A Comprehensive Guide to High Viscosity Flow Meters

Measuring the flow of high viscosity liquids is one of the most demanding tasks in industrial instrumentation. Fluids such as heavy oils, asphalt, resins, and molasses are thick, difficult to pump, and present unique challenges for accurate measurement. Unlike low viscosity fluids like water or milk that flow easily, these thick liquids require specialized flow meter technologies to ensure process efficiency, product consistency, and reliable inventory management. An incorrect meter choice can lead to inaccurate readings, high pressure drops, and even complete measurement failure.

This guide provides an in-depth analysis of the best flow meter technologies for high viscosity fluids. We will compare the two primary solutions—Coriolis mass flow meters and Oval Gear positive displacement meters—and explore their ideal applications across various industries, helping you select the perfect instrument for your challenging process.

The Unique Challenge of Measuring Viscous Fluids

the rotors of turbine flow meter can be broken by high viscosity liquid

High viscosity creates several problems for standard flow meters. Velocity-based technologies, such as turbine or orifice plate meters, rely on a uniform, turbulent flow profile to function correctly. Viscous fluids, however, often exhibit laminar flow, where the fluid moves faster at the center of the pipe than at the edges. This non-uniform profile can lead to significant inaccuracies. Furthermore, the thick nature of the fluid can clog or damage the moving parts of mechanical meters, leading to frequent maintenance and downtime.

Primary Technologies for High Viscosity Flow Measurement

Coriolis flow meter and oval gear flow meter for high viscosity liquid 

For decades, two technologies have proven to be the most reliable and accurate for handling viscous fluids: Positive Displacement meters (specifically Oval Gear) and Coriolis Mass Flow Meters.

Coriolis Mass Flow Meters: The Ultimate Solution for Viscous Fluids

Coriolis flow meter for high visocosity liquid

Advantages of Coriolis Meters for High Viscosity Fluids:

• Direct Mass Measurement: Provides the most accurate measurement (often ±0.1%) as it measures true mass, eliminating the need for process condition compensation.
• Handles Solids and Slurries: The open, obstructionless tube design allows Coriolis meters to measure fluids with suspended particles, making them ideal for slurries.
• Extreme Viscosity Range: They can measure fluids with viscosities up to 500,000 cP and beyond.
• No Flow Conditioning Required: They do not require straight pipe runs for installation, making them versatile for compact spaces.
• Multi-Parameter Measurement: A single Coriolis sensor can simultaneously measure mass flow, volumetric flow, density, and temperature.

Disadvantages of Coriolis Meters:

• High Cost: They are the most expensive flow meter technology, representing a significant initial investment.
• Pressure Drop: The design of the vibrating tubes can cause a pressure drop, which increases sharply with viscosity and may require more powerful pumps.
• Vibration Sensitivity: They can be sensitive to external pipe vibrations if not installed and supported correctly.

Oval Gear Flow Meters: The Reliable Choice for Clean Viscous Liquids

Oval gear flow meter for high viscosity liquid measurement

Oval Gear meters are a type of Positive Displacement (PD) flow meter. They function like a highly precise fluid engine, using two interlocking gears to trap and pass a precise, known volume of liquid with each rotation. Because they directly measure volume, they are highly accurate and largely unaffected by the fluid's viscosity.

Advantages of Oval Gear Meters for High Viscosity Fluids:

• High Accuracy: They offer excellent accuracy (typically ±0.5%) across a wide range of viscosities.
• Low Pressure Drop: They are designed to be efficient, creating minimal pressure loss in the system.
• No Power Required: Mechanical versions with a register display can operate without any external power supply, making them ideal for remote or hazardous locations.
• Lower Cost: For clean fluid applications, a carbon steel oval gear meter is a significantly more cost-effective solution than a Coriolis meter.
• Simple Installation: They do not require straight pipe runs and can be installed in tight spaces.

Limitations of Oval Gear Meters:

• Not for Solids: The tight tolerances of the gears mean they are only suitable for clean liquids without suspended particles or solids, which can cause jamming and damage.
• Moving Parts: The rotating gears are subject to wear over time and require periodic maintenance.
• Bulky at Large Sizes: Large-diameter oval gear meters can be very heavy and bulky, increasing shipping and installation costs.

Special Consideration:Small Oval Gear Meters for Low Flow Rates

Small flow meter for high viscosity liquid measurement

For applications that require precise measurement of high viscosity fluids at very low flow rates—such as chemical dosing, additive injection, or in laboratory settings—the small oval gear flow meter is an ideal solution. These compact positive displacement meters operate on the same reliable principle as their larger counterparts but are specifically engineered for flow ranges often below 1 L/min. They provide a highly accurate, cost-effective alternative to Coriolis meters for small-volume, high-viscosity applications where the fluid is clean. Below video to show how our small oval gear flwo meter work for the high visocisty liquid flow measurement:

Quick Selection Guide & Comparison Table

Choosing between these two excellent technologies depends on your specific application. Here are three simple rules to guide your decision:

1. For **clean liquids with a viscosity below 2000 cP** where a cost-effective and accurate solution is needed, the **Oval Gear Flow Meter** is often the ideal choice.
2. For fluids with **any level of viscosity** or those **containing solids/slurries**, or when direct **mass flow** measurement is required for critical process control, the **Coriolis Mass Flow Meter** is the superior and necessary solution.
3. For **very low flow rate** applications, both **small Oval Gear meters** and **micro-Coriolis meters** provide excellent, high-accuracy solutions.

High Viscosity Flow Meter Applications by Industry

High viscosity flow meters are essential in a wide range of industries across the globe. Below are some of the most common applications where our instruments provide critical data.

Oil & Gas Industry

Measuring heavy fuel oil, crude oil, alkyd oil and lubricants requires robust meters. Coriolis meters are vital for custody transfer of crude oil, while oval gear meters are a reliable choice for fuel dispensing and consumption monitoring.

Food & Beverage Industry

Hygienic Coriolis meters are used to accurately measure the mass of thick food products like chocolate, honey, cream, and syrups, palm kernel oil ensuring consistent recipe batching and product quality.

Chemical Processing

The chemical industry relies on high-accuracy meters for dosing resins,glucose, lecithin, polymers, solvents,grease, paste and other viscous chemicals. The material compatibility of Coriolis and stainless steel oval gear meters is critical in these applications.

Power Generation & Heavy Industry

Precise fuel oil measurement is crucial for efficiency in industrial furnaces and boilers, ensuring optimal combustion and cost control. This often involves thick, pre-heated oils that are easily handled by Coriolis or oval gear meters.

Pulp & Paper Industry

In paper mills, Coriolis meters are used to measure the flow of thick paper pulp slurries and coating chemicals, where other meters would quickly clog and fail.

High Temperature Processes

Many viscous fluids, like asphalt and bitumen, must be measured at extreme temperatures. Our specialized high-temperature flow meters, particularly Coriolis models, are engineered to handle these demanding conditions with exceptional reliability.

Conclusion: Choosing Your High Viscosity Flow Meter

The successful measurement of high viscosity fluids hinges on selecting the right technology for your specific process. While an oval gear meter provides a cost-effective, high-accuracy solution for clean liquids, the Coriolis mass flow meter offers unmatched versatility for the most challenging applications involving slurries, extremely high viscosities, or the need for direct mass measurement.

At Silver Automation Instruments, we specialize in providing robust solutions for even the most difficult flow applications. Our team of experts can analyze your process data and help you choose the ideal instrument to deliver the accuracy and reliability you demand.