, a Nanjing-based supplier of industrial flow, level and pressure instrumentation, has published a technical guide on how to select a high-viscosity oil flow meter. The guide is written for engineers who meter high visocsoity liquid ,such as heavy fuel oil, lubricants, hydraulic oil, resins and other liquids above 200 mPa·s.

Between January 2025 and Sep 2026, the company received 3000 flow meter inquiries from 130 countries. 8% involved oils or liquids above 200 mPa·s, mainly from heavy fuel oil and marine fuel, bitumen, molasses and syrups, mineral slurries, coating slurries and epoxy resins. These cover the oil and gas, marine, road construction, food processing, mining, coatings and chemical industries. Most of them are trading agents and engineering integrators.

Why viscosity changes the choice

Viscosity is the first parameter to check. Many common flow sensor types lose accuracy as it rises. Turbine flowmeters slow down or break down as fluid drag increases. Vortex flowmeters need a minimum Reynolds number that thick oil rarely reaches. Electromagnetic meters cannot measure oil, because oil is not conductive liquid.

Positive displacement flow meters behave the other way. Thicker oil leaks less between the gears and the housing, so slip drops and accuracy holds. The trade-offs are higher pressure loss and a narrower usable flow range.

Coriolis mass flow meters take a third route. The flow sensor measures high viscosity liquid mass flow directly from the twist of vibrating tubes, so viscosity does not change the measuring principle. The same flow sensor also reads density and temperature. There are no moving parts to wear, and no inlet or outlet straight runs are required. Accuracy ranges from ±0.1% to ±0.5% of flow. Thick oil raises the pressure loss across the tubes, so the flow sensor is often sized one step larger than the line. That sizing should be calculated from the actual viscosity, not read from a standard flow table.

Key data from the guide

• Oval gear flow meters handle viscosity up to 2,000 mPa·s at 0.5% or 0.2% accuracy, in sizes 1/8 inch to 8 inches.
• Helical gear flow meters extend the limit to 3,500 cP with low pressure loss, and max size is 14 inches(DN350)
• Coriolis mass flow meters measure mass directly and are not affected by viscosity. Accuracy ranges from ±0.1% to ±0.5%. Sizing must account for the higher pressure drop of thick liquids.
• Flow range shrinks as viscosity rises. A DN50 oval gear meter covers 8 to 24 m³/h on light oil, but only 1.2 to 12 m³/h at 1,000 to 2,000 mPa·s.
• Heated oil needs a high-temperature radiator. With this option, oval gear meters reach 200°C and helical gear meters reach 250°C. A heating jacket keeps oil from setting inside the meter body.

"Most selection errors we see come from sizing by pipe size, not by viscosity at operating temperature," said Ellen Sheng, Sales Engineer of Silver Automation Instruments. "A meter sized for diesel can be too small for the same flow of heavy fuel oil. We wrote this guide so engineers can check that before they send an RFQ."

The guide closes with a five-point checklist: viscosity at the lowest operating temperature, flow range at that viscosity, allowable pressure loss, process temperature, and required output (pulse, 4-20mA, HART or RS485).

The full guide is available on the Silver Automation Instruments website. Engineers can also submit process data for free meter sizing.
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About Silver Automation Instruments Ltd.

Silver Automation Instruments Ltd. is an industrial instrumentation supplier based in Nanjing, China. The company supplies oval gear, Coriolis, turbine, electromagnetic, vortex and thermal mass flow meters, together with pressure transmitters, level meters and paperless recorders. It serves B2B buyers in 130 countries. Learn more at www.silverinstruments.com.

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