking Beyond Published Viscosity Numbers
One of the most common mistakes in hygienic pump selection is relying solely on a single published viscosity value.

Processors should evaluate viscosity across the full operating window, including startup conditions, temperature changes, shear sensitivity, CIP requirements, batch-to-batch variation, and future product flexibility.

Understanding the complete operating environment helps ensure reliable long-term pump performance under real-world production conditions.

Final Thoughts
Viscosity plays a central role in hygienic pump performance, influencing everything from flow stability and energy consumption to product integrity and cleaning effectiveness.

Because viscosity can change throughout the process — sometimes dramatically — successful pump selection requires a broader understanding of both the product and the operating environment.

By evaluating viscosity alongside shear sensitivity, temperature, CIP requirements, and overall system design, processors can improve reliability, maintain product quality, and reduce long-term operating costs.

To learn more about selecting the right hygienic pump technology for viscous or shear-sensitive applications, contact your local authorized Fristam distributor or connect with one of our application experts.

In hygienic processing applications, maintaining product integrity is often just as important as achieving the required flow rate or pressure. Whether processing dairy products, protein beverages, creams, pharmaceutical ingredients, cultured products, or personal care formulations, many fluids can be sensitive to excessive mechanical stress during transfer. One of the most common causes of product degradation in these systems is shear.

While shear is frequently discussed in processing environments, it is also commonly misunderstood. Many processors assume shear is only associated with high-speed mixing equipment, but pumps themselves can also introduce mechanical forces that affect viscosity, texture, particulate integrity, emulsions, and overall product quality. Understanding how shear develops inside hygienic pumps—and how system design influences it—can help processors improve consistency, reduce waste, and protect sensitive products throughout production.

Shear occurs when layers of fluid move at different velocities relative to one another. As product accelerates through narrow clearances, around impeller surfaces, or through restrictions in the piping system, mechanical energy is transferred into the fluid. Some products tolerate this energy with little effect, while others can experience noticeable changes in structure or performance.

In hygienic applications, shear-sensitive products can include yogurt, cream, cultured dairy products, protein beverages, sauces containing particulates, cosmetic emulsions, nutraceutical formulations, and pharmaceutical media. Excessive shear may lead to broken particulates, reduced viscosity, damaged proteins, destabilized emulsions, or undesirable texture changes. In some applications, the effects are immediately visible. In others, product degradation may only become apparent later in shelf life, appearance, or overall process consistency.

Pump selection plays a major role in controlling these forces. Centrifugal pumps, for example, generate flow through rotational velocity. As impeller tip speed increases, localized shear forces can also increase. In many low-viscosity hygienic applications, centrifugal pumps provide excellent performance with minimal product impact. However, operating conditions matter significantly. Running far away from the pump’s best efficiency point (BEP), excessive throttling, recirculation, or selecting an oversized pump can all contribute to unnecessary fluid stress and increased turbulence within the system.

Positive displacement pumps operate differently by moving a fixed volume of product through the pump with each rotation. Because flow is created mechanically rather than through velocity alone, many PD technologies can provide gentler handling for viscous or delicate products. Twin screw pumps have also gained popularity in hygienic applications because they can combine low-shear product handling with process and CIP functionality in a single unit. Their ability to manage entrained air, maintain smooth flow characteristics, and reduce pulsation can help protect products that may otherwise be affected by aggressive flow conditions.

System design can influence shear just as much as the pump itself. Restrictions in piping, undersized suction lines, abrupt directional changes, excessive differential pressure, and improperly selected valves can all create additional stress on the product. Even a well-designed pump may struggle to provide gentle handling if the surrounding system introduces unnecessary turbulence or pressure fluctuations.

Temperature and viscosity also play an important role. Higher viscosity fluids naturally require more energy to move, which can increase stress if equipment is not properly selected. Some products may also become more shear-sensitive at elevated temperatures or during recirculation. This is particularly important during blending, batching, or extended transfer cycles where the same product repeatedly passes through the pump.

One of the challenges with identifying shear-related issues is that they are not always obvious. A system may appear to operate normally while still gradually damaging product quality over time. Processors may instead observe symptoms such as inconsistent viscosity, changes in texture, separation, reduced yield, or shorter shelf life without immediately connecting the issue back to pump operation or system conditions.

Evaluating shear requires looking beyond flow rate alone. Impeller diameter, rotational speed, pump operating range, product viscosity, system resistance, and piping layout all contribute to how the fluid behaves during transfer. In many cases, selecting a pump specifically designed for gentle handling can improve overall process stability while helping preserve valuable product characteristics.

For hygienic processors, the goal is not simply moving product from one point to another—it is doing so while maintaining consistency, quality, and process reliability. Understanding how shear develops within hygienic pump systems can help processors make more informed equipment decisions and reduce the risk of unintended product damage.

Whether evaluating centrifugal, positive displacement, or twin screw technologies, processors should work closely with experienced hygienic pump specialists to ensure the selected equipment aligns with the unique characteristics of the application. To learn more about selecting the right hygienic pump for sensitive products, contact your local authorized Fristam distributor or connect with one of Fristam’s application experts to discuss your specific process requirements.

Selecting a sanitary centrifugal pump for a hygienic process is often approached as a straightforward exercise in matching flow rate and pressure requirements. While these parameters are essential, they represent only part of the decision. In practice, pump performance is shaped just as much by the characteristics of the product being handled, the design of the system, and the operational expectations placed on the equipment. In food, beverage, dairy, and pharmaceutical applications—where consistency, cleanability, and uptime are critical—taking a broader view of pump selection can lead to more reliable and efficient outcomes over the long term.

Centrifugal pumps are widely used in hygienic processing because of their ability to deliver smooth, continuous flow with relatively simple mechanical design. They perform particularly well when handling low-viscosity fluids such as water, cleaning solutions, and many finished liquid products. In these conditions, they can provide high flow rates with stable operation and relatively low maintenance requirements. However, their reliance on velocity to generate flow also makes them sensitive to changes in system conditions. As resistance in the system increases, the pump’s ability to deliver flow decreases, and efficiency can decline if the pump is forced to operate outside of its intended range.

For this reason, effective pump selection begins not with the pump curve alone, but with a clear understanding of the application. The properties of the product being handled play a central role. Fluids that behave like water will generally align well with centrifugal pump performance, but as viscosity increases—even moderately—the hydraulic efficiency of the pump begins to drop. In some cases, this can result in higher energy consumption, reduced flow, and increased mechanical stress on components. Similarly, products that are sensitive to shear or that contain entrained air can introduce additional challenges that are not always apparent during initial sizing calculations.

Another important consideration is how the system will actually operate over time. Many hygienic processes are not static. Flow rates may vary, temperatures can change, and product characteristics may shift between batches or during different stages of production. A pump that performs well at a single design point may struggle under these changing conditions if it has not been selected with sufficient flexibility in mind. This is where the concept of the Best Efficiency Point, or BEP, becomes especially important. Every centrifugal pump has a range where it operates most efficiently and with the least amount of mechanical stress. Consistently operating too far to the left or right of this point can lead to vibration, seal wear, and reduced equipment life. In hygienic applications, where unplanned downtime can disrupt production schedules and impact product quality, maintaining operation near this optimal range is a key objective.

System design also plays a significant role in how a centrifugal pump performs. The pump itself cannot overcome poor piping decisions or restrictive layouts. Suction conditions, in particular, deserve careful attention. Long suction runs, undersized piping, or excessive fittings can reduce the pressure available at the pump inlet, increasing the risk of cavitation and unstable operation. On the discharge side, excessive throttling used to control flow can push the pump away from its efficient operating range. These system-level influences are often the difference between a pump that performs reliably and one that requires frequent adjustment or maintenance.

In hygienic environments, pump selection must also account for how the equipment will be cleaned and maintained. Clean-in-place systems place specific demands on pump design, including the ability to fully drain, avoid product entrapment, and withstand repeated exposure to cleaning solutions and temperature cycles. Internal geometry, surface finish, and seal configuration all contribute to how effectively a pump can be cleaned. Designs that support thorough cleaning without disassembly can help reduce downtime and support more consistent sanitation practices, which is especially important in regulated industries such as dairy and pharmaceutical processing.

Seal design is another area that can significantly influence both performance and serviceability. In many cases, the ease with which a seal can be accessed, inspected, and replaced has a direct impact on maintenance efficiency. Pumps that allow for simplified seal service without extensive disassembly can reduce labor requirements and help return equipment to operation more quickly. Over time, these considerations can have a meaningful effect on total cost of ownership, even if they are not immediately apparent during the initial selection process.

 

While standard sanitary centrifugal pumps are well suited for many applications, it is also important to recognize where variations of centrifugal technology may be required to address specific process challenges. Not all hygienic systems behave the same, and certain conditions can push beyond the practical limits of a traditional centrifugal design.

For example, applications involving CIP return, tank unloading, or situations where the pump must handle air or intermittent flow often benefit from a self-priming centrifugal design. Liquid ring style pumps are commonly used in these cases because they are capable of evacuating air and maintaining flow even when the suction line is not fully flooded. In hygienic processing, this type of design is often used to improve reliability in return systems where foam, air, or inconsistent flow conditions are present.

 

Similarly, processes that involve entrained air or foam—such as fermentation, mixing, or certain cleaning operations—can create unstable flow conditions for standard centrifugal pumps. In these environments, selecting a pump designed to better tolerate air handling can help maintain consistent performance and reduce the risk of flow disruption or loss of prime.

At the other end of the performance spectrum, some hygienic applications require significantly higher pressures than a standard centrifugal pump can efficiently provide. Membrane filtration systems, including reverse osmosis and ultrafiltration, are common examples. These processes demand consistent, high-pressure flow without pulsation, often over extended operating periods. Multi-stage centrifugal pumps are typically used in these situations, as they are designed to generate higher pressures by using multiple impellers in series while maintaining smooth, continuous flow characteristics.

 

Recognizing when these alternative centrifugal designs are more appropriate is an important part of the selection process. Rather than trying to force a standard pump to operate outside of its ideal range, matching the pump design to the application can lead to more stable operation, improved efficiency, and longer equipment life.

One of the more common challenges in centrifugal pump selection is the tendency to oversize. This is often done as a precaution, with the assumption that additional capacity provides a margin of safety. In reality, oversizing frequently leads to throttled operation, where flow is artificially restricted to meet process requirements. This not only wastes energy but also forces the pump to operate away from its Best Efficiency Point, increasing wear on internal components. A more effective approach is to size the pump as closely as possible to actual operating conditions, while accounting for reasonable variability in the process.

Ultimately, selecting a sanitary centrifugal pump is not about choosing a standalone piece of equipment, but about understanding how that equipment will function within a broader process system. The interaction between the pump, the piping, the product, and the operating conditions determines the overall performance. Taking the time to evaluate these relationships during the selection phase can help avoid many of the issues that lead to inefficiency, maintenance challenges, or inconsistent operation.

Sanitary centrifugal pumps remain a highly effective solution for many hygienic applications, particularly those involving low-viscosity fluids and steady flow requirements. When selected with a full understanding of the application and system dynamics, they can provide reliable, efficient performance over long operating periods. For processors looking to optimize their systems, a thoughtful and application-driven approach to pump selection is one of the most valuable steps they can take.

For additional guidance on selecting the right sanitary centrifugal pump for your application—including applications involving self-priming requirements, air handling, or high-pressure systems—consider connecting with your local authorized Fristam distributor or a Fristam application expert to review your system requirements in more detail.

In pharmaceutical manufacturing, few utilities are as critical—or as tightly controlled—as Water for Injection (WFI). Used in applications ranging from formulation and dilution to final rinsing and sterilization processes, WFI must consistently meet stringent standards for purity and microbiological control. While much of the focus is often placed on how WFI is generated and stored, the equipment used to move it throughout a system plays an equally important role. Pumps in WFI service are not simply selected for flow and pressure—they must be designed to protect the integrity of the entire system.

What makes WFI applications unique is the expectation that every component in contact with the fluid supports hygienic design principles at the highest level. Unlike typical process fluids, WFI systems operate under conditions where even minor areas of stagnation or surface irregularities can introduce risk. These systems are often maintained at elevated temperatures or routinely subjected to hot water or steam sanitization, and many operate continuously to prevent microbial growth. As a result, pumps used in WFI service must be engineered with cleanability, drainability, and repeatable performance in mind, while also supporting system validation and regulatory compliance.

One of the most distinctive features of WFI pump installations is the inclusion of flush piping, often paired with diaphragm valves. This design approach is intentional and serves a critical function. The flush system ensures that sensitive areas of the pump—particularly around the mechanical seal—are continuously or periodically exposed to clean WFI. By doing so, it helps eliminate low-flow zones where fluid could otherwise stagnate, reduces the risk of microbial growth, and allows high-temperature water or steam to reach areas that would be difficult to clean through standard flow paths alone. The use of diaphragm valves further supports this objective by providing a hygienic, crevice-free means of controlling flow, ensuring that the flush system itself does not introduce new contamination risks. Together, these elements help maintain the cleanliness and integrity of the pump within the broader WFI loop.

Surface finish is another critical consideration that extends beyond a simple specification on a datasheet. In WFI systems, internal surface roughness is tightly controlled because it directly impacts cleanability and microbial resistance. Smoother surfaces reduce the likelihood of bacteria adhering to the material and improve the effectiveness of cleaning and sterilization cycles. Electropolishing is often used to further refine the surface, enhancing corrosion resistance and supporting the formation of a stable passive layer. These characteristics are essential not only for maintaining system hygiene, but also for ensuring consistent, repeatable performance during validation and operation.

Material selection follows similar principles. Pumps used in WFI applications are typically constructed from high-quality stainless steel, such as 316L, with careful attention paid to metallurgy and fabrication practices. The goal is to create a fully drainable, crevice-free flow path that minimizes the potential for contamination while maintaining long-term durability. However, physical design alone is not sufficient in pharmaceutical environments. Documentation and traceability are equally important, as they provide the evidence required to support system qualification and ongoing compliance.

For this reason, WFI pumps are often supplied with comprehensive documentation packages that include material certifications, surface finish reports, and records related to fabrication and finishing processes. These documents play a key role during installation and validation activities, as well as during regulatory audits. They help ensure that every wetted component can be traced, verified, and trusted to perform as intended within a highly controlled environment.

WFI pumps are commonly used in distribution loops, storage tank recirculation, CIP and SIP systems, and final rinse applications, as well as in processes involving high-purity fluids such as buffers or injectable solutions. Across these applications, the expectations remain consistent: maintain fluid purity, support hygienic operation, and deliver reliable performance under demanding conditions.

Ultimately, selecting a pump for WFI service requires a broader perspective than typical hygienic applications. It is not only about meeting flow requirements, but about ensuring that every aspect of the pump—from seal design and flush systems to surface finish and documentation—supports the overall integrity of the process. Attention to these details can help prevent operational challenges, simplify validation, and contribute to long-term system reliability.

For processors evaluating WFI pump requirements or looking to optimize existing systems, working with experienced partners can provide valuable insight. Contact your local authorized Fristam distributor or connect with a Fristam application expert to discuss your specific application and explore solutions designed to support high-purity processing environments.

Selecting the right pump technology is one of the most important decisions in hygienic process design. While both centrifugal and positive displacement pumps are widely used, they operate on fundamentally different principles—and choosing the wrong type can lead to inefficiencies, product damage, or unnecessary operational challenges.

Understanding how each technology behaves under real operating conditions – not just in theory, can help processors make more confident, informed decisions.

Centrifugal pumps are typically the preferred choice for low-viscosity fluids, especially those similar to water (generally below ~100–200 cP). Their design enables smooth, continuous flow with relatively simple construction and low maintenance requirements. In hygienic systems, they are commonly used for transferring water, CIP solutions, and other low-viscosity liquids where high flow rates are required.

However, centrifugal pumps rely on velocity to generate flow, which makes them sensitive to changes in system conditions. As system resistance increases, flow rates decrease. This means that in systems with variable backpressure—such as long piping runs, filtration systems, or heat exchangers—flow can become inconsistent. Maintaining performance often requires careful system design or the use of variable frequency drives (VFDs).

Positive displacement pumps operate differently, moving a fixed volume of product with each rotation. This makes them better suited for higher-viscosity fluids (often above ~500 cP and well into the thousands or up to a million cP or more) or applications where consistent flow is required regardless of system pressure. Products such as yogurt, sauces, creams, or concentrates benefit from the steady, predictable flow these pumps provide.

They are also a strong choice for shear-sensitive products, where maintaining texture, particle integrity, or emulsion stability is important. Because positive displacement pumps operate at lower speeds and do not rely on high velocity, they can reduce the risk of product degradation.

That said, these advantages come with tradeoffs. Positive displacement pumps require proper system protection, such as pressure relief valves, because they will continue to generate flow even if downstream restrictions increase. They may also involve more complex maintenance compared to centrifugal designs, depending on the application and pump type.

In many hygienic systems, the decision is not purely based on viscosity—it also depends on how the process operates. For example, applications involving entrained air, foaming, or intermittent flow (such as tank emptying or CIP return) can challenge traditional centrifugal pumps. In these cases, selecting a pump that can handle varying inlet conditions becomes just as important as viscosity considerations.

This is where newer technologies, such as twin screw pumps, have introduced a hybrid approach. These pumps can handle a wide range of viscosities while also operating at higher speeds for CIP, allowing them to function as both a process pump and a cleaning pump. In systems where reducing equipment count or simplifying piping is a priority, this flexibility can offer meaningful advantages.

Ultimately, the choice between centrifugal and positive displacement pumps comes down to a combination of factors:

• Viscosity of the product
• Required flow consistency
• System pressure variability
• Sensitivity of the product to shear
• Presence of air or vapor in the process
• Cleaning requirements and system design

In simpler terms:

• If the application involves low-viscosity, high-flow transfer with stable conditions, a centrifugal pump is often the most efficient solution.
• If the process requires consistent flow, handles higher viscosities, or needs gentle product handling, a positive displacement pump is typically the better choice.
• If the system must handle multiple duties (process + CIP) or variable conditions, a hybrid approach like a twin screw pump may be worth considering.

Taking the time to evaluate these factors early in the design process can help avoid common performance issues and reduce the need for future system modifications. Have additional questions on which pump type is right for you? Contact you local authorized Fristam distributor or one of our application experts for additional information.

In pump system design, few concepts are as important—and as frequently misunderstood—as Net Positive Suction Head (NPSH). While often treated as a specification detail buried in pump curves, NPSH plays a major role in determining whether a pump will operate reliably or encounter performance problems such as cavitation, noise, vibration, or premature wear. For processors handling valuable products, understanding NPSH can help prevent operational disruptions and support more stable, efficient pump performance.

Net Positive Suction Head refers to the amount of pressure available at the pump inlet to keep the fluid in a liquid state as it enters the pump. This available pressure, commonly called NPSHa (Net Positive Suction Head Available), must exceed the amount of pressure the pump requires to operate properly, known as NPSHr (Net Positive Suction Head Required). When available suction pressure falls too close to—or below—the pump’s required NPSH, vapor bubbles can form and collapse inside the pump. This phenomenon, known as cavitation, can reduce performance and contribute to component damage over time.

NPSHa > NPSHr

A common misconception is that NPSH is only a concern in high-temperature or extreme operating conditions. In reality, NPSH limitations can arise in many hygienic processing applications, including viscous product transfer, tank unloading, long suction runs, or systems handling elevated temperatures. Even relatively small design decisions—such as undersized suction piping, restrictive fittings, or excessive lift—can reduce available suction head and create operating challenges.

Another common misconception is that NPSHa is determined solely by the height of liquid above the pump inlet. In reality, NPSH is based on absolute pressure, not gauge pressure. The reference point begins at a perfect vacuum (0 feet absolute). At sea level, an open tank provides approximately 34 feet of absolute pressure from the atmosphere alone. At higher elevations—such as Denver (around 5,300 feet)—this drops to roughly 28 feet.

From this baseline, NPSHa is calculated by adding the static liquid height above the pump, then subtracting friction losses in the suction piping and the fluid’s vapor pressure. The result is the true pressure available at the pump inlet to keep the fluid in a stable liquid state.

Temperature is one factor that can significantly affect NPSH. As fluid temperature rises, vapor pressure increases, which reduces the margin between suction pressure and vaporization. Product viscosity can also influence suction conditions, particularly when thicker fluids create additional friction losses in the inlet line. Entrained air, common in certain food, dairy, or personal care processes, can further complicate suction stability and contribute to inconsistent performance. Entrained air is governed by different physics than cavitation, but it can disrupt product flow just as much—if not more—in certain applications.

Many NPSH-related problems are not immediately recognized as suction issues. Operators may observe noise, reduced flow, erratic performance, or premature seal and component wear without identifying inadequate suction conditions as the root cause. This is one reason NPSH deserves consideration during system design—not simply after problems occur.

Improving NPSHa often begins with evaluating the system, not just the pump. Shortening suction lines, increasing pipe diameters, reducing restrictions, improving tank geometry, or lowering fluid temperatures can all help improve suction conditions. In some cases, however, the better solution may involve reevaluating pump selection to ensure the equipment is well matched to the application.

Understanding the relationship between NPSHa and NPSHr helps move pump selection beyond flow and pressure alone. It supports a more complete view of system performance and can help reduce risk in demanding hygienic applications. For processors seeking reliable performance, NPSH is not simply a technical formula on a curve—it is a practical design consideration that can influence long-term uptime, product quality, and operating efficiency.

If you are evaluating a challenging application or experiencing inconsistent pump performance, consulting a pump application specialist can help identify whether suction conditions may be contributing to the issue.