Ask the Expert – Using Flowmeters with Different Medias

Visi-Float® Acrylic Flowmeter

Question: I am looking to use a flowmeter calibrated for air to monitor CO2 flow.  Are there any concerns or correction factors I need to apply?

Answer: There are no concerns with using a flowmeter calibrated for air flow to monitor CO2 flow.  The same applies for other gases as well, but you cannot use a flowmeter calibrated for gaseous flow to monitor the flow of a liquid.  Furthermore, depending on the specific gas being used, you should always make sure that gas is compatible with the wetted materials of the flowmeter you are using.  In terms of correction factors, a specific gravity correction factor will need to be used when monitoring the flow of other gases with a flowmeter calibrated for air.  The correction factor equation is as follows:

Q2 = Q1 x sqrt (1/S.G.)


Q1 = Observed Flowmeter reading

Q2 = Standard Flow Corrected for Specific Gravity

1 = Specific Gravity of Air or Water

S.G. = Specific Gravity of media being used in flowmeter originally calibrated for air or water.

This equation can be found in the beginning of the Flow section in the Dwyer catalog and on the Dwyer website.

Alternatively, special ranges and scales can be provided; for specific information on custom flowmeters or for additional support, please contact our customer service and technical support departments.

For further information, please see our video entitled, Fix your Flow…Specific Gravity and Pressure Corrections for Variable Area Flowmeters.