Percussion machine

A percussion machine comprising:

• a solid housing body forming a cylinder;
• a double-acting piston reciprocatable in said cylinder and forming a striking mass;
• a tool aligned with and receiving impact from said striking mass;
• means for retaining said tool on said body, said retaining means including:
• a casing fixed to said body and forming a further cylinder;
• a further piston surrounding said tool and slidable with said tool and relative thereto in said casing;
• and
• an annular chamber defined within said casing between a face of said further piston turned away from said striking mass and a confronting face of said casing;
• a source of an incompressible fluid under pressure connected to said chamber;
• a check valve between said source and said chamber;
• a reservoir connected to said chamber;
• and
• a pressure-relief valve connected between said chamber and said reservoir, said further cylinder being coaxial with said tool and formed with a portion of large cross-section on a side of said casing turned toward said piston and a portion of small cross-section on a side of said casing turned away from said piston, said face of said casing being disposed between said portions, said further piston being stepped and having large and small cross-section portions respectively slidable in corresponding portions of said further cylinder and separated by said face of said further piston.