Pitot Tubes and Annubars – Specifying and Sizing

Vendor technical data are usually used to select a pitot tube or to size and select an annubar.

When specifying an annubar, its structural compatibility (i.e., the maximum allowable differential pressure) must be known. This information, which varies from one design to another, can be found in vendors’ product brochures.

All annubar sensors are subject to resonance vibration. A vibration force perpendicular to the flow stream occurs due to the shedding of alternate vortices. It is important to check the frequency of the shedding against the natural resonance frequency of the sensor. A resonance calculation may be done either by the vendor or by the user, provided the equations and sensor design data are available. In any case, if the calculated differential pressure at maximum flow rate for an application is below 25% of the total maximum differential pressure allowed for the selected sensor, no resonance calculation is required.

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