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Aerofoil Flow Meter: Low Pressure Drop Differential Pressure Senses
Quick Answer: An aerofoil flow meter from Silver Instruments measures air, gas, steam, and clean liquid flow. It uses low pressure drop differential pressure sensing across an aerofoil shaped element. It gives a stable flow signal with very low permanent pressure loss. This meter suits compressed air, natural gas, steam, and energy metering applications where pressure loss is a direct operating cost.
What Is an Aerofoil Flow Meter
An aerofoil flow meter is a differential pressure primary element installed between flanges or inserted into a pipe. The sensing bar has an aerofoil cross section similar to a small wing. Fluid passes around the profile. A high pressure port faces upstream. A low pressure port reads from the downstream side. The difference between these two pressures gives flow rate.
Silver Instruments builds aerofoil flow meters for line sizes from DN50 to DN1200. Typical accuracy for gas and steam is plus or minus 1 percent of rate when paired with a good DP transmitter. Repeatability is usually better than plus or minus 0.25 percent. Many customers order the complete package with a Silver Instruments DP transmitter and a flow computer.
Why Low Pressure Drop Matters More Than Accuracy in Some Plants
An orifice plate can work but it wastes energy. A beta ratio 0.6 orifice plate may lose 40 to 60 percent of its differential pressure permanently. In a compressed air line running at 7 bar, that wasted pressure costs real power. Aerofoil meters are different. Permanent pressure loss is often 5 to 15 percent of the measured differential pressure. In practice, a 100 mbar DP reading may cause only 8 to 12 mbar permanent loss.
We have seen this on customer sites many times. A paint manufacturer in Southeast Asia replaced three orifice plates on compressed air headers. Their air compressor discharge pressure dropped by 0.4 bar. That one change reduced energy spend by enough to recover the meter cost in less than nine months.
How Differential Pressure Sensing Works
The aerofoil profile creates a controlled low pressure zone. A DP transmitter measures the high side and low side. The transmitter converts that signal to 4-20 mA HART. The flow computer calculates flow rate using a square root function and line pressure and temperature compensation.
For saturated steam, we recommend adding a PT100 temperature sensor and a pressure transmitter. For natural gas, use pressure and temperature compensation. The calculation can run in a Silver Instruments flow computer or in the plant DCS.
Here is the thing. The insertion length and pipe internal diameter must match. If the wrong insertion length is ordered, the low pressure port can sit outside the flow profile. That causes unstable readings at low flow.
Field Cases and Common Applications
Aerofoil flow meters fit compressed air, natural gas, steam, biogas, and clean water. They are not ideal for slurry, high viscosity oil, or fluids with heavy solids. For those services Silver Instruments offers electromagnetic, oval gear, or Coriolis mass flow meters.
Last year a customer in Vietnam asked us for a steam meter for a 150 mm line. Steam pressure was 8 bar and temperature was 190 °C. We supplied
A natural gas line at a glass bottle plant in Mexico uses a DN200 aerofoil meter. Line pressure is 4 bar. The customer needed low blockage and low maintenance. The meter has operated for 18 months with no drift.
Specification Checklist for Engineers
Send us your pipe size, fluid, pressure, temperature, minimum and maximum flow rate, and whether you need hot tap insertion or flanged installation. For gas lines, include density or gas composition. For steam, state saturated or superheated and exact pressure. For air, state whether flow is normal cubic meters per hour or standard cubic feet per minute. A clear unit prevents misquotes.
Silver Instruments can supply the meter element alone, or a complete assembly with DP transmitter, manifold valve, and flow computer. If the transmitter will be mounted in ATEX Zone 1, tell us. We can supply Ex d or Ex ia versions.
Recommended Model Pairing
For compressed air and inert gas, pair the Silver Instruments AFT-200 aerofoil flow element with a Silver Instruments SDP-305 differential pressure transmitter. Range 0 to 100 mbar, 4-20 mA HART output, stainless steel wetted parts. For steam up to 350 °C, use the AFT-200 with a compact manifold and steam rated diaphragm seals.
For line sizes below DN80, we often recommend a thermal mass flow meter or vortex meter instead. The aerofoil element needs enough straight run. Typical upstream straight pipe requirement is 10D. Downstream straight run is 5D. If your pipe has limited straight run, send a sketch and we will check the uncertainty.
FAQ
Can an aerofoil flow meter measure liquid?
Yes, clean liquids with low viscosity work. Aerofoil elements are used on water lines from DN50 to DN1200. For dirty water with solids above 1 percent, choose an electromagnetic flow meter.
What is the typical permanent pressure loss?
Permanent pressure loss is normally 5 to 15 percent of differential pressure. For a 50 mbar DP reading, loss is often under 7 mbar. This is much lower than an orifice plate.
What pipe sizes does Silver Instruments offer?
We offer DN50 to DN1200 as standard. Larger sizes are possible for flue gas and large air ducts on request.
Do I need a temperature sensor for compressed air?
Not always. For energy management, we recommend pressure compensation at minimum. For standard volume flow, add a PT100 and pressure transmitter.
What is the difference between an aerofoil flow meter and an averaging pitot tube?
Both are differential pressure insertion devices. An aerofoil profile has lower permanent pressure loss and better signal stability at low flow. The price difference is small in most sizes.
For a quote on an aerofoil flow meter for compressed air, steam, or natural gas, send your pressure in bar, temperature in °C, pipe size in DN, and flow range. Contact Silver Automation Instruments at Tel +86 25 68650347 or WhatsApp +86 25 52155837. WeChat +86 15365082610. You can also visit flow-meter.com.au for product data sheets.
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