In industrial applications, pitot tubes are used to measure air flow in pipes, ducts, and stacks, and liquid flow in pipes, weirs, and open channels. Pitot tubes are generally used for flow measurements of secondary importance, where cost is a major concern, and/or when the pipe or duct diameter is large (up to 72 inches or more). The main difference between an orifice and a pitot tube is that an orifice measures the full flow stream while the pitot tube detects the flow velocity at only one point in the flow stream. It consists of a tube with a small opening at the end, facing the oncoming flow stream. The velocity of the fluid at the opening of the tube decreases to zero (Stagnation point). Pitot tubes are recommended only for highly turbulent flows (Reynolds Numbers > 20,000) where the velocity profile tends to be flat enough so that the insertion depth is not critical.

An averaging pitot tube is provided with multiple impact and static pressure ports and is designed to extend across the entire diameter of the pipe. The Annubar probe senses a total pressure (impact and static pressure) through the upstream slots and a low pressure through the downstream ports. The impact pressure and the downstream low pressure are affected by the alignment of the sensing slots/ports. The upstream ports are blocked from the downstream ports by a barrier in the tube. There is no flow through the tube, only flowing forces are applied to it, developing upstream and downstream pressures. Pitot tubes can be installed in threaded fittings, welded, flanged.

A deviation from perpendicular to the axis of the pipe in any direction will affect either or both of the sensed pressures (Changes within the 3° limits will have insignificant effects). For accurate measurement, the design of the Annubar probe requires that the flow sensing slots/ports be located at specific points in the flow stream. The averaging functions of the Annubar primary element will not take place if the flow profile is not symmetrical. The flow profile can be influenced by any upstream device which disturbs the flow, like valves, elbows, diameter changes, etc. Sufficient length of straight run pipe upstream of the Annubar primary element will allow the turbulent flow profile to develop. A flow straightener or straightening vanes may be used to reduce the length of straight run required.

Values in the above table expressed as multiples of internal diameter.
Values used, are common used values, manufacturer shall specify the upstream and downstream length.