Pitot Tube Flow Sensors: Multi-Port Insertion Elements for HVAC Duct Networks

Quick Answer: Multi-port averaging pitot tube sensors measure HVAC duct air flow by averaging differential pressure from several impact and static ports. Silver Instruments supplies the SPT-240 insertion series for ducts from DN100 to DN2000, with 4-20 mA HART output, accuracy of plus or minus 1.5 percent of rate, and temperature ratings up to 150 °C. Send your duct size, air velocity, and temperature to get a same-day quote.

HVAC engineers and commissioning teams often skip a simple fact. A single-point pitot tube misses most of the velocity profile in a large supply air duct. Multi-port insertion elements solve that problem. They use several sensing holes across the duct cross section. The result is a stable differential pressure signal that works well for building automation systems.

When Multi-Port Sensors Beat Single Point Devices

In a duct of DN800 or DN1000, air velocity is not uniform. The profile changes after bends, filters, dampers, and fan outlets. A single impact port reads only one spot. A multi-port averaging pitot tube takes the average of 4 to 16 points. That average is closer to the true duct flow. For HVAC networks, the result is fewer false alarms and better energy monitoring.

Most engineers skip this part: straight run matters. We recommend 4 duct diameters upstream and 2 downstream for a multi-port sensor. If you have less straight run, the SPT-240 still works but you should field calibrate the transmitter.

Output Signals and Pressure Ranges

Most HVAC control panels accept 4-20 mA or 0-10 V DC. Silver Instruments offers both. The typical differential range is 0 to 500 Pa for air velocities from 2 to 20 m/s. For high velocity ducts up to 40 m/s, we configure a 0 to 2500 Pa range. The transmitter can be mounted directly on the sensor or remotely. HART protocol is available for loop diagnostics and remote range changes.

Installation in Round and Rectangular Ducts

Installation is straightforward. For round ducts of DN300 to DN1200, the sensor body inserts through a 25 mm or 50 mm weld nipple. For rectangular ducts, the insertion length matches the internal width. You can mount the sensor horizontally or vertically. Most commissioning engineers prefer the horizontal position for liquid condensation drainage. We ship each unit with a compression fitting, identification tag, and a quick start guide.

Field Results from HVAC Projects

Last year, a chiller plant contractor in Vietnam ordered 18 SPT-240 sensors for a pharmaceutical warehouse. Duct sizes ranged from DN600 to DN1400. Air temperature was 12 to 18 °C. The customer required 4-20 mA HART signals to integrate with a Siemens BAS. We calibrated each sensor for a 0 to 800 Pa range. The plant passed commissioning on the first attempt.

In Australia, a hospital HVAC upgrade used our insertion sensors on outside air intakes. The ducts carried 35 °C summer air and condensation was a risk. We supplied 316L stainless steel sensors with PT100 temperature elements built in. That single insertion point delivered air flow and temperature to the building management system.

We have seen this on customer sites many times. A balancing contractor in Manila installed single-point pitot tubes on a DN700 return air duct. The BAS reading jumped every time a VAV box opened or closed. We replaced them with SPT-240 multi-port elements. The signal became stable within one minute.

How to Request a Quote

Send us your duct size (DN or internal width in mm), air velocity range (m/s), operating temperature (°C), and required output signal. We will recommend a model, a differential pressure range, and an insertion length. Contact Silver Instruments at Tel +86-25-68650347, WhatsApp +86-25-52155837, or WeChat +86 15365082610.

Do not send a single-line enquiry with no process data. We need the four values above. Supplying those four values saves one or two days of back-and-forth. You can also visit flow-meter.com.au for full sensor drawings and order forms.

FAQ: Pitot Tube Duct Flow Sensors

What duct sizes can a multi-port pitot tube flow sensor cover?
Silver Instruments supplies insertion pitot tube sensors for ducts from DN100 to DN2000. For rectangular ducts, the insertion length can be customized from 200 mm to 2000 mm. Tell us the internal dimensions, not the outside dimensions.

How accurate is a pitot tube flow sensor for HVAC air flow?
With proper straight run and temperature compensation, accuracy is plus or minus 1.5 percent of rate. If the duct has only 2 to 3 diameters of straight run, we recommend field calibration. The accuracy also depends on velocity. Below 2 m/s, the differential signal is weak and accuracy decreases.

Can the insertion sensor handle dust or condensation in the duct?
Yes. We use stainless steel sensing tubes with larger impulse holes for dusty air. The static port is positioned to shed condensation. A purge port is optional for heavy dust environments. For standard HVAC clean air, the standard holes are fine.

What output signals does Silver Instruments offer for duct air flow sensors?
We offer 4-20 mA two-wire, 4-20 mA HART, and 0-10 V DC. The HART version is often used for remote configuration. The transmitter can be built into the sensor head or mounted separately. Specify the loop power available at your control panel.

How do I install a multi-port pitot tube in an existing HVAC duct?
You need one round opening, typically 25 mm or 50 mm, and a weld nipple or compression fitting. Insert the sensor to the correct depth. Align the flow arrow with the air direction. Tighten the compression fitting. Connect the impulse tubes to a differential pressure transmitter.

We keep stock of common insertion lengths for DN300 to DN1200 round ducts. Custom lengths ship in 7 working days.

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