Abstract: A positive displacement pump includes a vertical pump cylinder or body formed from an extruded tube or pipe of rigid plastics material, and the pump body has a lower end portion connected by an annular compression coupling and a set of bolts to a mating portion of a pump base supported by a fabricated tubular frame. The pump base includes a smaller horizontal conduit having opposite ends removably connected to a set of flapper-type check valves. The upper end portion of the pump body is connected to a support flange by a set of tie rods extending from the coupling and pump base, and a piston is moved axially within the pump body by an offset connecting rod and an eccentric drive mounted on the output shaft of a motor-reducer drive unit. The drive unit is mounted on a platform which rests on the support flange and is pivotally supported by the frame.