How to choose the right flow meter?

There are various types of flow meters available in the market, operating on different measurement principles, in response to the growing demand for such instruments in various industries. How to orient yourself in choosing the most suitable flowmeter for a specific application? Let’s look at some important aspects to consider…

A look to the market

Choosing the right flow meter is important to avoid incurring into plant shutdowns, which can lead to serious economic consequences.

In the process of selecting a flow meter it is helpful to have a comprehensive overview of what the market offers.

Volumetric, differential pressure, electromagnetic, vortex, turbine, Coriolis, ultrasonic flow meters…

It is important to understand the operating principle of these devices and their characteristics, bearing in mind that there may not be a single solution that fully satisfies the constraints imposed by each application.

Price

Often the first criterion for selecting a flow meter is its price: this is the first mistake to avoid!

Initial savings could run out quickly if the instrument and its accessories require high installation costs, frequent maintenance or if the measurements are non-repeatable or even worse, incorrect.

Expected results

It is necessary to determine whether the flow rate information should be continuous or totalized, available locally or remotely, to make the consequent assessments on the transmission system, on the frequency of data update and on the desired accuracy and repeatability of the measurement.

Process fluid

Electromagnetic flow meters do not work with hydrocarbons but require the presence of a medium with a minimum conductivity. Many flowmeters are not able to measure gases or multiphase fluids….

It is therefore important to know as good as possible the fluid to be measured: its status (liquid, gas, multi-phase, steam), its properties (viscosity, density and conductivity), temperature and pressure range in which they operate and how these characteristics can vary or interact with each other. To make sure that the instrument measures accurately from the maximum to the minimum flow rate, it’s useful to know the required measurement range.

Other useful information about the fluid is the presence of bubbles and/or any solid particles, the tendency to create deposits or whether it could be abrasive. Another aspect to consider is the possible corrosive nature of the fluid which could cause deterioration of the wetted parts of the sensor.

Installation requirements

The characteristics of the system and the installation requirements of the flow meter must also be well identified.

Some flow meters must be installed with a certain directionality (vertical or horizontal); others require a certain degree of linearity of the flow, i.e. it is necessary to avoid too much turbulence caused for example by elbows and valves in the pipes, keeping the Reynolds number below a certain value: they must therefore be installed downstream and upstream of a section of straight pipe of a certain length. Some flow meters perform poorly with very small pipes, others are unable to measure fluids in larger pipes.

It is also necessary to know if there are magnetic fields or vibrations nearby the installation point, if the electrical or pneumatic power supply is available, if the area is classified for explosion hazard or if there are other special requirements to be respected such as sanitary standards such as 3A, MOCA, EHEDG and FDA.