## What is a flow meter and how does it work?

Flow gauge, flow indicator, liquid meter, flow meter – they’re all the same thing; depending on the industry they may have different names, but their function remains the same: to measure flow.

In the simplest of terms, a flow meter is a device which is used to measure the quantity and/or flow rate of a gas or liquid as it moves through a pipe. Some flow meters measure the amount of fluid that passes through the pipe in a given time, while others measure the total amount of fluid or gas that has passed through the flow meter. Sign up for FlowSight, the Litre Meter newsletter.

How do flow meters work?

Flow meters consist of three parts: a primary device, a transducer, and a transmitter. As the fluid passes through the primary device, the transducer senses it; the raw signal from the transducer is then sent to the transmitter and turned into a usable flow signal.

Mathematically speaking, a flow meter typically uses the following equations:

• Q = A · v – Where the volume of fluid passing through a flow meter is equal to the cross-sectional area of the pipe (A) multiplied by the average velocity of the fluid (v).
• W = r · Q – Where the mass flow of fluid passing through a flow meter (A) is equal to the fluid density (r) multiplied by the volume of the fluid (Q).

Different types of flow meter

There are a number of different types of flow meter available, each one suited to a different purpose, but always with the same goal of measuring the flow of a fluid or gas through a pipe.

• Positive displacement flow meters: As the only meters to measure the actual volume, positive displacement meters work by repeatedly filling and discharging fluids from a chamber. Also known as volumetric flow meters, or rotary piston meters due to the way in which they operate.

• Inferential flow meters: These types of meters don’t measure volume, mass, or velocity. Instead they measure the flow of a fluid by inferring its value from other measured parameters such as differential pressure.
• Velocity flow meters: The flow of fluid through the pipe is measured by the velocity of the flowing stream in order to determine the volume of the flow.
• Mass flow meters: A mass flow meter, also known as an inertial flow meter, measures the flow rate of the mass of fluid as it travels past a fixed point during a specified unit of time.

What type of flow meter do I need?

There is no one-size-fits-all solution when it comes to flow meters. It largely depends on the industry you’re in, and what the flow meter will be used for. Here at Litre Meter we’re the flow meter experts, so we can help you to choose which type will work best for your needs, but here are a few questions to ask yourself before looking into purchasing a flow meter for your company:

• What gas or liquid do I want to measure?
• What level of accuracy do I require?
• What is the temperature and viscosity of the fluid?
• Does the fluid flow continuously or intermittently?
• Will the meter be mounted in a safe or hazardous location?
• What are the minimum and maximum flow rates?
• What is the maximum pressure at the location?
• What level of pressure drop is allowable?
• Is the fluid compatible with the materials used in the flow meter?

Each type of flow meter has a different set of applications and constraints, so the best way to choose the right one is to use the application of the equipment, rather than the technology, to guide you in your choice. Once you know the answers to some or all of these questions speak to us and we can help you to determine which flow meter will best suit your needs.

## Top tips for selecting the right flowmeter for you

At Litre Meter, we want to make sure that you get the most for your money when it comes to buying a flowmeter, so we’ve put together our top tips for selecting the right device for you…

Made to quantify the rate that liquid or gas moves through it, flowmeters are required by test and measurement professionals to provide results in a wide variety of applications where accuracy is critical. This includes measurements for familiar household things like heating, ventilating and air conditioning to aerospace and agriculture.

Type of flowmeter

There are different types of flowmeter to suit different purposes and applications. By simply profiling the gas or liquid it is measuring, it’s possible to discover how it behaves when flowing through a pipe. You can then narrow down the choice of device to best cope with the conditions of the application. If you’re unsure about how to do this, get in touch with a professional and they’ll be able to help.

Purpose

There are a number of different uses for flowmeters, and as we’ve just mentioned, whatever you intend to use it for will affect your range of choice. You must consider temperatures needed, the turndown ratio, whether or not it has to be user-friendly for the workplace, and the type of liquid or gas that it is measuring the rate of. For example, if fluid containing traces of silt or sediment is flowing through the pipeline, we’d suggest that you use an ultrasonic Doppler flowmeter.

Chemical compatibility

It’s really important to take into account the materials involved in the process you intend to carry out with the flowmeter. Some materials are not compatible and this can have an effect on both the fluid or gas quality and the flowmeter’s durability. Check each material separately against a reputable chemical compatibility table, and checking your selection with the manufacturer of the fluid is also a wise idea to avoid any potential problems or issues.

Price

Whilst buying a cheaper device may tempt you by saving you money initially, it could actually end up costing you more in the long run. Don’t let short-term savings sway you and think about it practically; a higher priced flowmeter can be more cost-effective in its quality, its back-up and its durability.

Longevity

Talking of durability, before purchasing the device, you should find out how long it typically lasts. Ask the supplier about its failure rate or the type of application you need it for. This may have an impact on the price, but by evaluating the total life cost of it, you will most likely find it to be worthwhile.

Installation

It’s also important to think of the installation before selecting your flowmeter. Consider exactly where and how it will be installed as this can hugely affect its accuracy and efficiency. You must think about the type of meter and whether it’s affected by any obstructions in the pipeline like joints, bends or valves as these could cause distortions to the flow.  This is all worth doing because if the device is installed correctly in a suitable application, it will be more accurate and will ultimately save you money.

If you need help in selecting the best flow meter for the job, our Litre Meter team will be happy to help. Simply get in touch via our Contact Form or give us a call on 01296 670200.

## Here’s some pointers to finding the right flowmeter for your application

1. Know your flow rate/ flow range. Perhaps this is obvious but you need an idea about what your flow rate might be to size the meter correctly. Not only the maximum and minimum but also the normal flow rate expected. Maybe there will be a unique flow rate at start up?

Read moreTen top tips for flowmeter selection:

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