F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
F04C—ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
F04C19/00—Rotary-piston pumps with fluid ring or the like, specially adapted for elastic fluids
F04C19/002—Rotary-piston pumps with fluid ring or the like, specially adapted for elastic fluids with rotating outer members