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Flowmeter selection

When you select a flowmeter for your application, determine if you like to measure a gas or a liquid flow, and what the range of measurement isTo size the right flowmeter did you check if it is the right pressure rating and temperature rating? Are you considering the right units? Do you need to calculate any other factors if your system medium is different than the calibration fluid of the flowmeter? 

Variable area flowmeters (VAF’s) can be calibrated on water or air standard, the flow scale range is calibrated at a certain temperature and media pressure. Custom calibrated VAF’s are calibrated for different fluids other than water or air.

A conversion factor can be used to calculate the actual flow of that fluid when it is calibrated for another fluid as it is used for. Find out more about the flowmeter conversion factor

The VAF’s will perform most consistently in the range from 10% to 100% of the scale. 

Turn down ratio of a flowmeter is the range where in the flow rate is accurate. It is the maximum measurement divided by the minimum measurement. For a 1 to 100 flow scale a 10:1 ratio gives you an accurate flow measurement range from 10 to 100.

On Product Gauge the specific product information including flow curves can be found in the supplier product catalog.

Dos and Don'ts using a flowmeter

  • Install a needle valve after the flowmeter in case of a liquid. You like to avoid bubbles in the flow tube, at de compression gas will flash out of liquid.
  • Install a needle valve before the flowmeter in case of a gas. The needle valve isn’t a restriction after the point of flow measurement, so won’t compress the gas. This way the actual flow of gas will be measured at the outlet pressure of the flowmeter.
  • Be aware of the flow regime in the process line where the flowmeter is installed in. Flow measurement technologies like Differential Pressure measurement, Ultrasonic, Turbine flowmeters and Vortex flowmeters. 
  • Magnetic flowmeters can only be used for conductive fluids, they won’t work for Hydrocarbons, Steam or Gas and nonconductive and viscous liquids.
  • Don’t used a glass flow tube Variable Area flowmeter where vibration or shocks of pressure are present. Use a metal flow tube flowmeter instead.
  • Avoid the installation of a flowmeter close to pressure pulsating equipment like pumps to avoid damage of the regulator internals
  • Avoid the use of flowmeters with rotating or moving parts for dirty fluids.
  • The actual volume flow rate of a gas without knowing the pressure and temperature does not give any information about the quantity (mass)
  • The normal volume flow rate Nm3/h is a calculated, virtual volume flowrate of the measured gas as it would be at 0°C and 1.013 bar abs.

Flow measurement instrument categories