Hydraulic impact tool

An impact apparatus, comprising in combination:

• a tubular housing with an axial bore;
• a piston reciprocally carried in the bore and having a lower pressure area shoulder and an upper pressure area shoulder which is larger in cross-sectional area than the lower pressure area shoulder, the piston being movable between a lower rest position, an intermediate start position, an upper position, and an impact position;
• a working tool located at a lower end of the bore for contact by the piston;
• a fluid compression chamber at the upper end of the bore to supply energy to drive the piston from the upper position to the impact position;
• a supply port extending through the housing into the bore;
• a signal port spaced axially above the supply port and extending through the housing into the bore;
• a return port spaced axially above the signal port and extending through the housing into the bore;
• a control port spaced axially above the return port and extending through the housing into the bore;
• axially spaced apart lower, intermediate and upper piston rings on the piston between the lower pressure area shoulder and the upper pressure area shoulder;
• the piston rings and ports being positioned such that:
• during the rest position, the lower piston ring and lower pressure area shoulder are below the supply port, the intermediate piston ring is between the supply port and the signal port, and the upper piston ring is between the signal port and return port;
• during the start position, the lower piston ring and lower pressure area shoulder are above the supply port, the intermediate piston ring is between the supply port and the signal port, communicating the signal port with the return port, and the upper piston ring is between the return port and the control port;
• during the upper position, the lower piston ring is above the signal port, communicating the signal port with the supply port, the intermediate piston ring is between the signal port and the return port, and the upper piston ring is between the return port and the control port;
• and
• during the impact position, the piston rings are positioned as during the start position;
• and
• valve means for providing hydraulic fluid supply pressure continuously to the supply port to raise the piston when the lower pressure area shoulder moves above the supply port in the start position, for providing a return conduit continuously to the return port, for providing a return conduit to the control port until the signal port begins receiving supply pressure at the upper position, then for providing supply pressure to the control port to act on the upper pressure area shoulder to drive the piston downward, and for changing the control port back to a return conduit when the signal port changes back to a return conduit in the impact position.