DIFF Subgroup
E21B 37/045 Full Title
Methods or apparatus for cleaning boreholes or wells (E21B21/00 takes precedence) > Scrapers specially adapted therefor > operated by fluid pressure, e.g. free-piston scrapers
E21B 37/045 Methods or apparatus for cleaning boreholes or wells (E21B21/00 takes precedence) > Scrapers specially adapted therefor > operated by fluid pressure, e.g. free-piston scrapers