Further objects will be apparent from a consideration of the following description and the accompanying drawings, wherein: Fig. l is a sectional elevation of a pumping system constructed in accordance with the present invention; Fig. 2 is a section on the line 2-2 of Fig. 1; Fig. 3 is a section on the line 3-3 of Fig. l; and Fig. 4 is a schematic view of a modified form of the invention.