2 replies to this topic

[curious_cat]

While buying a liquid service rotameter is it typical to stay below the manufacturer's Viscosity Immunity Limit and then only adjust flow calibration by a ratio of densities versus water? 

 

Or do others actually insist on doing a calibration with the actual design fluid ever? 

 

Is there a more sophisticated formula than a density ratio for going from the calibration fluid to the service fluid? Most vendors seem to operate their calibration rigs with water. 

 

My duty is low viscosity liquids ( <3 cP) and flows are fairly low (~1000 Litres / hr)

[fseipel]

If the viscosity is < 3 cP, you should be able to find a rotameter with a sufficiently high immunity ceiling.  The ribbed floats have a higher ceiling than, say, a spherical float.  I've never seen a formula that includes a correction for anything but density/temperature.  This is probably because the viscosity effect depends on the float geometry, whereas the density correction just depends on float and fluid densities only and so is independent of float shape.  In recent years I've used magnetically coupled rotameters; the advantage being no glass that can break, and the ability to add an optional transmitter capability to record/totalize flow, as well as extremely high pressure ratings.  If you're changing media frequently, having a meter with an external metal scale bar adjacent to it, rather than scale inscribed on tapered meter tube, may be preferred since you can change it out or include multiple scales adjacent to one another.

[curious_cat]

Good points @fseipel! Thanks. 

 

I especially like the external scale idea. Yes, changes are indeed frequent.