This sub-class comprises: non-positive-displacement pumps for liquids, for elastic fluids, or for liquids and elastic fluids, whether rotary or not having pure rotation.
Combinations of non-positive-displacement pumps with other pumps are dealt with in sub-class Fulltext... Hierarchy... Expanded...F04B, except that the use of such other pumps for priming or boosting non-positive-displacement pumps is dealt with in the present sub-class.