Abstract: A pump for concrete or other moist flowable material containing aggregate, including a hopper, a pair of alternately stroking pump assemblies below the hopper for forcing concrete via a junction valve into a common output line, and a loading system for alternately charging the two pump assemblies with concrete from the hopper. The loading system includes a conveyor and a pair of generally vertical charging chambers having lower outlet ports communicating with inlet openings in the respective pump assemblies, and upper portions extending into the hopper through the lower hopper wall and terminating upwardly in open tops disposed above the highest possible level of concrete in the hopper.