Pumping High-Viscosity Fluids: Best Practices for System Design and Pump Selection

Key Takeaways: 

• High-viscosity fluids can be successfully pumped when the pump and system are configured for the application.
• Larger tubing, lower pump speeds, pressure-fed inlets, and temperature control can improve the handling of viscous liquids.
• Pump selection is application specific. Factors such as flow rate, fluid properties, and system design all influence performance.
• Fluid Metering(FMI) offers application-specific pump configurations, including optional heated pump heads designed to support high-viscosity fluid applications.

Successful Pumping Starts with the Right System Design

When engineers begin designing a fluid handling system, one of the first questions is often whether a pump can reliably handle a high-viscosity fluid. The answer is yes, but success depends on selecting the right pump and optimizing the overall fluidic system for the application.

Unlike low-viscosity liquids, viscous fluids require more force to move through tubing, fittings, and pump components. If the system is not designed with these characteristics in mind, flow restrictions can reduce performance and place unnecessary stress on the pump. Rather than viewing viscosity as a limitation, it should be treated as one of the key engineering parameters that influences pump selection, system layout, and operating conditions.

What is Viscosity?

Viscosity describes a fluid's resistance to flow.

Low-viscosity fluids flow readily because their molecules move past one another with relatively little resistance. These fluids typically travel through tubing with minimal effort. High-viscosity fluids behave differently. They flow more slowly, resist deformation, and may require additional force to move through a pumping system. As viscosity increases, so does the importance of proper system design.

Understanding this relationship is one of the first steps in selecting the right pump for reliable fluid dispensing.

How Viscosity Affects Pump Performance

Higher viscosity influences more than just the pump itself, it affects the entire system.

As viscosity increases, engineers should consider:

System Component Effect of Higher Viscosity

These considerations highlight why pump selection should always be evaluated within the context of the complete system rather than as an isolated component.

Can FMI Pumps Handle High-Viscosity Fluids?

Yes. However, successful pumping depends on selecting the appropriate pump configuration for the specific application.

One important consideration is flow rate. Applications requiring very high flow rates may be more challenging because viscous fluids naturally resist flow through the system.

Instead of focusing solely on the pump, engineers should evaluate:

• Required flow rate

• Tubing selection

• Pump operating speed

• Inlet conditions

• Fluid temperature

Together, these variables have a significant impact on overall pumping performance.

Engineering Best Practices

1. Increase Tubing Size

   Using tubing that is too small creates unnecessary flow restrictions before the fluid reaches the pump. Larger tubing provides a less restrictive flow path, helping viscous liquids move more effectively through the system.

2. Reduce Viscosity with Temperature

   Heating the fluid, particularly on the inlet side, can decrease viscosity and improve flow characteristics. For applications that benefit from thermal management, FMI offers pump head options designed to help maintain fluid temperature during pumping.
   

    

3. Use a Pressure-Fed Inlet
   Applying pressure at the inlet helps move viscous fluids through the tubing and into the pump head. This additional assistance can improve overall system performance when handling more viscous liquids.

4. Operate at Lower rpm
   Pump speed has a direct influence on system performance.

Operating at approximately 400 rpm or below, when appropriate for the application, can:

• Reduce stress on the pump

• Reduce stress on the motor

• Allow viscous fluids to move more effectively through the system

Common Mistakes When Pumping Viscous Liquids

Several common design decisions can reduce pumping performance.

Avoid:

• Using tubing that is too small
• Operating at excessively high pump speeds 
• Operating without inlet pressure when pressure feed is beneficial
• Ignoring the advantages of temperature control for suitable applications  

These conditions can increase system strain and reduce pumping efficiency.

Selecting the Right Pump for High-Viscosity Fluids

No single pump is the best choice for every viscous fluid application.

Selecting the right pump requires evaluating the complete operating environment, including:

• Fluid viscosity

• Required flow rate

• Tubing configuration
• Operating speed
• Temperature
• Inlet conditions

Considering these factors together helps engineers develop a fluidic system that supports reliable, repeatable operation.

The Bottom Line

High-viscosity fluids present unique engineering challenges, but they can be pumped successfully with the right system design and pump configuration. By considering tubing size, operating speed, inlet pressure, and temperature early in the design process, engineers can improve fluid movement and support more reliable system performance.

If you're evaluating a high-viscosity fluid application, Fluid Metering's engineering team can help determine the most appropriate pump configuration based on your operating requirements and application goals.