How Pump Choice Dictates Product Quality

Choosing the right tool for the job can save time and money down the line.

Ken Ruckreigel | Rodem Inc.

| IMAGE 1: This illustration is an example of how high volumetric efficiency, designed by a reduced slip through close clearances, means optimal pump selection, ensures reliable operation, product quality and yield. (Images courtesy of Rodem)

During the design phase of any hygienic processing operation, it is critical to consider the product-handling requirements of each fluid and suspended solid that may pass through each pump. Overlooking high-value inclusions like diced fruits, vegetables, proteins, curd particles and more can result in product degradation and quality issues and can directly impact the producer’s yield-on-investment.

The key to successfully balancing sensitive product handling with throughput is an engineering and design shift from a “volume-first” mindset to an “integrity-first” philosophy. Engineers who prioritize proper design considerations and successful implementation will pay dividends in the long term through efficiency, product integrity and minimal waste.

Environmental Impacts: A Plus to Positive Product Integrity

A properly selected pump actively prevents food loss and waste during production, supporting environmentally conscious processors’ sustainability initiatives and environmental, social and governance (ESG) targets.

Particle Destruction Mechanics

There are several mechanical concepts that can negatively impact product integrity during the pumping process. In their most basic form, these concepts can be explained as squeezing, rubbing and smashing. It is best to examine each concept in simple terms to understand why there is no standard when it comes to process pumps.

What Is Shear & Why Does It Matter?

Shear is defined as the relative motion or sliding between adjacent layers of moving fluid caused by external mechanical force. Simply put, shear happens when one layer of fluid moves faster than the neighboring layer.

During the pumping process, the fluid touching the active rotor is moving quickly, while the liquid along the casing wall is stationary. The tiny gap between the two is where the shear happens.

Although small in size, this gap where shear takes place can take on a significant role in product integrity if it is smaller than the size of the solid or particle moving through the pump casing. In this case, the result is product damage by the pump instead of a steady and efficient flow.

| IMAGE 2: In centrifugal pumps, high-velocity impellers act as blenders and wreak havoc on delicate solids and particles. The impeller-generated flow is naturally turbulent, and impeller tips are prone to shear, making it destructive for sensitive products.

Mechanical Clearance’s Impact on Integrity

Precisely designed mechanical clearance in hygienic pumps is the tight working space between the parts in motion, like the rotor or impeller, and the stationary pump casing. While large gaps might be permissible in industrial applications, hygienic processes require exact tolerances to ensure proper cleaning, maximum efficiency and, for the purpose of this discussion, guaranteed product integrity and quality.

Proper clearances ensure the gentle handling of shear-sensitive products without breakdown or damage. The result is an end product with the exact texture and structure as intended by the manufacturer.

Flow: Laminar vs. Turbulent

Velocity contributes to the rate of flow. Flow is a critical consideration for food and beverage products containing particulates. In hygienic pumps, engineers categorize flow in two ways:

Laminar flow is smooth and occurs at lower velocities. Because of its predictable characteristics, it is ideal for transporting sensitive products and for gentle product handling.
Turbulent flow occurs at higher velocities and is necessary for clean-in-place (CIP) processes. Because turbulent flow creates chaos, it is used for product mixing but is not suitable for moving delicate products.

When the flow transitions from laminar to turbulent, it is categorized as critical velocity. This is predicted by determining the Reynolds number, factoring both inertial and viscous forces. Knowing this threshold is key to protecting delicate solids during processing.

Product Viscosity & Flow

The textbook definition of viscosity is “a fundamental fluid property measuring internal resistance to flow or deformation,” but it is often talked about in terms of a product’s thickness or stickiness. Product viscosity plays an important role in flow. Laminar flow occurs at lower speeds or with high-viscosity liquids, while turbulent flow occurs at high speeds or with low-viscosity fluids. Factoring viscosity into the equation is a must for precise product handling and proper pump operation.

| IMAGE 3: Pumps are a necessity for moving fluids in every processing plant. The right pump for the task and an integrity-first mindset are the competitive advantages processors must jump on in a world full of tight budgets, timelines and demanding production schedules.

Finding the Right Pump for the Product

Having gained a better understanding of some of the most important physics principles and considerations when targeting gentle transfer, it is time to match the various pumping technologies with the textures they best serve.

Centrifugal pumps

Centrifugal pumps are a common and cost-efficient option for fluid transfer in hygienic processes and are often called the “workhorses” of the plant. However, they are often not the right pump for gentle product handling or solids.

Centrifugal pumps use a high-speed impeller to force fluid toward the outside of the casing through centrifugal force. These high-velocity impellers act as blenders and wreak havoc on delicate solids and particles. The impeller-generated flow is naturally turbulent, and impeller tips are prone to shear, making it destructive for fragile solids.

Positive displacement

Positive displacement pumps trap fluids and transfer a fixed volume per cycle, making them a good fit for shear-sensitive liquids and fluids containing solids.

It is important to remember that positive displacement pumps are a general term for an entire family of pumps, so it is not a cut-and-dried solution. The most common positive displacement pumps among food, beverage and other hygienic processors are the rotary lobe, circumferential piston, twin-screw and diaphragm pumps.

Rotary lobe and circumferential piston pumps: These are the most common positive displacement pumps in food processing and are ideal for maintaining product integrity and protecting the bottom line. They move product in pockets with two rotators moving in opposite directions. While the clearances have tight tolerances for consistent flow, there is one key area for danger if not accounted for. Processors must ensure that backpressure is not too great and that the product is not too thin and thus is able to slip through the clearances (called “slip”), which can cause degradation. Also important is precise speed control for fragile solids.
Twin-screw pumps: These pumps move fluid in a straight line with two intermeshing screws. They are ideal for large inclusions because of the large pockets where fluid moves between screws without the risk of pinching and destruction. Not only are they generally an ideal option for necessary gentle fluid handling, but they also offer unmatched flexibility. Twin-screw pumps can go from steady, consistent flow to turbulent flow for CIP. The upfront cost of twin-screw pumps can be higher, but the cost often balances out since it is possible to use one pump for both cleaning and processing.
Diaphragm pumps: Diaphragm pumps use air and two flexible diaphragms to direct flow. Because this technology pushes product without the use of rotating mechanics or tight clearances and utilizes flap valves for large inclusions, it is a good option for handling a variety of media, including solids, viscous products and slurries.

Other positive displacement pumps fit for delicate transfer utilize a single rotor design to suction solids and avoid pinch points or move fluid by squeezing a flexible hose or tube with rotating rollers.

Impact on the Bottom Line

With various properties at play and pump technology options for handling high-value products with sensitive makeup and particles, processors must fully examine the requirements and balance both product integrity and profit.

Energy vs. integrity: A pump touted as high-efficiency, when used in the wrong context and resulting in product destruction, is a greater liability and expense than a pump less praised for mechanical efficiency if it protects 100% of the product.
Maintenance and downtime: The right pump for the product texture and application results in reduced maintenance and downtime. Another key consideration is the ability to use the twin-screw pump for both CIP and process, eliminating the need for two pumps and two sets of spare parts.
The recall factor: Quality not only refers to product consistency, but also safety and brand reputation. Equipment designed for its intended application will help prevent product inconsistency and contamination.

Ken Ruckriegel joined Rodem as an account manager in 2024 as part of the North Carolina team. He was later promoted to southeast regional sales manager. For more information, visit rodem.com.

In This Issue

Cover Series Chemical Processing