Abstract: A hydraulic apparatus for generating impacts comprising primary members having striking and control apparatus which is made up of a plunger which moves reciprocatingly, for striking a tool, inside a housing having an intermediate working zone which has a single inner diameter. An intermediate part making up a piston of the plunger fits therein and has a corresponding single diameter. There is no flow of fluid between these two members and the movement of the plunger is controlled by secondary members and tertiary members which are located in respective housings which make up several chambers, and in which the corresponding plungers are reciprocatingly movable. The apparatus further includes means for discharging the fluid under pressure from within the apparatus for stopping its operation when the tool is not at rest on a workpiece so that the main plunger descends inside the housing to a point below its normal lower operating position.