Which flow meter?

A flow meter can provide an accurate, configurable solution that can monitor, record and be used as a method of control with minimal attention once programmed. But to choose the right device, you need to ask yourself why you need one.

Common applications include monitoring the amount of fluid travelling through a pipe/vessel in real-time, or monitoring and controlling the total throughput volume (totalising).

If a simple, one-off test is all that you need, a container to flow the liquid into, a set of scales and a stopwatch may offer all the accuracy needed.

Similarly, flow rate could be estimated by using a simple float in a tapered tube. If you wish to avoid the inconvenience of constant local observation, some companies hire flow meters and this may offer an economic solution for short-term monitoring applications.

Total life cost

Initial purchase price is only one aspect of the costs of running a flow meter. A simple turbine may be inexpensive to purchase and install, but the true costs may need to be considered over several years of operation.

For instance, how often will your production line have to be down while that simple turbine is being recalibrated? It may be that a nonintrusive solid-state flow meter will be more cost effective in the long term.

However, in situations where a consumer product with a design life of only a few thousand hours requires a flow meter - an inexpensive device would be appropriate.

Operating parameters

Flow-meter selection will, of course, depend on flow rate, line pressure, temperature, accuracy requirement and ease of use. In addition, it is important that you know how your fluid behaves under all anticipated conditions.

Users must also ensure that the fluids to be measured are chemically compatible with all the materials of the flow meter.

This will include its O-ring, a rotor, turbine or Pelton wheel, embedded ceramic magnets, gears, bearings, etc.

Check each material separately against a reputable chemical compatibility table and double check your selection with the manufacturer of the fluid you wish to measure.

System parameters

The selection of the most appropriate flow meter will also depend on the system it is intended to be a part of. Will there be hydraulic shocks? Can the flow exceed the design rate? Is the temperature stable? Does the process require air blown through the system? Is the line cleaned in place?

If there likely to be a change in process which would require a higher or lower flow range, could this be met with a single wide ranging meter now?

Awareness and consideration of the possible extremes of your overall system could save much inconvenience and expense later.

Do your homework

There is a vast amount of information about flow meters on the web. See what other people in your industry sector have done, and take a look at manufacturer’s sites and published reports.

It may be that someone has had similar requirements and solved similar issues to your own.

Compare suppliers and technologies

There are some organisations that will simply sell you a flow meter, and there are others who will discuss your application and consult with you on your project requirements before suggesting a solution that meets both your operational and financial goals.

Where possible use a reputable supplier with a recognised quality system in place and evidence of a high level of after care service and support.

After shopping around, it is likely that you will have been offered several technological solutions.

In comparing proposed solutions, you are aiming to match a flow meter not just to your operating parameters, but also cost of ownership, ease of use and the level of support it requires.

Follow installation instructions

It is important to follow installation instructions carefully to eliminate teething problems and to ensure optimal results.

For example, if you are installing a positive displacement meter, the manufacturer is likely to suggest that a dummy section of pipe is installed in place of the flow meter while the system is commissioned.

It is very important that you do this, because in a new installation, debris can be caught somewhere in the system.

You should also check that all the other components in the system are working correctly, including non-return valves, pumps and isolation valves.

Careful installation can eliminate many potential ‘teething’ troubles.

The author is sure he is not alone in having travelled hundreds of miles only to switch on a power supply of a “faulty” meter which is “not responding to flow”.

If problems occur during commissioning, always check the fundamentals first before calling your supplier.

Is the installation wired correctly? Is any secondary instrumentation compatible and is it configured correctly? Are the cables numbered correctly?

By their nature, flow meters are checked and certified before they are dispatched so it is extremely rare for them to malfunction straight out of the box.