Abstract: In accordance with the present invention, a pumping unit (10) is disclosed. The pumping unit includes shell structures (20, 22) each having a diaphragm (32, 38) therein to divide the pumping chamber within the structure into first and second compartments. One-way valves permit material to travel from an inlet source to the first compartment and from the first compartment to an outlet source. Deflection of diaphrams provides the impetus to draw material to the first compartment from the inlet source and drive the material to the outlet source. The motion of the diaphrams is induced by a reciprocating piston assembly (94) within a cylinder (84). The motion acts through intermediate chambers (110, 112) filled with pumping fluid and acting on the opposite side of the diaphrams from the first compartments. This permits isolation of the piston from the material being moved to prevent contamination.