F04C 18/103

Rotary-piston pumps specially adapted for elastic fluids of intermeshing-engagement type, i.e. with engagement of co-operating members similar to that of toothed gearing of internal-axis type with the outer member having more teeth or tooth equivalents, e.g. rollers, than the inner member {with a crescent shaped filler element, located between the inner and outer intermeshing elements}