When the compressor is running, depending on the size and type of air compressor, the oil will either splash up from the sump into the areas that require lubricating, or there will be an integral pump to pump the oil from the sump up to the parts needing continuous lubrication while the compressor is running. The typical DIY type oil-lubricated home compressor will be the splash lubed variety. If it is splash lubed there will be no extraneous oil pump on the compressor, meaning there is none to maintain or replace. If your compressor is designed to be splash lubed, that process works just fine.