Patent ID: 8800425

Claim:
A percussion device comprising a body and therein a percussion piston that moves along a longitudinal axis in a reciprocating manner by action of pressure fluid, wherein the body includes a first and a second pressure fluid space located toward a front end and toward a rear end of the percussion piston, respectively, each pressure fluid space formed at least in part by a portion of a surface of the percussion piston, a control valve that is substantially sleeve-like, located in the second pressure fluid space and movably mounted in a direction of the longitudinal axis of the percussion piston, and a plurality of pressure fluid channels for moving pressurized pressure fluid in and out of the pressure fluid spaces of the percussion device, wherein toward the rear end of the percussion piston there is a radially protruding annular surface facing the control valve and on the inner surface of the control valve there is a radially protruding annular surface facing the percussion piston so that as the respective radially protruding annular surfaces are aligned they substantially throttle the pressure fluid flow between a first side and a second side of the aligned annular surfaces, the percussion device configured for the radially protruding annular surface of the piston to shift rearward and forward of the radially protruding annular surface of the control valve, wherein, as a reverse stroke of the percussion piston starts, the control valve is in a rearmost position and closes access of the pressure fluid to the second pressure fluid space from a first of the pressure fluid channels and opens access to a second of the pressure fluid channels, and wherein, the percussion piston having shifted rearwardly to a predetermined position, the radially protruding annular surface of the percussion piston will be in alignment with the radially protruding annular surface on the inner surface of the control valve, and consequently as the reverse stroke of the percussion piston continues, the pressure in the second pressure fluid space rises decelerating the reverse stroke of the percussion piston and at the same time pressure is acting on the surfaces of the control valve on the side of the second pressure fluid space to move the control valve towards the front end of the percussion device, whereby the radially protruding annular surfaces of the percussion piston and of the control valve will move apart and reduce the throttling of the pressure fluid flow between the first side and the second side of the annular surfaces and whereby the control valve closes access of the pressure fluid to the second of the pressure fluid channels and opens access of the pressure fluid to the second pressure fluid space from the first of the pressure fluid channels.