When selecting an industrial pump, one of the most important factors to consider is the viscosity of the fluid being transferred.
Viscosity refers to a liquid’s resistance to flow caused by internal friction within the liquid. Simply put, the thicker the liquid, the higher the viscosity.
Low viscosity fluids such as water, milk, beer, solvents and some chemicals flow easily through pipework with minimal resistance. High viscosity fluids such as honey, molasses, syrups, oils, sludge, paint, adhesives and creams move more slowly and require greater force to pump efficiently.
Choosing the correct pump for viscous fluids or low viscosity liquids is essential for maintaining flow performance, reducing wear, improving energy efficiency and preventing downtime.
Why viscosity matters for pump performance
Fluid viscosity directly affects how a pump performs. As viscosity increases, friction losses within the pipework and pump also increase. This can reduce flow rates, increase pressure requirements and place additional load on the motor.
For low viscosity applications, pump selection is usually straightforward. However, selecting the best pump for high viscosity fluids requires careful consideration of the liquid properties, operating temperature, pipe size, suction conditions and desired flow rate.
Temperature can also dramatically change viscosity. Many high viscosity products become thinner as they are heated, making them easier to transfer. Some fluids are also thixotropic, meaning they become less viscous when stirred, mixed or agitated.
Best pumps for low viscosity fluids
Centrifugal pumps are generally the preferred low viscosity pump solution because they are designed to efficiently transfer thin liquids at high flow rates.
These pumps perform best when handling fluids with viscosity similar to water. Common applications include:
- Water transfer
- Chemical circulation
- Beverage processing
- Cooling systems
- CIP systems
- Irrigation and washdown
For slightly thicker liquids, industrial centrifugal pumps may still perform adequately, although efficiency can begin to decline. As viscosity increases further, centrifugal pump performance drops significantly, resulting in reduced flow and head pressure alongside increased power consumption.
Best pumps for high viscosity fluids
When handling thicker products, positive displacement pumps are usually the most effective solution. Unlike centrifugal pumps, these pumps move a fixed volume of liquid with each rotation or cycle, making them ideal pumps for high viscosity fluids.
The best pump for high viscosity fluids will depend on the product characteristics, solids content, flow rate and pressure requirements.
Air operated double diaphragm (AODD) pumps are highly versatile and can handle low, medium and moderately high viscosity fluids. They are commonly used for chemicals, paints, wastewater, oils and food products because they are self-priming, can run dry and are capable of passing solids.
Progressive cavity pumps, also known as helical rotor pumps, excel when handling very high viscosity, shear-sensitive or solids-laden products. Their smooth, low-pulsation flow makes them ideal for sludge, thick oils, adhesives, polymers and food pastes.
Peristaltic pumps are often selected for abrasive, corrosive and high-solids applications. Because the fluid only contacts the hose, they provide gentle product handling, accurate dosing and simplified maintenance. A high viscosity peristaltic pump can be an effective solution for slurries, chemicals, wastewater and viscous industrial products.
Gear pumps are commonly used for clean, high viscosity liquids such as oils, lubricants, resins and syrups where a consistent flow rate is required.
Rotary lobe pumps are well suited to food, beverage and pharmaceutical applications involving viscous or shear-sensitive products.
Dosing and metering pumps can be used where accurate chemical injection or controlled dosing of higher viscosity liquids is required.
Typical high viscosity applications include:
- Honey and syrups
- Paints and coatings
- Sludge and wastewater
- Oils and lubricants
- Adhesives and polymers
- Food pastes and creams
- Cosmetic products
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Why peristaltic pumps work well for viscous fluids
Peristaltic hose pumps are among the most reliable and low-maintenance solutions for demanding industrial applications. They operate by compressing a flexible hose or tube using rotating rollers or shoes to move fluid through the pump. As the fluid only comes into contact with the inside of the hose, these pumps are ideal for handling abrasive, corrosive, shear-sensitive and high solids media.
A high viscosity peristaltic pump offers several advantages:
- Excellent suction lift capability
- Dry-run capability without damage
- Gentle, low-shear fluid transfer
- Accurate and repeatable dosing
- Reversible flow direction
- Efficient handling of solids and slurries
- Reduced maintenance due to the absence of seals and valves
These characteristics make them an effective high viscosity pump solution, as well as a versatile pump for viscous fluids across industries such as mining, wastewater treatment, food processing and chemical manufacturing.
Pumping high viscosity oils and industrial liquids
Selecting the right high viscosity oil pump depends on the oil’s thickness, temperature and required flow rate.
For heavy oils, lubricants and greases, positive displacement technologies such as gear pumps and peristaltic pumps are commonly used because they can maintain stable flow under higher pressure conditions.
A suitable high viscosity liquid pump should be capable of:
- Maintaining steady flow despite changing viscosity
- Operating efficiently at lower speeds
- Minimising shear on sensitive products
- Handling variable temperatures
- Reducing cavitation risk
In many industrial applications, a peristaltic pump for high viscosity fluids is preferred because it can accommodate fluctuating viscosities without damaging the product.
Important considerations when pumping viscous fluids
There are several additional design considerations when selecting a pump for high viscosity fluid applications.
Ensure proper suction conditions
High viscosity liquids do not flow easily into the pump inlet. Any restriction on the suction side can significantly affect performance, so pipework should be designed to minimise pressure losses. In most cases, a flooded suction arrangement is recommended to ensure reliable pump priming, maximise efficiency and reduce the risk of cavitation.
Increase pipework size where necessary
Because viscous fluids create higher friction losses than low viscosity liquids, larger suction and discharge pipework may be required. Increasing pipe size helps reduce drag, minimise pressure loss and maintain the desired flow rate throughout the system.
Account for power requirements
As viscosity increases, the pump requires more torque and power to move the product. Correct motor sizing is critical to prevent overloading and ensure consistent operation.
Consider temperature changes
If the product temperature fluctuates, viscosity can change dramatically. This may affect flow rates, pressure requirements and dosing accuracy. Many high viscosity products become easier to pump as temperature increases.
Understand viscosity measurements
Viscosity is commonly expressed in units such as centistokes (cSt) or Saybolt Universal Seconds (SSU). Knowing the viscosity of the liquid being pumped is essential for accurate pump selection. Manufacturers use viscosity correction charts to predict how different pump types will perform with specific fluids, helping ensure the selected pump can deliver the required flow and pressure.
Choosing the best pump for your application
There is no single universal best pump for high viscosity fluids because every application is different. The ideal solution depends on:
- Fluid viscosity
- Flow rate requirements
- Operating pressure
- Temperature
- Solids content
- Shear sensitivity
- Chemical compatibility
- Dosing accuracy requirements
For low viscosity liquids, centrifugal pumps often provide the most economical solution. For thicker products, positive displacement pumps can deliver superior performance, reliability and efficiency.
By understanding your fluid viscosity and system requirements, pump performance can be accurately predicted using viscosity correction data and pump-specific performance curves. This helps ensure the selected pump will operate efficiently and reliably in your application.
Need help selecting a pump for viscous fluids?
Global Pumps can help you select the right solution for your application. Our experienced team can assess your product viscosity, pipework configuration, flow requirements and operating conditions to recommend the most suitable pump technology for long-term performance and efficiency.
Get in touch with Global Pumps today to discuss your application.
