These equipment are ejectors where pressurized water is used as motive fluid. The exhausters are particularly suitable when steam supply is not available and in all those cases that vapors with high amount of associated steam have to be handled, because while pumping the gases also work as a condenser.
These equipment allow high compression ratios and reach low suction pressures with just a single step. The suction pressure is limited by the vapor pressure of the motive water. In case of using a non volatile liquid as motive fluid, it can be reached a pressure of few Torr.