What Causes Shear in Hygienic Pumps — and How to Protect Sensitive Products

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.