Often, the multi-port averaging Pitot tube is an appropriate and economic choice as the primary element for measuring liquids, gases or steam. This widely used flow-sensing device is an adaptation of the instrument invented by the French physicist Henri Pitot in 1732.
As an insertion-type flow meter, it is quickly and easily installed through a small hole drilled into a pipe or duct. As a mechanical device without electronics or moving parts, it doesn’t suffer from electronic drift or physical wear, making it a dependable, repeatable primary element requiring no periodic recalibration. Maintenance may be as simple as inspect and replace as needed.
PMI’s averaging Pitot tubes are available for horizontal and vertical pipes and ducts in sizes ranging from 1/2-in. up to 72-in. diameter or more. In contrast, in-line flow meters often are unavailable or significantly more costly in larger diameters. Moreover, insertion-type flow meters frequently have lower unrecoverable pressure losses than in-line meters and create minimal obstruction of the flow area. Wet-tap insertion meters are available for instances where it is impossible to shut down the process for installation or maintenance.
Units are offered in a wide variety of materials. Probes and heads commonly come in stainless steel and other steel alloys, polyvinyl chloride, brass and copper. As with any process hardware, material selection should take into account the nature of the fluid and operating conditions.
Averaging Pitot tubes are most suitable for flow measurements of clean liquids, gases or steam.
The devices are not the best choice, however, for applications such as liquids with high viscosity, gases with low velocity, or where harmonic vibrations in the probe cannot be avoided. Also, multiphase fluids, such as a gas with significant amounts of entrained liquid or a liquid with entrained gas are not good applications for this technology. Finally, dirty gas or liquid flows can be problematic with the sensing ports on the averaging Pitot tubes. Purging systems can be used to reduce or eliminate blockage in some of these applications.
