Pumps for Viscous Liquids

  • Post last modified:January 16, 2026

Mastering Fluid Handling: The Ultimate Guide to Pumps for Viscous Liquids

In the world of industrial fluid management, not all liquids are created equal. While moving water or thin solvents is a relatively straightforward engineering task, handling thick, sticky, or semi-solid substances presents a unique set of challenges. Whether you are dealing with molasses in a food processing plant, crude oil in a refinery, or polymer resins in a chemical facility, selecting the right pumps for viscous liquids is critical to operational efficiency, equipment longevity, and product integrity.

Viscosity is the measure of a fluid’s resistance to flow. As viscosity increases, the internal friction of the liquid rises, requiring more energy to move it through pipes and valves. Standard centrifugal pumps, which are the workhorses of the water industry, often fail or become highly inefficient when tasked with high-viscosity media. This guide explores the science of viscosity, the various pump technologies designed to handle thick fluids, and how to choose the right system for your specific application.

Understanding Viscosity and Its Impact on Pumping

Before diving into pump hardware, it is essential to understand the physics of the fluids being moved. Viscosity is typically measured in Centipoise (cP). For reference, water has a viscosity of 1 cP, motor oil is around 100-500 cP, and honey sits at approximately 10,000 cP. Some industrial pastes can exceed 1,000,000 cP.

Newtonian vs. Non-Newtonian Fluids

Fluids behave differently under stress. Understanding these behaviors is the first step in selecting pumps for viscous liquids:

  • Newtonian Fluids: These maintain a constant viscosity regardless of the shear rate (the speed of agitation). Examples include water, mineral oils, and alcohol.
  • Thixotropic (Shear-Thinning) Fluids: These become less viscous as they are stirred or pumped. Ketchup and many paints are classic examples.
  • Dilatant (Shear-Thickening) Fluids: These become more viscous when stress is applied. Quickstand or cornstarch in water are examples. These are particularly difficult to pump because the faster the pump runs, the “harder” the fluid becomes.

The “Centrifugal Problem”

Centrifugal pumps rely on high-speed impellers to impart kinetic energy to the fluid. When a centrifugal pump encounters a viscous liquid, the friction losses within the pump casing increase exponentially. The flow rate drops, the head pressure decreases, and the power consumption spikes. Generally, once a fluid exceeds 500 to 1,000 cP, centrifugal pumps become uneconomical and prone to mechanical failure.

Top Technologies: The Best Pumps for Viscous Liquids

When viscosity rises, engineers turn to Positive Displacement (PD) pumps. Unlike centrifugal pumps, PD pumps move a fixed volume of fluid with every revolution or stroke. This makes them inherently better suited for thick fluids because their flow rate is relatively independent of the pressure or viscosity.

1. Internal Gear Pumps

Internal gear pumps are among the most popular choices for viscous applications. They consist of a “gear-within-a-gear” design. As the gears unmesh, they create a vacuum that draws fluid into the pump. As they re-mesh, the fluid is forced out the discharge port.

  • Pros: Excellent for high-viscosity fluids, self-priming, and capable of handling temperatures up to 400°C.
  • Common Uses: Resins, chocolate, asphalt, and fats.

2. External Gear Pumps

External gear pumps use two identical gears rotating against each other. While they are often used for high-pressure hydraulic applications, they are also effective pumps for viscous liquids that are clean and non-abrasive.

  • Pros: High pressure capability, precise flow control, and compact design.
  • Common Uses: Chemical dosing, fuel oils, and polymers.

3. Lobe Pumps

Lobe pumps are similar to gear pumps but the “lobes” do not make physical contact with each other. This lack of contact allows them to handle large solids without damage and makes them ideal for sanitary applications.

  • Pros: Gentle handling (low shear), easy to clean (CIP/SIP), and highly efficient for thick slurries.
  • Common Uses: Yogurt, creams, paper pulp, and pharmaceutical pastes.

4. Progressive Cavity Pumps (PCP)

The progressive cavity pump uses a helical rotor turning inside a double-helix stator. As the rotor turns, it creates “cavities” that move from the suction end to the discharge end. This is arguably the most robust pump for extremely high-viscosity liquids or fluids with high solids content.

  • Pros: Can handle the highest viscosities, provides a smooth, non-pulsating flow, and handles abrasive materials well.
  • Common Uses: Sewage sludge, oil well production, and thick industrial waste.

5. Air-Operated Double Diaphragm (AODD) Pumps

AODD pumps use compressed air to move two diaphragms back and forth. They are versatile, portable, and can run dry without damage. While they have limits on maximum viscosity (usually up to 25,000 cP), they are excellent for utility applications.

  • Pros: Explosion-proof (no electricity), handles solids, and is easy to maintain.
  • Common Uses: Paints, adhesives, and chemical transfer.

6. Peristaltic (Hose) Pumps

In a peristaltic pump, the fluid is contained within a flexible hose or tube. A roller or shoe squeezes the tube, pushing the fluid forward. Because the fluid only touches the inside of the hose, these are perfect for corrosive or abrasive viscous liquids.

  • Pros: No seals or valves to clog, excellent suction lift, and dry-running capability.
  • Common Uses: Mining slurries, lime milk, and abrasive chemical mixtures.

Key Factors to Consider When Selecting Your Pump

Choosing the right pumps for viscous liquids requires more than just looking at a flow rate chart. You must perform a comprehensive analysis of the system requirements.

1. Net Positive Suction Head (NPSH)

Viscous fluids do not flow easily into the suction side of a pump. This can lead to cavitation, where the fluid vaporizes and creates bubbles that implode, damaging the pump. To prevent this, viscous systems often require larger suction piping, slower pump speeds, or even “flooded suction” where the fluid source is located above the pump.

2. Shear Sensitivity

Some fluids change their molecular structure if they are agitated too violently. For example, certain polymers or food products like cream can “break” or change texture under high shear. In these cases, low-speed lobe pumps or progressive cavity pumps are preferred over high-speed gear pumps.

3. Temperature Control

Viscosity is heavily dependent on temperature. A fluid that is pumpable at 80°C might become a solid block at 20°C. Many pumps for viscous liquids come with “jacketing” options, allowing hot water or steam to circulate around the pump casing to keep the fluid at a consistent, flowable temperature.

4. Abrasiveness and Solids Handling

If your viscous liquid contains sand, crystals, or fibers, gear pumps may wear out prematurely. Lobe or progressive cavity pumps with hardened components are better suited for “dirty” viscous fluids.

Industrial Applications of Viscous Fluid Pumps

The need for specialized pumping equipment spans across almost every major industrial sector. Here is how different industries utilize these technologies:

Food and Beverage

Hygiene is the priority here. Pumps must be made of stainless steel and meet FDA or 3-A standards. Lobe pumps are the gold standard for moving peanut butter, fruit concentrates, and dough. Their ability to handle shear-sensitive ingredients without altering the taste or texture is vital.

Oil and Gas

From heavy crude oil to bitumen, the oil industry deals with some of the most challenging viscosities on the planet. Progressive cavity pumps and large-scale internal gear pumps are used to move these materials through pipelines and processing units, often under extreme pressure and temperature conditions.

Chemical and Manufacturing

Adhesives, resins, and paints require precise dosing and consistent flow. Gear pumps are frequently used in these environments because their output is directly proportional to their speed, allowing for exact control in automated manufacturing lines.

Waste Water Treatment

Moving thickened sludge is a daily task in municipal plants. Progressive cavity pumps are the preferred choice here due to their ability to handle high solids content and provide significant suction lift.

Maintenance and Longevity of Viscous Fluid Systems

Pumping thick fluids puts significant mechanical stress on motors, seals, and bearings. To ensure your system remains operational, follow these best practices:

  • Slow Down: Running a pump at a lower RPM reduces internal friction and heat, extending the life of the seals and gears.
  • Oversize the Piping: Reducing the velocity of the fluid in the pipes lowers the pressure drop, making it easier for the pump to do its job.
  • Monitor Seals: Mechanical seals are the most common point of failure. Ensure the seal material is compatible with the fluid and consider using double seals for hazardous or extremely sticky substances.
  • Regular Calibration: For dosing applications, ensure the pump is calibrated regularly as wear on internal components can slightly change the displacement volume over time.

If you are unsure which technology is right for your specific fluid profile, it is always best to consult with experts who understand the nuances of fluid dynamics and mechanical engineering.

[Contact Our Team](https://shop.blazeasia.com/pages/contact) to discuss your specific requirements and find the perfect pumping solution for your facility.

Conclusion

Selecting the right pumps for viscous liquids is a balancing act between fluid physics, mechanical capability, and budget. While the initial cost of a positive displacement pump might be higher than a standard centrifugal pump, the savings in energy, maintenance, and reduced product waste provide a much higher return on investment over the long term.

By understanding the viscosity of your fluid, its shear sensitivity, and the environmental conditions of your plant, you can select a pump that provides reliable, consistent performance for years to come. Whether it is the precision of a gear pump or the ruggedness of a progressive cavity pump, the right tool for the job is out there.

Visit [www.blazeasia.com](https://shop.blazeasia.com) for more information.