Difference Between Rotameter and Flow Meter Readings for Compressed Air

Hey all, I recently ordered one of ATO's digital flow meters (SKU: ATO-FLOW-MF5700) to measure compressed air flow rates through our assemblies. We’ve been using Dwyer Rotameters, but I wanted to compare their readings with the new digital meter, so I put them in line with each other and ran some tests. The problem is, that I’m seeing very different results between the two devices. Has anyone experienced this, or know what could be causing the difference?

It could be related to how each meter calculates flow. Rotameters typically measure flow based on the working pressure of the system. If your pipeline has high pressure, the Rotameter's reading will reflect the compressed state of the gas. A digital flow meter like the one from ATO might measure flow under standard conditions (20°C at 101.325 kPa), which could explain the discrepancy. What's your working pressure?

Ah, that makes sense! I didn’t think about the pressure difference. Our pipeline is running at 80 psi. Does that mean I should apply some sort of correction factor to the Rotameter readings to match the digital meter?

Ah, that makes sense! I didn’t think about the pressure difference. Our pipeline is running at 80 psi. Does that mean I should apply some sort of correction factor to the Rotameter readings to match the digital meter?
Yes, exactly. With the pipeline running at 80 psi, you’re looking at a significant difference in flow rate because of how the gas is compressed. You’ll need to adjust the Rotameter readings to account for this. There’s usually a correction factor you can apply to bring the readings in line with standard conditions. If your digital flow meter is calibrated for standard conditions (like 20°C and 101.325 kPa), that’s probably why you’re seeing such a big gap between the two.

Thanks, everyone! All of your clarification helped. Turns out I needed to apply a correction factor for the Rotameter since our system is under 80 psi. Once I did that, the readings from both meters aligned perfectly. Thanks again for the help—this community is awesome!