Reverse flushing drill pipe - with air passage valve actuated by hydrostatic drilling fluid pressure

摘要

A string of double-walled drill pipes for use in the reversed flushing has an annulus between inner and outer pipe for the supply of compressed air and the inner cross-section for the rising mixt. of drilling mud and air. An air passage valve to connect the annulus with the inner cross-section is spring loaded and responds to the hydrostatic pressure of the fluid between the drill pipes and the borehole wall. This makes it possible to inject air into the central cross-section at the desired depth up to the maximum injection pressure without having to raise the string of pipes.