a skimmer assembly for use in a well has a shielded float / filter assembly with a hydrophobic / oleophilic filter element , which permits selective passage of lighter than water liquids , such as oil or other hydrocarbons , to the inlet of a pumping assembly . the pumping assembly is provided with two pumps : a lower pump for pumping the lighter than water liquid to the surface of the earth , and an upper pump for pumping water in the well to the surface of the earth . each pump is operated by a common logic valve , to which compressed air is supplied and which regulates the application of compressed air to the upper side of a diaphragm in each pump . the lower side of the diaphragm is forced upwardly by means of a spring arranged within the pumping volume of the pump housing and a backing plate positioned just below the diaphragm . a bias spring between the backing plate and a centrally located inlet valve function to close the valve from the inlet to the pump . the logic valve provides an adjustable pumping cycle and incorporates a poppet valve and a pilot leading to an adjustable metering valve . the skimmer assembly can be left in situ for extended periods of time without deterioration in the pumping operation . because the pump has its controlling logic built - in , there is no need for complicated above ground pump controls .