Description
Class E21B : EARTH OR ROCK DRILLING
Subclass 1/34: Percussion drilling (drives used in the borehole E21B 4/00) with a reciprocating impulse member (E21B 1/02, E21B 1/38 take precedence) the impulse member being a piston driven directly by fluid pressure by air, steam or gas pressure working with pulses the impulse member being a piston of an internal-combustion engine