Water cooled vaccum pumps with VFD's

[emericksmaple]

Does anyone out there use a 3 phase motor with VFD to run a liquid ring(water cooled) vaccum pump? I was told that it is not recommended, due to the pump not working correctly at slower speeds?

[DrTimPerkins]

Due to their design, some liquid-ring pumps will not maintain a vacuum at less than 80% their rated speed, so if a VFD is used, it should be programmed to only operate over a narrow range. Therefore a VFD has limited usefulness in those applications.

[emericksmaple]

Thank you for the reply, Dr Perkins.