Abstract: A solids feeder for transporting particulate solids from an elevated solids feed reservoir and introducing the solids upwardly into the bottom of a solids upflow vessel. The feeder includes a horizontally reciprocatable carriage supporting a vertical feed cylinder fitted with a vertically reciprocatable piston. The piston is vertically reciprocated by a hydraulic cylinder suspended from the carriage. The carriage is reciprocated between a first carriage position wherein the feed cylinder is aligned with a feed chute communicating with the feed reservoir and a second carriage position wherein the feed cylinder is aligned with a bottom solids inlet of the upflow vessel. A tram-like suspension system movably supports the carriage from elevated structural rails. Optionally, the structure of the carriage is adapted to controllably vertically yield during the pumping stroke so as to seat the bottom of the piston actuating hydraulic cylinder on a wedge block mounted on the foundation.