In this short podcast episode, Bryan talks about the differences between pitot tubes and static pressure probes. He also explains how each one works.

People often mix up static pressure probes and pitot tubes. A pitot tube is a tube within a tube, and a static pressure probe is just a tube with holes in the side but not at the end. When we measure static pressure, we're measuring the pressure against the duct. (Think of it as balloon pressure rather than air velocity.) We use static pressure probes to look for a differential between a probe and atmospheric pressure or between two probes. As the air travels around a static pressure probe pointing in the correct direction, its velocity force will not act on the probe. We do NOT want to measure velocity with a static pressure probe.

Pitot tubes, however, come in twos. One tube comes off the side (attach a hose to this one), and one comes off the bottom. You can use the side port of the pitot tube to measure static pressure. You also have an end port to measure total pressure, which is static pressure plus velocity pressure. When using a pitot tube, you can get the velocity pressure by subtracting the static pressure from the total pressure.  You point the pitot tube into the airstream to get that measurement. However, pitot tubes will only give you accurate data if you have an accurate manometer and have ideal velocity conditions. Proper positioning and duct traverse techniques are also integral to getting accurate data.

 

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