An axial flow-type pump apparatus with gas seals for separating immiscible flowable materials having different specific gravities and a discharge manifold connected to the fluid pump for drawing off the flowable material having the heavier specific gravity with greatly improved efficiency, and pump and apparatus longevity. The flowable material pump employs a rotatable impeller mechanism having a hollow core and a decreasing axial pitch in the direction of materials flow. The flowable materials are introduced into the inlet end of the rotatable impeller to produce a high velocity swirling action and a low pressure area along the longitudinal axis of the flow line, to generate a high centrifugal force as the flowable materials move axially and cause the flowable material having the heavier specific gravity to migrate to the perimeter while the lower specific gravity materials migrate to the center of the perimeter, whereupon they are separately discharged.