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Pitot Flow Meter: Differential Pressure Gas Velocity Sensors
Quick Answer: A pitot flow meter measures gas velocity by converting the difference between total pressure and static pressure into a flow rate. It works best in large ducts, stacks, and pipes carrying clean or slightly dusty air, flue gas, or natural gas. Silver Instruments supplies averaging pitot tubes that deliver ±1% repeatability and very low permanent pressure loss for pipe sizes from DN50 to DN3000.
We frequently ship these sensors to LNG terminals in Southeast Asia, cement plants in the Middle East, and steel mills in Latin America where natural gas, combustion air, and process off-gas need accurate volumetric flow tracking.
How a pitot flow meter actually works on your gas line
An averaging pitot tube sits inside the pipe and faces the flow. Multiple upstream holes sense total pressure. Downstream holes sense static pressure. The differential pressure transmitter reads the difference and outputs a 4-20 mA HART signal proportional to the square of the velocity. A flow computer or PLC calculates the actual flow using your gas composition, temperature, and pressure.
In practice, most engineers skip the explanation and look at the numbers. If you send us your gas type, pressure in bar, temperature in °C, pipe inside diameter in mm, and typical flow range in kg/h or Nm³/h, we will propose a complete pitot flow meter assembly with the DP transmitter sized and calibrated for your operating window.
Where pitot flow meters outperform other gas meters
Thermal mass meters struggle with wet or dirty gas. Vortex meters add pressure drop you cannot afford on a low-pressure flare line. Orifice plates require cutting pipe and welding flanges. A hot-tapped averaging pitot tube inserts through a 38 mm ball valve while the line remains under pressure. That saves a shutdown on a 600 mm combustion air duct at a power plant.
We have seen a paint manufacturer in Vietnam replace their insertion thermal probes with a Silver Instruments pitot flow meter because the hot drying air contained solvent traces that fouled the heated sensor. The pitot sensor with constant purge kept working. They now check the 4-20 mA output once a week and clean the impulse lines once a quarter.
Gas types and industries that use our pitot meters
Natural gas distribution stations in Nigeria use our pitot tubes on 150 mm and 200 mm lines for custody transfer monitoring, paired with a PT100 and pressure transmitter for full compensation. Cement plants in Oman measure primary air and secondary air to the kiln on ducts from 800 mm to 2200 mm. We supply stainless steel 316L probes with ceramic-coated tips where the dust load exceeds 5 g/Nm³. Chemical plants in Thailand meter nitrogen, oxygen, and hydrogen mixtures in 50 mm to 100 mm pipes for reactor feeding. The all-welded construction avoids leak points on hydrogen service.
For flue gas desulfurization (FGD) outlets in coal-fired power stations in Indonesia, we recommend Hastelloy C276 sensor material and a remote diaphragm seal DP transmitter to handle acid dew point corrosion below 120 °C.
Key specifications you need before you request a quote
Most inquiries we receive miss the pipe internal diameter. The exact ID matters more than the nominal size. A 10-inch schedule 40 pipe has an ID of 264.6 mm. A schedule 80 pipe has 247.6 mm. That changes the flow area by 12% which directly impacts the calculated velocity. Also provide gas composition or molecular weight, moisture content, and dust load if any. These three values determine whether we supply a standard blockage T-type sensor, a constant purge system, or a fully welded cleaning port design.
Typical specifications we work with:
Pipe sizes: DN50 to DN3000
Pressure rating: up to PN40 standard, PN100 on request
Temperature range: -40 to 600 °C with appropriate material and DP transmitter mounting
Output signal:
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Approvals: ATEX Zone 1, IECEx, SIL 2 capable on the DP transmitter
Installation details many manuals skip
The straight-run requirement is 7 pipe diameters upstream and 3 downstream for a standard averaging pitot. But on a real site, you rarely get that luxury. A brewery in South Africa needed a CO₂ flow meter on a 65 mm line right after a 90-degree elbow. We machined a custom sensor with a flow profile correction factor based on their Reynolds number range. The total error came under ±2% of actual flow. Without the correction, they would have seen a 12% under-read in their fermentation gas recovery system.
Hot tapping is straightforward when you have a qualified technician and the right ball valve assembly. We ship the probe with a welded thread-o-let, a full-bore ball valve, and a drilling guide. A diesel generator set factory in Singapore installed our pitot meter on a 500 mm exhaust gas duct without plant shutdown. The total installation took under two hours from initial weld to final signal check.
Pitot flow meter vs. other DP primary elements
Averaging pitot tubes cause much less permanent pressure loss than an orifice plate. On a 300 mm air line flowing 5 kPa pressure, an orifice plate might drop 500 Pa permanently. Our pitot tube drops under 50 Pa. That saves compressor power costs year after year. Venturi tubes also have low pressure loss but are expensive for large diameters and hard to retrofit. Annubar-type pitot tubes work on similar principles. We supply a direct equivalent with interchangeable head and high-pressure isolation valve certified to ANSI B16.34.
FAQ
Can a pitot flow meter measure liquid flow? It can, but we almost always recommend a full-bore electromagnetic flow meter instead. Pitot tubes work in clean liquids where a Coriolis or magmeter is not practical due to budget or size constraints. For gas, however, the pitot is often the best first choice.
Do I need a DP transmitter or can I use a mechanical DP gauge? You can use a DP gauge for local indication only, but you lose temperature and pressure compensation, so the reading is only accurate at design conditions. Most customers choose a multivariable DP transmitter with built-in compensation and Modbus output.
How often do I clean the sensor? For clean natural gas or instrument air, annual inspection is enough. For flue gas or air with dust, we recommend quarterly visual checks and purging the impulse lines. Platinum RTD sensors in the probe tip can detect clogging by monitoring temperature shift.
What is the minimum gas density for reliable measurement? A practical lower limit is around 0.5 kg/m³ at operating conditions, which covers natural gas at low pressure. Below that, the differential pressure becomes too small for a standard DP transmitter to resolve without significant uncertainty. Thermal mass meters often work better for very low-density gases like hydrogen at atmospheric pressure.
Do you supply the complete meter run with straight pipe spools? Yes, we weld the pitot tube into a flanged spool piece up to DN600. This guarantees the correct installation orientation and eliminates field welding alignment errors. We also include the flange drillings to DIN, ANSI, or JIS standards based on your local requirements.
Ready to get a specific price and delivery time?
Send us your pressure (bar), temperature (°C), pipe inside diameter (mm), gas type, and flow range (kg/h or Nm³/h) to [email protected]. For faster response, WhatsApp us at 86-135-12131526 or call +86-135-1213-1526. We will reply with a technical datasheet and a formal quote within 24 hours for standard configurations. We ship pitot flow meters from our factory in China to Australia, Southeast Asia, the Middle East, Africa, and South America by DHL, FedEx, sea freight, or air freight based on your project schedule.
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