Any time a flowing material is disturbed by an obstruction (formally known as a bluff body), the flow begins to oscillate. This occurs in both gasses and liquids; one of the most common examples of this effect is the way that wind creates a whistling sound when it blows through tree branches. The same force causes flags to wave on windy days.

One factor that's common to these examples is that these oscillations only last as long as the flow does. When the wind drops, the breeze stops whistling and the flag stops waving. When the material in flow hits an obstruction - like the tree branches or the flag pole in our examples - it separates and moves around the object. On either side of the obstruction (called a bluff body or shedder), vortex swirls spring up at the points where the flow hits the object. These swirls alternate from one side to the other, and one side is typically lower in pressure than the other. Each of the swirls has a distinct frequency which is proportional to the speed with which the material is flowing. The frequencies on either side of the bluff body are out of phase to each other by 180 degrees. The relationships between these forces are consistent enough that measuring the vortex frequency around a bluff body enables one to make an accurate calculation of flow rate. In other words, fluid velocity is proportional to both the width of the bluff body and the frequency of the vortices it creates.

This is the operating principle used by the vortex flow meter. It can be used to accurately measure the speed of gasses, steam, and clean liquids (i.e. those which do not contain suspended solids). Flow meters used with low-density gasses need to be especially sensitive in order to detect the very small pressure differentials created in such conditions. Vortex meters are particularly common in applications where steam flow needs to be measured, and they offer significant advantages over other measuring tools. They have no moving parts, they are economical, they have minimal maintenance requirements, and they're extremely durable.

Vortex meters are also notable because they're one of the few devices that is equally effective with fluids in any phase (i.e. gas, liquid, or vapor). Vortex metering is the go-to technology for reliable, low-cost, low-maintenance flow measurement in a host of different applications. Because of its great flexibility, the vortex flow meter is particularly useful for measuring gasses which are wet and/or dirty. Because these meters are free of moving parts, they require minimal maintenance or cleaning.
SmartMeasurementTM ‘s ALVT family of vortex flow meters including wafer, flanged and insertion types will cover any vortex applications in the process industries.  Moreover the ALVTmass produced by SmartMeasurementTM can take direct mass flow readings on steam or gas flow applications with built-in temperature and pressure sensors well as mass flow transmitter.