Abstract: In a hydraulic rock drill there is a hydraulic so called recoil damper that damps the reflected shock waves that propagates from the rock backwardly through the drill stem. The damper comprises a support piston (68) slidably in a cylinder so that a pressure chamber (20) is formed in which the support piston has a piston area. Narrow clearances (75,76) between the support (68) and its cylinder form leak passages and these leak passages are coupled in series with an orifice restrictor (84) to a sump. The pressure peaks in the pressure chamber do not reach sealing rings located at the outer portions of the clearances.

Abstract: In an hydraulic rock drill there is an hydraulic so called recoil damper that damps the reflected shock waves that propagates from the rock backwardly through the drill stem. The damper comprises a support piston (68) slidably in a cylinder so that a pressure chamber (20) is formed in which the support piston has a piston area. Narrow clearances (75,76) between the support (68) and its cylinder form leak passages and these leak passages are coupled in series with an orifice restrictor (84) to sump. The pressure peaks in the pressure chamber do not reach sealing rings located at the outer portions of the clearances.

Abstract: In a hydraulic rock drill the valve (27) is controlled by two control lines (37, 42), each control line having a plurality of branches with ports (38-41 and 43-46) which open into the hydraulic cylinder of the rock drill.A valving pin (48) is slidable in a bore that intersects all of the branches of both control lines. By axially displacing the pin, the operator can pre-select the stroke length by deactivating some of the control lines and thereby the impact energy per blow. The control lines are deactivated in a predetermined bound relationship to each other.

Abstract: A recoil damping device for a percussion tool in which the recoils are damped by means of a pressurized hydraulic fluid entrapped in the machine housing.