When selecting liquid flow meters it is all too easy to go with the flow, as it were, and specify what you always have done for a given application. You may be missing some great options from the myriad of types available.
First of all, do you want volumetric flow or mass flow measurement? The difference could be quite fundamental to your process or other applications. Most liquid flow meter types are volumetric flow but meters that measure mass flow include coriolis flow meters, vortex meters and ultrasonic meters. This is only important for liquids (that are incompressible) when you cannot predict the composition or there is a gaseous element. It is, self-evident however, crucial for gases.
What liquid are you proposing to measure? Is it an electrically conductive fluid such as a water-based liquids with a conductivity of over 1 Siemens/cm²? If so, you could use the most widely use type, the electromagnetic flowmeter or magmeter as it is sometimes known. If the flow contains gas bubbles and you can’t eliminate them by pipework design, then this option would not be appropriate Then, an ultrasonic flow meter or coriolis flow meter may be indicated.
If you want a low cost process flow meter, you could use one of the many differential pressure flow meters. The choice is quite massive and each have their pros and cons. Nearly all meters are now available for use with process industry-standard fieldbus signal conditioners and transmitters. Meters in this class include orifice plate in it’s many variants, venturi meter amd its shorter version, the Dall Tube meter, pitot tube meter or even using a calbrated pipe bend. All of these rely on the Bernoulli Principle where pressure upstream of the device is compared with the flow downstream. All involve press loss and this varies as to type.
If you really just want a flow indicator, you could go for the variable area meter also known as the Rotameter or rising ball meter.
This is a massive subject and we will return to it next time.
Hasta Mañana