Due to the pumping principle and the simple design, liquid ring vacuum pumps are particularly suited to pumping gases and vapors which may also contain small amounts of liquid. Air, saturated with water vapors or other gases containing condensable constituents, may be pumped without problems. By design, liquid ring pumps are insensitive to any contamination which may be present in the gas flow. The attainable intake pressures are in the region between atmospheric pressure and the vapor pressure of the operating liquid used. For water at 15 °C it is possible to attain an operating pressure of 33 mbar. A typical application of water ring vacuum pumps is
venting of steam turbines in power plants. Liquid ring vacuum pumps (Fig. 2.3) are rotary displacement pumps which require an operating liquid which rotates during operation to pump the gas. The blade wheel is arranged eccentrically in a cylindrical casing. When not in operation,
approximately half of the pump is filled with the operating fluid. In the axial direction the cells formed by the blade wheel are limited and sealed off by “control discs”. These control discs are equipped with suction and ejection slots which lead to the corresponding ports of the pump. After
having switched on such a pump the blade wheel runs eccentrically within the casing; thus a concentrically rotating liquid ring is created which at the narrowest point fully fills the space between the casing and the blade wheel and which retracts from the chambers as the rotation continues. The gas is sucked in as the chambers empty and compression is obtained by
subsequent filling. The limits for the intake or discharge process are set by the geometry of the openings in the control discs.
In addition to the task of compression, the operating fluid fulfills three further important tasks:
- Removal of the heat produced by the compression process.
- Uptake of liquids and vapors (condensate).
- Providing the seal between the blade wheel and the casing.
Fig. 2.3 Liquid ring vacuum pump, schematic (Siemens)