with coaxially-mounted members having continuously-changing circumferential spacing between them

Rotary-piston machines or pumps > 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 > with coaxially-mounted members having continuously-changing circumferential spacing between them

Rotary-piston machines or pumps (with non-parallel axes of co-operating members F04C3/00; with the working-chamber walls at least partly resiliently deformable F04C5/00; with fluid ring or the like F04C7/00; rotary-piston pumps specially adapted for elastic fluids F04C18/00; rotary-piston machines or pumps in which the working-fluid is exclusively displaced by, or exclusively displaces, 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 > with coaxially-mounted members having continuously-changing circumferential spacing between them