Water jet pumps and steam ejectors

Included in the class of fluid-entrainment pumps are not only pumps that use a fast-streaming vapor as the pump fluid, but also liquid jet pumps. The simplest and cheapest vacuum pumps are water jet pumps. As in a vapor pump (see Fig. 2.46 or 2.51), the liquid stream is first released from a nozzle and then, because of turbulence, mixes with the pumped gas in the mixing chamber. Finally, the movement of the water - gas mixture is slowed down in a Venturi tube. The ultimate total pressure in a container that is pumped by a water jet pump is determined by the vapor pressure of the water and, for example, at a water temperature of 15 °C amounts te about 17 mbar. 

Even in spite of their low investment costs vrater jet pumps and steam ejectors are being replaced in the laboratories more and more by diaphragm pumps because of the environmental problems of using vrater as the pump fluid. Solvent entering the vrater can only be removed again through complex cleaning methods (distillation). 

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