Today, multiple methods, technologies, and tools exist to measure flow. Often, this makes the task of selection harder, pushing users towards decisions based on price alone. That doesn't work because so often, the cheapest flowmeters come with high costs of installation and accuracy issues unless they're perfectly suited to your specifications.

We'd like to offer some thoughts on what you might consider in your decision to get a flowmeter.

1. Assess The Need

Do you just want to know the rate at which your liquid is moving through a pipeline or do you need to be able to control the flow to minute fractions? The answer to that question will determine if you need flowmeter or a relatively simple flow indicator instead (perhaps one that lends itself to being calibrated to scale up to something more sophisticated). Flow indicators will cost you a fraction of what a flowmeter would. Knowing the complexity of your operations and starting by deciding if you need the equipment at all, while it sounds elementary, is an expensive step that is frequently missed.

2. Understand Your Requirement

Different fluids (and gasses) behave differently while flowing through their pipelines. Viscosity, or how the fluid resists flow, is the primary factor that affects flow. Thorough knowledge of the properties of the material you need to measure is vital. Is the liquid Newtonian or non-Newtonian? How do extreme temperatures and pressure affect it? These answers will help you make the first cut and narrow down the options open to you. Now calculate the liquid's Reynolds number⁽¹⁾ and check against your top contender flowmeters' Reynolds range. This will accurately help you choose one that is suited to the application at hand.

There are a few common types of flowmeters.⁽²⁾

• Orifice plate meters are the most popular choice in the case of single-phase, consistently moving liquids.

• Positive displacement meters are a good option for the lowest uncertainty of measurement.

• Electromagnetic meters measure the widest flow range.

• Turbine meters are best for the highest short-term repeatability.

• Coriolis mass flowmeters are best used when measuring extremely viscous liquids.

3. Installation matters

Once you're close to a decision on a particular flowmeter, think about where it will be installed. Ideally, it needs to go where there are few (if any) obstructions like bends and valves since these can affect the accuracy of your readings. Get a clear understanding of the installation process that your manufacturer recommends. Make the complexity of installation one of the points on the basis of which you choose a flowmeter.

(1) http://www.engineeringtoolbox.com/reynolds-number-d_237.html
(2) http://www.chemicalprocessing.com/articles/2016/pick-the-proper-flow-meter/?show=all