flow meters and controllers are intended for use in low-pressure applications. This is because an accurate measurement of the volumetric flow rate by means of differential pressure requires the flow at the differential pressure sensor to be in a laminar state. The state of the flow is quantified by what is known as the Reynolds Number. If the Reynolds Number gets above a certain quantifiable point the flow will become non-laminar. Most volumetric flow devices are sized to make valid full-scale measurements with line pressures up to 10 – 15PSIG when using air.
As a general rule, if your line pressures will be above 15PSIG, mass flow device will be more appropriate due to the additional sensors required to compensate for the increased densities.