I think you will just have to use the manufacturer's curve and performance info. I can tell you that I have experience with liquid ring machines in low-pressure waste gas compression and vacuum service and they are pretty reliable because they can handle the dirty gas and some small amount of liquids, so if you run your suction scrubber over, you won't trash the compressor, at least not immediatley. However they are expensive to repair and typically have low differential pressures. Thanks!
Pete
P. J. (Pete) Chandler, PE
Principal Engineer
Mechanical, Piping, Thermal, Hydraulics
Processes Unlimited International, Inc.
Bakersfield, California USA
pjchandl@prou.com