F04C 18/1075

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 helical teeth {the inner and outer member having a different number of threads and one of the two being made of elastic material, e.g. Moineau type}