Can Rotameters Be Used in Series for Accurate Flow Measurement?

[hellomoto]

Are rotameters stackable? (i.e. can they be used in series)

I have two rotameters in series measuring the flow rate of CO2 gas. They are from different manufacturers and have different scales, but they are both calibrated for use with CO2. The first rotameter is attached to a pressure regulator that is connected to the CO2 tank (putting the meter directly at the source). The second one is downstream (less than 12 inches away from the source).

The flow rate readings are different between the two meters (about 1/2 LPM). However, when I add significant resistance to the flow (reducing the tubing ID by 85% at the outlet of the second meter via connecting a smaller tube), each meter shows significantly different readings. Example: The First meter read ~4 LPM, the second read ~1/2 LPM. Shouldn't the flow rate be the same through both rotameters? (wrong choice of words. not the same but the readings should be very close. The difference in the non-restricted condition was about 1/2 LPM)

 

[Navin A S]

Yes, rotameters can be used in series to measure flow rate, however, the readings should be close to each other if the system is not significantly restricted. This is due to minor differences in the internal components of the rotameter, such as the float and the scale, as well as differences in the calibration of the two meters. When there is significant resistance in the system, the readings will differ more significantly.