Full Title

Rotary-piston pumps specially adapted for elastic fluids (with fluid ring or the like F04C19/00; rotary-piston pumps in which the working-fluid is exclusively displaced by one or more reciprocating pistons F04B) > of arcuate-engagement type, i.e. with circular translatory movement of co-operating members, each member having the same number of teeth or tooth-equivalents > of internal-axis type