HOW TO CHOOSE THE RIGHT FLOW METER

How to Choose the Right Flow Meter

Choosing an industrial flow meter can be difficult because similar-looking instruments may use completely different measuring principles and have very different operating limitations.

The right choice is not necessarily the most expensive meter or the instrument with the highest quoted accuracy. It is the meter that can reliably measure the required medium across the real operating range while fitting the pipe, process, installation and control requirements.

This guide provides a practical flowmeter-selection process for engineers, maintenance teams, original equipment manufacturers and purchasing departments.

Start With the Application, Not the Technology

It is tempting to begin by choosing between ultrasonic, turbine, vortex or thermal mass flowmeters.

A better approach is to define the application first.

Record:

  • What is being measured
  • Why it needs to be measured
  • The minimum and maximum flow
  • Normal operating conditions
  • Pipe dimensions
  • Pressure and temperature
  • Required accuracy
  • Installation limitations
  • Required outputs
  • Approval or certification requirements

Once this information is established, unsuitable technologies can be eliminated.

Step 1: Define What You Need to Achieve

The intended purpose affects the level of accuracy, output and functionality required.

Common objectives include:

  • Displaying flow locally
  • Confirming that flow is present
  • Protecting equipment
  • Measuring consumption
  • Detecting leaks
  • Controlling a process
  • Dosing or batching
  • Monitoring pump performance
  • Allocating utility costs
  • Recording data
  • Connecting to a PLC or BMS
  • Testing a fire sprinkler pump

A simple visual indicator may be sufficient for one application, while another may require a traceable electronic instrument with data logging and communications.

Step 2: Identify the Medium

Specify whether the process contains:

  • Clean liquid
  • Dirty liquid
  • Slurry
  • Viscous liquid
  • Corrosive chemical
  • Compressed air
  • Industrial gas
  • Steam
  • Vapour
  • Mixed-phase flow

Also record:

  • Chemical composition
  • Density
  • Viscosity
  • Conductivity
  • Solids content
  • Bubble content
  • Lubricating properties
  • Flammability
  • Toxicity
  • Whether properties vary

The compatibility of every wetted material should be checked.

Step 3: Define Minimum, Normal and Maximum Flow

A meter should perform effectively across the real operating range.

Provide:

  • Minimum expected flow
  • Normal operating flow
  • Maximum continuous flow
  • Short-duration peak flow
  • Zero-flow periods

This allows the required turndown ratio to be assessed.

A meter may be capable of surviving the maximum flow while still being unable to measure the normal or minimum flow accurately.

Step 4: Confirm Pipe and Connection Details

Record:

  • Nominal pipe size
  • Actual internal diameter
  • Outside diameter
  • Wall thickness
  • Pipe material
  • Internal lining
  • Connection type
  • Pressure rating
  • Pipe orientation

Do not rely solely on a nominal diameter. Actual internal dimensions can vary considerably with pipe schedule and lining.

Step 5: Establish Pressure and Temperature Limits

Specify:

  • Normal pressure
  • Maximum working pressure
  • Test pressure
  • Normal temperature
  • Minimum temperature
  • Maximum temperature
  • Ambient conditions

Pressure and temperature can affect:

  • Meter-body selection
  • Seal material
  • Sensor technology
  • Electronics
  • Display location
  • Fluid density
  • Measurement compensation

Step 6: Define Realistic Accuracy Requirements

Accuracy should be matched to the purpose.

Applications such as billing, dosing, compliance or critical process control may demand tighter performance than general monitoring.

Also consider:

  • Repeatability
  • Resolution
  • Long-term stability
  • Response time
  • Calibration uncertainty
  • Installation effects

A highly accurate meter installed incorrectly may produce worse results than a more forgiving technology installed properly.

Step 7: Assess the Installation

Review what is upstream and downstream of the proposed meter.

Look for:

  • Elbows
  • Tees
  • Reducers
  • Expansions
  • Pumps
  • Compressors
  • Control valves
  • Check valves
  • Partially open isolation valves
  • Filters
  • Heat exchangers

These components can create swirl, pulsation or an uneven velocity profile.

Record the available straight-pipe lengths and whether the meter can be repositioned.

Step 8: Decide Whether the Pipe Can Be Cut

Where process shutdown is possible, an inline meter may offer the best permanent solution.

Where shutdown is difficult or contamination must be avoided, a clamp-on ultrasonic flowmeter may allow external measurement without penetrating the pipe.

Clamp-on technology is not suitable for every fluid, pipe or application, so the complete installation must still be assessed.

Step 9: Select the Required Output

Possible outputs and functions include:

  • Local mechanical scale
  • Digital display
  • 4–20 mA
  • Pulse
  • Frequency
  • Relay alarm
  • Modbus
  • Ethernet
  • Data logging
  • Totalisation
  • Batch control
  • Wireless communication

Confirm the receiving equipment and electrical requirements before ordering.

Step 10: Check Approvals and Area Classification

Some applications require specific certification.

Examples include:

  • LPCB sprinkler-system approval
  • FM Approval
  • ATEX hazardous-area certification
  • IECEx certification
  • Hygienic process requirements
  • Drinking-water approvals
  • Marine approvals

An instrument that works technically may still be unacceptable if it does not carry the required approval.

For fire pump testing, use Techniquip’s dedicated LPCB and FM Approved sprinkler flowmeters.

Selecting by Application

Best Flow Meter for Water Surveys

Clamp-on ultrasonic flowmeters are often valuable because they:

  • Fit externally
  • Avoid pressure loss
  • Reduce disruption
  • Can be moved between pipes
  • Support temporary surveys

Suitability depends on pipe condition, material, dimensions, liquid properties and available straight pipe.

Best Flow Meter for Compressed Air

Thermal mass flowmeters are widely used for compressed air consumption measurement.

They offer:

  • Direct mass-flow measurement
  • Good low-flow sensitivity
  • Wide turndown
  • Consumption totalisation
  • Compatibility with energy monitoring

Explore compressed-air flowmeters.

Best Flow Meter for Clean, Low-Viscosity Liquids

A turbine meter may be suitable where the liquid is clean and the operating range is appropriate.

View Techniquip’s turbine liquid flowmeters.

Best Flow Meter for Viscous Oils

Positive-displacement or oval-gear flowmeters are frequently selected for oils and viscous liquids.

Review Techniquip’s oval gear flowmeter.

Best Flow Meter for Simple Local Indication

A rotameter or variable-area flowmeter can provide a direct, visible reading with relatively simple operation.

Best Flow Meter for Steam

A vortex flowmeter may be appropriate for certain steam applications, subject to pressure, temperature, flow range, steam quality and installation.

View Techniquip’s vortex flowmeters.

Best Instrument for Flow Protection

Where the primary requirement is to detect low flow or loss of flow rather than obtain a precise measurement, a flow switch may be the most practical solution.

Questions to Ask a Flowmeter Supplier

Before purchasing, ask:

  • Is the meter suitable for this exact medium?
  • What is the usable flow range?
  • What accuracy can be expected in this installation?
  • How much straight pipe is required?
  • Does the meter create pressure loss?
  • Which materials contact the process?
  • What maintenance is needed?
  • Is calibration available?
  • Can the output connect to our system?
  • Are approvals current and applicable?
  • Can the meter be installed in this orientation?
  • What information is required during commissioning?

Flow Meter Specification Checklist

Send the following information with an enquiry:

Process medium:
[Liquid, gas, steam or vapour]

Chemical composition:
[Include concentration where relevant]

Minimum flow:
[Value and units]

Normal flow:
[Value and units]

Maximum flow:
[Value and units]

Pipe size and material:
[Include actual dimensions where available]

Connection type:
[Flanged, threaded, grooved, sanitary or other]

Operating pressure:
[Normal and maximum]

Operating temperature:
[Normal, minimum and maximum]

Required accuracy:
[State purpose]

Output:
[Display, 4–20 mA, pulse, relay, Modbus or other]

Installation:
[Orientation and nearby fittings]

Approval:
[LPCB, FM, ATEX or other]

Power supply:
[If applicable]

Frequently Asked Questions

How do I calculate the required flowmeter size?

Meter size should be based on the measuring range and acceptable velocity or pressure loss, not automatically matched to the nominal pipe diameter. Some applications require a reduced meter size, while insertion or clamp-on designs may be selected around the existing pipe.

What does turndown ratio mean?

Turndown describes the ratio between the highest and lowest measurable flow within the stated performance range.

Does a larger flow meter provide more capacity?

Potentially, but oversizing can reduce measurement performance at normal and low flows.

Which flow meters have no pressure loss?

Clamp-on ultrasonic meters do not introduce a component into the process. Inline meters vary: some have minimal loss, while others use a restriction or moving element.

Can one meter be used for different liquids?

Possibly, but changes in density, viscosity, conductivity, sound velocity or chemical compatibility may affect suitability and calibration.

Get Help Selecting a Flow Meter

Techniquip supplies industrial flow measurement equipment for liquids, gases, compressed air, steam and specialist approved applications.

Browse all flow meters or send Techniquip the completed application details for product-selection assistance.