LIQUID RING PUMPS

A liquid ring vacuum pump is a non-pulsating pump that removes gases by means of a rotating impeller blade entering and leaving a ring of liquid. In operation, the pump casing is partially filled with a sealing medium usually water. As the impeller is rotated, the radial vanes force the sealing fluid to the periphery of the pump casing where it forms a liquid ring around the center void thus creating our pumping 'cylinder' or chamber. The constant rotation of the impeller causes it's vanes to enter and leave the liquid ring and ejecting the sealant from the pockets between the vanes. As the sealant is ejected, it is replaced by the gas being pumped.

U.S. Vacuum Tuthill/Kinney® Beach-Russ

The lower limit of vacuum for a liquid ring vacuum pump is 30 mm Hg (Torr) using water as it's seal fluid. Using other sealing fluids, the limit is approximately 20 Torr above the vapor pressure of the sealing fluid exiting the pump.  Vacuum boosters can be employed to extend the operating vacuum range to about 5mm Hg.

LIQUID RING systems are probably the MOST DIFFICULT type of vacuum pumping system TO ENGINEER, since so many variables are involved in sizing the unit. You have to deal with vapor pressure and temperature limitations of the sealant, condensing rates of the pumped vapor with-in the pump, cavitation, corrosion, elastomer compatibility, process vapor carryover through condensers, sealant options, sealant recovery options and others. Hopefully, the following section on liquid ring systems will help when sizing your units.