Hand-operated pneumatic impact machine

A pneumatic impact machine comprised by:

• a hollow body forming a cylinder having an exhaust outlet hole located intermediate the axial ends thereof;
• a double acting piston reciprocable within the cylinder, the piston having opposed working faces and having an annular interior distributing space, said distributing space communicating with the respective axial ends of the cylinder through channels extending from the respective working faces of the piston to said annular interior distributing space thereof;
• one piston rod extending from one said working face of said piston and another piston rod extending from the other of said working faces of the piston through sealing means at the respective ends of the cylinder, one of the said piston rods extending through said annular interior space and providing a conduit for the supply of compressed air to said annular interior distributing space, said conduit communicating with said annular interior distributing space through holes formed in said one piston rod at a position substantially intermediate the axial ends of said annular interior distributing space;
• and a change-over valve freely slidable within the annular interior space of the piston between a first position in which one axial end thereof seals and closes the channels through one of said working faces, and a second position in which an opposite axial end thereof seals and closes the channels through the other of said working faces;
• said valve member being comprised of a hollow cylinder having an axial bore which is of a diameter greater than that of said one piston rod to define a clearance forming an inner channel for the passage of compressed air axially within the bore of said valve, said channels in each of the respective working faces of said piston having a combined cross-sectional area in excess of the cross-sectional area of said clearance between the valve bore and said one piston rod.