Subclass 5/12: Jet pumps, i.e. devices in which fluid flow is induced by pressure drop caused by velocity of another fluid flow (diffusion pumps F04F 9/00; combination of jet pumps with pumps of other than jet type F04B; use of jet pumps for priming or boosting non-positive-displacement pumps F04D) the inducing fluid being liquid displacing liquids, e.g. containing solids, or liquids and elastic fluids of multi-stage type