Air percussion boring machine

An air percussion boring machine comprising:

• percussion means having a hollow cylindrical housing;
• a rear head having air distribution means disposed within said housing;
• a percussion piston located inside said housing for reciprocating under the effect of compressed air and for delivering impacts at the end of the power stroke to a tail piece of the boring tool;
• a front head disposed coaxially with respect to said percussion piston and said tail piece of the boring tool;
• a boring tool holder connected to said front head and having a central hole for permitting said boring tool to extend axially outwardly therefrom;
• a boring tool rotation mechanism, installed in the front portion of the boring machine, having a stator with a plurality of stator blades secured on its internal surface equidistant from each other, a rotor installed inside said stator and provided with a plurality of rotor whose number is equal to that of said stator blades, a sleeve installed inside said rotor, a ratchet installed in said front head and coupled to the tail piece of said boring tool for rotating same, at least one pair of hinged pawls in said sleeve, said pawls of each of said pair of pawls being coupled to each other, and said pawls having a common axle of rotation parallel to the central axis of the boring machine and directed in different senses whereby one of the pawls in each pair is used to rotate said ratchet in one direction whereas the other pawl in each pair is used to rotate said ratchet in an opposite direction;
• means for urging said pawls to said ratchet comprising air power cylinders with pistons contacting said pawls;
• an air pressure source in communication with a first group of air power cylinders designed to rotate said ratchet in one direction when said pawls are in mesh with said ratchet, while a second group of air power cylinders designed to rotate said ratchet in an opposite direction is in communication with the atmosphere;
• and an adapter flange provided between said stator and the front head and being provided with two holes, a first of said holes being in communication with said first group of air power cylinders for rotating the ratchet in one direction via first passages provided in said sleeve, and a second of said holes being in communication with the second group of air power cylinders for rotating the ratchet in the opposite direction via second passages provided in the sleeve, whereby each of said holes of the adaptor flange is in communication either with the air pressure source or with the atmosphere.