Liquid ring vacuum pumps

[jpolise]

Given that the performance curve for a particular vacuum pump is essentially flat, how can one know what the airflow (capacity) is for a given vacuum gauge reading? In this case, there is no air flow instrument that would provide that info. I'm inclined to think that a system curve will have to be developed much like that done for a centrifugal pump. Where a pressure gauge on the pump discharge would be analogous to the gauge on the vacuum pump.

Any comments?

 

[RaRo]

Liquid ring vacuum pumps are essentially volumetric pumps. The capacity changes because of the suction pressure itself.
Use your measured pressure to get the capacity (in Nm3/h for example - which is in effect a mass flow unit).
Your actual volume flow (in Am3/h or effective m3/h) remains the same, as you said the performance curve is flat.
Given the position of your pressure sensor and what could generate air inlets between the sensor and the pump (flanges for example), you may need to compute some additional pressure drop.

If you want to give a flow value to any monitoring station or as a trend, you need to know what are your incondensables then calculate the gas density based on the measured pressure, factor in the pump volume flow and the result will be the mass flow you want.