An apparatus for maintaining the operation of a geothermal production pump having one or more impellers and a vertical line shaft for driving the impellers, includes a liquid buffer for isolating a discharge column through which pumped geothermal fluid including non-condensable gases flows from a lubrication column through which flows oil for lubricating one or more bearings of the line shaft, the liquid buffer being interposed between the discharge column and an outlet of the lubrication column to prevent infiltration of the non-condensable gases into the lubrication column. The liquid buffer includes an upper oil receiving section facing the lubrication column outlet and a lower securing element related to the upper oil receiving section. A lowermost bearing is a thrust bearing, and a bowl in which the cup structure and the thrust bearing are housed is in fluid communication with a further bowl in which is housed an uppermost impeller.