Hydraulic percussion instrument and method of operating same

A reciprocating percussion instrument comprising:

• a housing forming an axially centered chamber having a front end and formed thereat with a pair of adjacent ports;
• a tool projecting from the housing and exposed axially in the chamber;
• a double-acting forming front and back compartments and axially reciprocatable between a rear end position and a front end position at least generally in axial engagement with the piston, the piston having a groove forming a fluid-connection path in the chamber between the ports only in the front end position of the piston;
• a pressure source having a high-pressure side and a low-pressure side;
• a conduit connecting one of the ports to one of the sides of the pressure source;
• control means including a pilot line connected to the other of the ports and a distributor valve connected between the high- and low-pressure sides of the pressure source and the compartments for cyclically alternately pressurizing and depressurizing the compartments and thereby axially reciprocating the piston between its end positions at a frequency dependent on pressure in the pilot line;
• and
• pilot-feed means at least periodically connecting a one of the sides of the source to the pilot line for biasing the pressure of same away from that of the side of the source connected to the conduit.