What to Consider When Selecting a Flow Meter

This article discusses the points that need to be considered in the selection of a flow meter.

Consider Why You Might Need a Flow Meter

Monitoring the fluid flow through a pipe or vessel in real time and controlling the total throughput volume are some of the common applications of a flow meter. With a container to make the liquid to flow into, a stopwatch and a set of scales, one can perform a simple, one-off test with the desired accuracy.

Likewise, it is possible to estimate the flow rate using a simple float in a tapered tube. However, constant local observation is required for this approach. Hiring flow meters is a cost-effective option for short term monitoring applications. Once programmed, flow meters provide users with an accurate, configurable solution to monitor, record and control processes with minimal attention.

Consider the Total Life Cost of the Installation

Initial purchase price is only one element of the operating cost of a flow meter. Although the purchase price and the installation cost of a simple turbine are very low, the actual costs may need to be taken into account over several years of operation. The cost associated with the production downtime due to re-calibration of the simple turbine needs to be considered.

Although the initial purchase price is high, a non-intrusive solid state flow meter is a cost-effective option in the long term. Incorporating an inexpensive flow meter is recommended if the design life of a consumer product is only a few thousand hours. It should be noted that the selection of an appropriate flow meter is an aspect of the overall project design and costing.

Consider the Operating Parameters

One must consider the operating parameters such as temperature, line pressure, flow rate, user-friendliness, type of fluids, and accuracy requirement in the selection of a flow meter (Figure 1). Furthermore, the fluid behavior under all anticipated conditions must be known.

Operating parameters need to be considered in the selection of a flow meter

Figure 1. Operating parameters need to be considered in the selection of a flow meter

Consider the Chemical Compatibility

Users must consider the chemical compatibility of the fluids to be measured with all of the flow meter materials. The typical components of a flow meter include an O-ring, bearings, gears, embedded ceramic magnets, turbine or Pelton wheel, and a rotor. All these materials need to be checked separately against a reliable chemical compatibility table. In addition, users must check their selection with producer of the fluid to be measured to ensure longevity.

Consider All System Parameters

User must also consider the operating conditions of the system wherein the flow meter is intended to be used (Figure 2):

  • Will there be hydraulic shocks?
  • Is the temperature stable?
  • Can the flow exceed the design rate?
  • Does the process require air blown through the system?
  • Is the line cleaned in place?
  • Whether a lower or higher flow range is required in case of a process change and could this be addressed with a single wide ranging meter?

Consider all system parameters in the selection of a flow meter

Figure 2. Consider all system parameters in the selection of a flow meter

Understanding and considering the possible extremes of overall system parameters could avoid much problems and associated expenses later.

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Go Online and Review Available Information

Reviewing available information about flow meters will help selecting the proper flow meter. Most of the information available on the web is useful, although some misinformation is available. Users are advised to check published reports, manufacturer’s sites, and what other people in the industry have done to address their requirements.

Contact Several Possible Suppliers

Some companies will simply market their flow meters, but some organizations will have discussion and consultation with users to provide an optimal flow meter to meet their project and financial objectives. It is advised to use a reliable supplier with a proven quality system and an internationally recognized, traceable calibration system in order to get a high level of after care service and knowledgeable support.

Compare Technologies Pragmatically

After purchase, several technological solutions will usually be offered to that particular flow metering application. Users must consider each solution carefully. The comparison of proposed technological solutions helps users to match a flow meter to their operating parameters, ease of use, its cost of ownership and the level of support it may need.

Technologies such as electromagnetic, Coriolis, ultrasonic, and thermal flow material are viable options to measure a bespoke fluid at low flow rates. Better accuracy can be obtained with Coriolis but at a higher cost. Electromagnetic may be a suitable solution but is dependent on the conductivity of the fluid. Thermal is characterized by slow response time and poor accuracy. Ultrasonic is an ideal solution in terms of price, user-friendly operation, and performance for most applications, especially applications involving low flow.

The charts shown in Figure 3 present the key features of different types of flow meters, of which a perfect flow meter would be a completely solid filled pentangle. As shown in Figure 3, each flow meter technology has its own strengths and weaknesses. For instance, although the variable area flow meter is competitively priced, it typically has poor performance.

Key features of the most popular types of flow meter

Figure 3. Key features of the most popular types of flow meter

Follow Flowmeter Installation Instructions Carefully

The manufacturer’s installation instructions need to be followed carefully to avoid ‘teething’ troubles and to obtain optimal results. Good instrument practice has to be used with the electrical connections. For instance, in a positive displacement meter installation, manufacturers may suggest installing a dummy section of pipe in place of the flow meter during commissioning. This instruction must be definitely followed. Many potential teething problems can be eliminated if the flow meter is installed carefully.

Some Simple Checks Before Calling Your Supplier Out About a Faulty Meter

Since flow meters are examined and certified before dispatch, it is highly unlikely to become faulty straight out of the box. If users find problems during commissioning, they must check the basics first.

  • Is the power supplied to the meter and the instrument, is it the correct specification and turned on?
  • Is the pump running and are the appropriate valves open?
  • When you started the pump or opened the valves did you increase flow slowly to prevent air flow through damage?
  • Is the instrument set/wired correctly (i.e., input port, pulse type, frequency span, units etc.)?
  • Is the flow meter/instrument the optimal one for the installation?
  • Where possible check the output from the flow meter with an oscilloscope or other suitable test instrumentation before proceeding
  • Was the line flushed before installing the meter, could debris be in the meter?

This information has been sourced, reviewed and adapted from materials provided by Titan Enterprises Ltd.

For more information on this source, please visit Titan Enterprises Ltd.

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