How Pitot Tube Flow Measurement Works

In prior posts, we’ve shared many flow measurement technologies, including averaging pitot tube flowmeters.

Katie Hausman Marketing Engineer

Katie Hausman
Marketing Engineer

Emerson’s Katie Hausman shared a new video that the Rosemount measurement brand team has put together that explains how averaging pitot tube technology work. The 3:42 YouTube video, How Averaging Pitot Tubes Work – Rosemount Annubar Technology provides a detailed explanation of how Annubar averaging pitot tubes operate and how this technology can lead to reduced permanent pressure loss compared with other approaches.

The technology is based on differential pressure measurement. Instead of an orifice plate being inserted into the piping where the fluid flow is occurring, a bar from the Rosemount Annubar flowmeter is inserted into the pipe. Mounting styles include insertion, hot tap, and the compact style inserted between raised-face flanges in the piping.

How it operates is that flow moving down the pipe encounters the front side of the T-shaped bar which creates high-pressure above the pipe static pressure, which is picked up by slots in the Annubar sensor. These slots capture the flow profile across the bar to get a more accurate measurement of the flow rate. Low pressure, below the pipe static pressure, is created on the back side of the bar. The differential pressure (DP) transmitter reads these pressure values.

The video highlights some unique aspects of the T-shaped bar which provides greater accuracy over a wide range of flows and reduced pressure drop saving energy. Installation is simplified over conventional DP flow measurement with orifice plates, impulse piping and a DP transmitter. Also, multivariable measurements are available for static pressure, DP, and temperature for mass and energy flow measurement.

Applications for Annubar technology include steam, gas, and liquid flow measurements.

You can connect and interact with other flow measurement experts in the Flow instrumentation track of the Emerson Exchange 365 community.

6 comments

  1. frank kulakowski says:

    Can you tell me what the permanent pressure loss of an averaging pitot tube is? I have one designed for 79″ differential H2O full scale hydrogen gas flow – what would the approximate permanent pressure loss be? I can’t seem to find this information in the Rosemount literature on pitot tubes. Thanks.

  2. Jim Cahill says:

    Hi Frank, Thanks for your comment and question! I checked with a friend on our DP flow team. We can help run a flow calculation with the Toolkit (http://go.emersonprocess.com/rosemount-toolkitinstall-en) program. Our DP Flow specialists would need a little more information to run the calculations for you. If you’re OK with it, I can pass along your email to the team.

    The other option is doing the flow calculations by hand which is admittedly a higher degree of difficulty. The reference manuals to look at are http://www2.emersonprocess.com/siteadmincenter/pm%20rosemount%20documents/00809-0100-1191.pdf and http://www2.emersonprocess.com/siteadmincenter/pm%20rosemount%20documents/00821-0100-4809.pdf

    If you want to go the first path, give me the OK and I’ll pass along your email to our DP flow specialists and ask them to connect with you.

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