Percussion tool

A percussion tool comprising a housing defining a chamber within which is reciprocally mounted a piston, first and second pressure ducts in fluid communication with said chamber at respective first and second sides thereof, a return duct in fluid communication with said chamber at a point intermediate the points of entry of said first and second pressure ducts relative to said chamber, an inlet duct for delivering a pressurized fluid to said pressure ducts, movable valve means for alternately placing said inlet and pressure ducts in fluid communication in a first position of said valve means for moving said piston in a first direction and placing said first pressure and return ducts in fluid communication in a second position of said valve means while at the same time maintaining fluid communication between said inlet and second pressure ducts and closing communication between said inlet and first pressure ducts for moving said piston in a second direction opposite said first direction, said piston being thereby movable between axially opposite and terminal first and second positions, said valve means being mounted for reciprocal motion in a bore, said first and second pressure ducts opening into said bore, said return duct opens into said bore between the points of entry of said first and second pressure ducts relative to said bore, control duct means opening into said bore at a point of entry between the points of entry of said return and second pressure ducts and having at least two branch duct means opening into said chamber at points spaced from each other in the direction of piston reciprocation, a first of said branch duct means being placed in fluid communication with said return duct through said chamber when said piston is in said first position, and a second of said branch duct means being placed in fluid communication with said second pressure duct when said piston is in said second position.