Gas and liquid Flow measurement in pipes has a long history and and it started some 300 years ago when an Italian physicist Daniel Bernoulli postulated his famous hydraulics principle and theorem in which the change in differential pressure is in inverse proportion to the flow rate in the pipe. Thus if there is an obstruction in the pipe, the flow rate can be measured by measuring the differential pressure.
It was another Italian, Giovanni Battista Venturi a few decades later, made the first pipe flow measurements using Bernoulli’s principle by creating what is now commonly known as a venturi tube. It was this principle that gave rise to the first reliable process pipeline flow measuring devices that are now still very much in use today. Indeed, this principle holds good for all fluids both compressible gases and ‘incompressible’ liquids and it is upon this principle for example, that wings keep aircraft aloft.
Two famous names and four types of liquid flow meters that are in common usage today. The orifice plate , the nozzle, the Venturi Nozzle and Venturi Tube meters are all based on this famous differential pressure principle. So what is the difference between them and how does one select one from another as they all can be used for both gas and liquids?
Venturi Tube Diagram
The first selection criterion is the particulate criteria. If plate/ restriction nozzle erosion will be an issue, then perhaps the smoother profile change of the venturi nozzle or the venturi tube would be the best selection.
If you have space limitations then the selection criterion would favour an orifice plate flow meter as the shortest followed by the nozzle flow meter and the venturi nozzle and then the longest being the venturi tube meter. If pressure losses are an issue for selection, then the venturi tube has the lowest turbulence and the orifice plate the highest with the others in between. If you are looking for the highest accuracy at the lowest flow, then perhaps you should be thinking of another form of meter such as the electromagnetic flow meter or Coriolis meters.
You can see that the selection process is multi-faceted. Whatever meter one uses however, modern metering comes with industry-standard signal conditioners, transmitters and display units.