Description
Class E21B : EARTH OR ROCK DRILLING
Subclass 1/18: Percussion drilling (drives used in the borehole E21B 4/00) with a reciprocating impulse member (E21B 1/02, E21B 1/38 take precedence) driven by a rotating mechanism with spring-mounted reciprocating masses, e.g. with air cushion with elastic joining of the drive to the push-rod by double buffer springs