Vortex Flow Meter Selection

Vortex meters measure flow by counting the frequency of vortices shed behind a bluff body — the von Kármán effect. They are the go-to choice for steam and gas, robust with no moving parts, but they have a firm low-flow cut-off and dislike viscous or pulsating service. This guide covers where vortex excels, the Reynolds-number limit that trips people up, and how to size it correctly.

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Choose it when

Saturated and superheated steam metering and energy billing
Clean gases — natural gas, compressed air, nitrogen
Clean, low-viscosity liquids in process control
High-temperature service where other technologies struggle
Applications wanting no moving parts and modest cost (£800–£4,000)

Avoid it when

Low flow rates below the Reynolds-number cut-off (no vortices form)
High-viscosity fluids (above ~5–10 cP)
Pulsating or heavily disturbed flow that corrupts vortex shedding
Wide flow ranges — turndown is limited (typically 10:1–20:1)
Slurries or fluids with significant solids

Key selection criteria

Reynolds number / low-flow cut-offVortices only form above a minimum Reynolds number (roughly 10,000–20,000). Below it the meter stops reading — the single most common vortex sizing mistake.

Fluid phaseExcellent for steam and gas; acceptable for clean liquids. Confirm the medium and its cleanliness first.

ViscosityPerformance falls off above ~5–10 cP; viscous fluids damp vortex shedding.

TurndownLimited range (10:1–20:1); size for the normal operating point, not just the maximum.

Straight pipe runsNeeds substantial upstream straight run (15–35 diameters) or a flow conditioner for stable shedding.

Temperature ratingA strength — vortex handles high-temperature steam where many technologies cannot.

Typical applications

Steam accounting and energy billing
Natural gas flow monitoring
Compressed-air energy audits
Clean low-viscosity liquid process control
High-temperature process gas measurement

Limitations to check before specifying

Hard low-flow cut-off — no reading below the minimum Reynolds number
Limited turndown compared with electromagnetic or ultrasonic
Sensitive to upstream disturbance and pulsation
Unsuitable for high-viscosity fluids and slurries

Manufacturers compared

InstruSelect compares published specifications across manufacturers including Emerson (Rosemount), Endress+Hauser (Prowirl), Yokogawa (digitalYEWFLO), Krohne (OPTISWIRL), ABB. Selection is on engineering fit, not brand; mention of a manufacturer is factual reference, not endorsement.

Frequently asked questions

Why does a vortex meter stop reading at low flow?

Vortices only shed above a minimum Reynolds number (around 10,000–20,000). Below that threshold no stable vortices form, so the meter has a genuine low-flow cut-off — you must size it so the minimum operating flow stays above the limit.

Is vortex a good choice for steam?

Yes — vortex is one of the best technologies for saturated and superheated steam, combining high-temperature capability, no moving parts and good repeatability for energy billing.

Can vortex meters handle viscous liquids?

No. Above roughly 5–10 cP the viscosity damps vortex shedding and accuracy collapses. For viscous fluids choose Coriolis or electromagnetic instead.

Compare this against other technologies

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