DEVICE AND METHOD FOR ROCK- AND CONCRETE MACHINING

The invention concerns a hydraulic, valveless impact mechanism for use in equipment for the machining of at least one of rock and concrete comprising a machine housing (105; 205) with a cylinder bore, a piston (110; 210) mounted such that it moves within this bore arranged to carry out when in operation repetitive reciprocating motion relative to the machine housing and in this way to deliver impact directly or indirectly on a tool connectable to the equipment for machining at least one of rock and concrete, and where the piston includes a driving part (140; 240) that separates a first drive chamber (160; 260) and a second drive chamber (125; 225), with an effective volume that is greater than that of the first drive chamber. The impact mechanism comprises further a starting means arranged such that it creates for a short duration, during an initial pressurisation of the impact mechanism, a connection between the second drive chamber and the first drive chamber, where the said connection can remain during one complete stroke cycle, in order in this way to set the piston into self- oscillation and avoid the piston remaining stationary at an equilibrium position. Furthermore, the invention concerns a rock drill with such an impact mechanism, and a rock drill rig comprising such a rock drill, and further a hydraulic release valve for the start of valveless hydraulic impact mechanisms. The invention concerns in addition to this a starting method for a hydraulic valveless impact mechanism.