Damping device for a percussion rock drilling machine

Device for a percussion rock drilling machine for transferring a feeding force to a drill string (15), said device comprising a damping chamber (23) operatively connected between a feeding force influenced means (11) and the drill string and valve means (41) for controlling the supply of pressure gas from a supply conduit (35) to the damping chamber, the drill string being movable by the gas pressure in the damping chamber when the feeding force is not applied but being balanced by the gas pressure when normal feeding force is applied, said device characterized by valve means operatively associated with said damping chamber for venting the damping chamber (23), said valve means allowing pressurization of the damping chamber at a selectable pressure level after said damping chamber is vented.