Temperature is an important consideration in hygienic pumping applications because it can change both product characteristics and operating conditions.

In food, beverage, dairy, pharmaceutical, and personal care processing, a pump may handle product at one temperature and significantly hotter fluids during Clean-in-Place (CIP). These temperature changes can influence viscosity, suction conditions, internal clearances, seals, and elastomers.

Understanding these effects helps ensure the pump is properly selected for the full range of process conditions.

Temperature Changes Viscosity

For many products, viscosity decreases as temperature increases. A syrup, oil, concentrate, cream, or other viscous product may therefore behave very differently at 40°F than it does at 140°F.

Viscosity can affect friction loss through the piping system, pump efficiency, required torque and horsepower, and the type of pump best suited for the application.

For this reason, pump selection should consider the product’s viscosity at its actual pumping temperature. When a process experiences a wide temperature range, viscosity should be evaluated at the relevant minimum and maximum operating temperatures.

Higher Temperatures Can Affect NPSH

Temperature can also have a significant effect on the suction conditions of a centrifugal pump.

As liquid temperature increases, its vapor pressure increases. This reduces the margin between Net Positive Suction Head Available (NPSHa) from the system and Net Positive Suction Head Required (NPSHr) by the pump.

If sufficient NPSH is not available, the liquid can begin to vaporize as it enters the pump, potentially resulting in cavitation and reduced pump performance.

Applications involving hot products or elevated-temperature fluids should therefore account for liquid temperature along with tank level, pump placement, suction piping, pipe diameter, and restrictions when evaluating NPSH.

Temperature Can Affect Internal Clearances

Temperature changes can also affect the internal clearances of positive displacement pumps as components expand and contract. This is particularly important when there is a significant temperature difference between production and CIP.

Applications with large temperature swings may require clearances specifically selected for those conditions. For a more detailed explanation, see our article on Hot Clearance Rotors and Temperature Differentials.

Consider Seals and Elastomers

Mechanical seals, O-rings, and other elastomers must be compatible with the complete process, not just the product being pumped.

During cleaning, these components may be exposed to elevated temperatures as well as caustic solutions, acids, sanitizers, and other chemicals. The combination of temperature, chemical concentration, and exposure time can influence material performance and service life.

Seal and elastomer selection should therefore consider both production and cleaning conditions.

Don’t Overlook CIP Conditions

Normal production conditions are only part of the application. During CIP, the pump may encounter different temperatures, viscosities, flow rates, pressures, and suction conditions than it experiences while pumping product.

For example, a pump selected to move a viscous product at a relatively low speed may also be expected to move low-viscosity cleaning solution at a much higher flow rate. Those two operating points can place very different demands on the pump and system.

Evaluating both production and CIP conditions helps ensure the pump can perform effectively throughout the complete process cycle.

Look at the Complete Operating Range

Temperature should not be considered as an isolated value on an application data sheet. Its effects can extend throughout the pumping system by changing product viscosity, vapor pressure, suction conditions, component clearances, and material requirements.

When evaluating a hygienic pump application, consider the minimum and maximum product temperatures, viscosity at those temperatures, CIP temperature and flow requirements, suction conditions, required flow and pressure, and cleaning chemistry.

Understanding the complete operating range helps ensure the pump is properly configured for reliable performance during both production and cleaning.

For applications involving significant temperature changes, hot products, or demanding CIP conditions, Fristam application engineers and authorized distributors can help evaluate your process and determine the appropriate hygienic pump configuration.

Pipe size can have a significant impact on the performance of a hygienic processing system. For a given flow rate, pipe diameter determines fluid velocity, which influences friction loss, pressure requirements and the amount of energy required to move product through the process.

A pipe that is too small can create excessive velocity and pressure loss. However, simply increasing pipe diameter is not always the answer. Larger piping costs more, increases product hold-up and may not provide the desired velocities for certain process or cleaning conditions.

Proper pipe sizing requires balancing flow, velocity, pressure loss and the requirements of the product and process.

How Pipe Diameter Affects Fluid Velocity

For a fixed flow rate, reducing pipe diameter forces the same volume of fluid through a smaller cross-sectional area. The result is higher fluid velocity. Increasing pipe diameter has the opposite effect.

This relationship is important because even a relatively small change in pipe diameter can create a significant change in velocity.

For example, moving the same flow through a smaller line requires the product to travel faster. That higher velocity affects how much resistance the fluid encounters as it moves through the system.

Higher Velocity Means Greater Friction Loss

As fluid travels through piping, energy is lost to friction. Resistance occurs along the pipe wall and as the fluid passes through elbows, valves, tees, reducers, heat exchangers, filters and other process components.

As velocity increases, these friction losses can rise significantly.

This means an undersized pipe can require the pump to generate considerably more pressure to maintain the desired flow. Increasing pipe diameter generally reduces velocity and friction loss, allowing the same volume of product to move through the system with less resistance.

Pipe length also matters. Every foot of pipe contributes friction loss, so the effect of pipe diameter becomes increasingly important as piping runs become longer or contain numerous fittings and process components.

Pipe Size Can Affect Energy Requirements

Pressure lost to friction represents energy that must be supplied by the pump.

If an unnecessarily small pipe creates excessive system resistance, additional pumping energy is required to achieve the desired flow. Over the operating life of a process system, this can make pipe sizing an energy and operating-cost consideration as well as an engineering decision.

Larger piping can reduce these losses, but bigger is not automatically better. Larger tubing, valves and fittings increase installed cost and the amount of product contained within the piping.

The objective is to select a pipe diameter that provides acceptable velocity and pressure loss without unnecessarily increasing the size of the system.

Product Characteristics Matter

Pipe sizing should not be based on flow rate alone. The characteristics of the fluid being transferred also affect how easily it moves through the system.

Water, cleaning solutions and other low-viscosity fluids generally move through piping with relatively low resistance. More viscous products such as creams, syrups, sauces and concentrates can create substantially greater pressure losses.

Temperature can also change the viscosity of many products. A product that flows readily when warm may behave very differently at a lower temperature.

For this reason, piping calculations should reflect the actual product properties and operating temperatures expected in the process rather than relying exclusively on conditions based on water.

Pay Particular Attention to Suction Piping

Pipe sizing is especially important on the suction side of a pump because friction loss in the suction line reduces the pressure available at the pump inlet.

A suction line that is too small, excessively long or contains unnecessary restrictions can create unfavorable inlet conditions before the fluid reaches the pump. Elbows, valves, strainers and other components add additional losses, particularly at higher fluid velocities.

Good system design therefore considers not only how easily the pump can move product through the discharge piping, but also how effectively product can reach the pump.

Production and CIP May Require Different Conditions

Hygienic processing adds another consideration because the same piping frequently handles both product and cleaning solutions.

During production, a line may carry a viscous product at one flow rate and temperature. During Clean-in-Place (CIP), the same line may carry a low-viscosity cleaning solution at a considerably different flow rate.

Pipe diameter must accommodate both operating conditions. A line sized only around production requirements may not provide the desired conditions during cleaning, while a system designed solely around CIP may not be optimal for product transfer.

Evaluating both duties helps ensure the piping supports the complete operating cycle.

Finding the Right Pipe Size

Proper pipe sizing is ultimately about balance. The pipe must accommodate the required flow without creating excessive velocity and friction loss, while also accounting for product characteristics, suction conditions, cleaning requirements and system configuration.

Even relatively small changes in pipe diameter can have a meaningful effect on system resistance. Understanding that relationship can help process engineers make better decisions when designing a new system, increasing production capacity or modifying an existing process.

Fristam’s Friction Loss Calculator can help evaluate these conditions using actual flow rate, viscosity, specific gravity, temperature, tubing size and length, along with valves, elbows, tees and other system losses.

Understanding the relationship between pipe diameter, velocity and friction loss helps ensure the pump and piping are evaluated as parts of the same system. Fristam application engineers and authorized distributors can also assist in evaluating process conditions and selecting the appropriate pumping solution.

Moving peanut butter, concentrates, syrups, pastes, creams and other high-viscosity products requires more from a pump than simply achieving the required flow rate and pressure.

As viscosity increases, so does the torque typically required to move the product. Depending on differential pressure, temperature, pump speed and system conditions, those forces may be sustained for thousands of operating hours.

That changes the question processors should ask when evaluating a positive displacement pump.

It isn’t simply: Can the pump move the product?

A better question is: How is the pump designed to handle the mechanical forces created while moving that product over time?

For demanding high-viscosity applications, several design and application factors deserve a closer look.

Start with the Shaft and Rotor Design

Pump shafts transmit torque from the drive system to the pumping elements. As torque increases, shaft strength and rigidity become increasingly important.

A robust shaft helps resist twisting and deflection under load. Even relatively small amounts of deflection can become important in a positive displacement pump because the rotating components operate with carefully controlled internal clearances.

When evaluating a pump, consider more than shaft diameter alone. Shaft material, unsupported shaft length, bearing support and the overall drivetrain design all influence how well the rotating assembly maintains its position under load.

Rotor design also plays an important role. As rotors move a viscous product through the pump, forces are generated across the pumping elements. A balanced rotor design can help manage these forces, reduce shaft deflection and maintain proper rotor positioning.

The objective is simple: keep the rotating assembly where it was designed to operate, even when the pump is working hard.

Understand Why Internal Clearances Matter

Positive displacement pumps rely on carefully engineered clearances between rotating and stationary components. These clearances help provide efficient product movement while preventing unwanted contact between components.

Under sustained loading, however, shaft or rotor deflection can alter those relationships. If components move outside their intended operating positions, the potential for contact and accelerated wear can increase.

This is why internal clearances shouldn’t be evaluated as an isolated specification. Look at how the pump’s shafts, rotors, bearings and gearbox work together to maintain those clearances during actual operation.

For high-viscosity service, maintaining alignment under load can be just as important as the clearance itself.

Don’t Overlook the Gearbox

The gearbox does not touch the product, but it has a major influence on what happens inside the pumping chamber.

Bearings support the shafts and control radial and axial movement, while the gearbox provides the structural foundation for the shafts, bearings and timing gears. Under sustained torque, rigidity throughout this assembly helps maintain alignment.

When comparing positive displacement pumps, examine the complete drivetrain rather than focusing only on published flow, pressure or torque ratings.

Consider:

• Shaft size and support
• Rotor design and balance
• Bearing arrangement
• Timing gear design
• Gearbox construction
• Internal clearances

These components function as a system. A high torque rating has limited meaning if the mechanical design cannot maintain proper alignment while transmitting that torque continuously.

Consider the Worst Operating Condition—Not Just Normal Production

One of the easiest mistakes when sizing a pump for a viscous product is evaluating only normal operating conditions.

Viscosity can change dramatically with temperature.

A product that flows reasonably well during production may become considerably thicker after cooling in a process line overnight or between batches. As a result, the pump may experience some of its highest torque requirements during startup rather than during normal steady-state operation.

Cleaning temperatures matter as well. Pump components expand as temperatures increase, so internal clearances must accommodate the complete range of product and cleaning temperatures the pump will experience.

When evaluating an application, consider the worst expected combination of viscosity, temperature and differential pressure, not simply the conditions during normal production.

Make Sure the Product Can Reach the Pump

Heavy-duty construction cannot compensate for poor pump sizing or inadequate inlet conditions.

Highly viscous products can be particularly challenging on the suction side because they don’t flow readily through piping and into the pumping chamber.

Simply increasing pump speed is rarely the answer. If the product cannot enter the pumping cavities quickly enough, increasing speed can result in incomplete cavity filling and reduced pump performance.

For very viscous products, proper inlet piping, adequate suction conditions and an appropriate operating speed can be every bit as important as the pump’s mechanical design.

This is why successful high-viscosity applications require looking at the entire process system, not just the pump.

Look Beyond the Published Flow Rate

Two positive displacement pumps may have similar published flow and pressure capabilities yet behave very differently when subjected to sustained high-viscosity service.

Look deeper than the basic specifications.

How are the shafts supported? How does the rotor design manage load? How are internal clearances maintained? How robust are the bearings, timing gears and gearbox? And how will the pump perform when the product is at its coldest, thickest or most difficult operating condition?

These are the questions that can separate a pump that simply meets the published duty point from one designed for long-term operation in demanding service.

The Fristam FKL positive displacement pump was engineered with these conditions in mind. Large-diameter shafts, balanced rotors, close internal clearances and heavy-duty split-style gearbox construction work together to provide the rigidity and mechanical support needed for demanding hygienic processing applications.

Selecting the right pump, however, still depends on the application.

To determine the appropriate positive displacement pump for your process, contact a Fristam application expert or your local authorized Fristam distributor. Our team can evaluate product characteristics, viscosity, flow requirements, differential pressure, temperature, piping and operating conditions to properly select and size the pump for your process.

In hygienic processing applications, equipment reliability is essential. Whether producing dairy products, beverages, pharmaceuticals, cosmetics, or prepared foods, unexpected downtime can disrupt production schedules, increase maintenance costs, and impact product quality.

Maximizing pump reliability involves much more than selecting a high-quality pump. The overall performance and service life of any hygienic pumping system are influenced by proper equipment selection, operating conditions, installation practices, cleaning procedures, and routine maintenance.

By considering the entire process and not just the pump itself—manufacturers can improve equipment reliability, reduce maintenance requirements, and maximize their return on investment.

Select the Right Pump for the Application

Reliable operation begins with selecting the appropriate pump technology.

Centrifugal pumps excel in applications involving low-viscosity products and higher flow rates, while positive displacement pumps are often better suited for viscous products, products containing particulates, or applications requiring consistent flow regardless of pressure.

Understanding product characteristics such as viscosity, solids content, shear sensitivity, temperature, and desired flow rate helps ensure the selected pump operates within its intended design parameters. Proper pump selection not only improves performance but also reduces unnecessary stress on components throughout the life of the equipment.

Operate Within the Recommended Performance Range

Every pump is designed to operate most efficiently within a specific portion of its performance curve. For centrifugal pumps, this area is commonly referred to as the Best Efficiency Point (BEP).

Operating significantly above or below this range for extended periods can increase hydraulic loads, vibration, shaft deflection, and wear on bearings and mechanical seals. Reviewing pump curves during equipment selection and verifying operating conditions during commissioning helps ensure the pump delivers both efficient performance and long-term reliability.

Provide Proper Suction Conditions

A pump can only perform as well as the product supplied to its inlet.

Restrictive suction piping, inadequate Net Positive Suction Head (NPSH), or unnecessary pressure losses can reduce performance and increase the risk of cavitation. Cavitation occurs when vapor bubbles form within the pump and collapse as pressure increases, potentially leading to vibration, noise, and damage to internal components over time.

Designing suction piping to minimize restrictions and ensuring adequate product supply allows the pump to operate smoothly and efficiently.

Protect Mechanical Seals

Mechanical seals are among the hardest-working components within a hygienic pump. They rely on the process fluid to lubricate and cool the seal faces during operation.

Conditions such as dry running, improper seal selection, or incompatibility with cleaning chemicals can significantly reduce seal life. Selecting seal materials appropriate for both the product being processed and the facility’s cleaning procedures helps maximize reliability while minimizing unplanned maintenance.

Consider the Entire Process—Not Just Normal Operating Conditions

Many applications experience changes throughout production. Product temperature may increase, viscosity may change, air may become entrained, or cleaning cycles may expose equipment to elevated temperatures and aggressive chemicals.

Evaluating how these varying conditions affect pump performance ensures the selected equipment can operate reliably throughout every stage of production—not simply during normal operation.

Follow Recommended Cleaning and Maintenance Practices

Clean-in-place (CIP) systems are essential in hygienic processing, but proper cleaning procedures are equally important for long-term equipment performance.

Following recommended cleaning temperatures, chemical compatibility guidelines, and maintenance schedules helps preserve elastomers, mechanical seals, and other wear components. Routine inspections for vibration, alignment, bearing condition, and pipe strain can often identify small issues before they become larger maintenance concerns.

Partner with Experienced Application Specialists

Every hygienic process presents unique challenges. Products evolve, production requirements change, and new applications often introduce variables that were not considered during the original system design.

Working with experienced application engineers during equipment selection—or when modifying an existing process—can help identify opportunities to improve reliability, increase efficiency, and reduce long-term operating costs.

Reliable Performance Begins with the Right Approach

High-quality hygienic pumps are designed to provide dependable performance for many years when properly applied and maintained. By taking a system-wide approach to equipment selection, operation, and maintenance, processors can maximize equipment life while minimizing downtime and maintenance costs.

Need Help Optimizing Your Hygienic Pumping System?

Whether you’re designing a new process or looking to improve the performance of an existing one, Fristam’s experienced application engineers can help evaluate your requirements and recommend the best hygienic pumping solution for your application.
To connect with your local Fristam authorized distributor or speak directly with a Fristam application expert, visit our Contact / Where to Buy page.

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.