Annular casing hammer

摘要

A casing hammer for simultaneously driving casing and drilling a water well comprises a housing having an annular pneumatic chamber with an annular piston that drives an annular anvil which seals the lower end of the chamber. The chamber is formed by outer and inner sleeves of which the inner sleeve is fixed to an end cap solely at its rear end and is thus cantilevered from the end cap, being free of connection at its forward end. The forward end of the inner sleeve is stabilized by means of a relatively small clearance between the anvil and the sleeves at the front end of the chamber. The cantilevered connection of the inner sleeve at its rear end provides a smooth and unobstructed bore through which extends a rotating drill string that also extends through casing while the casing is being driven by the annular hammer.