A drilling apparatus 1 having a twin-impact system can work continuously with a shank end 5 is provided with a compensation ring 10 on the rotary impact side, which has a material with hardness that is lower than that of the material of the pipe and striker 8 and/or corresponding to the adjacent end portion 11 of the shank end 5 and has a shape and/or surfaces 21, 22 to compensate for the applied forces.

An impact device 1 that is continuously controllable in terms of impact rate and impact force contains a percussion piston 25 that can move back and forth in the inner boring of the cylinder 3, and that is controlled via a rotary valve 15 having as rotary engine 16. The rotary valve 15 and the rotary engine 16 are positioned separately from the percussion piston 25, either on or in the cylinder 3, and are linked only via portings 20, 22, 24 to the pump connection 21 and the tank connection 23, or to the double-sided piston areas A1, A2, so that the valve can be used with practically any type of impact device, without requiring substantial alteration of its structural dimensions. In addition, an advantageous continuous control of impact rate and impact force with a constant power output is ensured.

The impact hammer comprises a working piston (22) exerting impacts onto an impact surface (23). The hydraulically driven working piston (22) is reciprocatingly controlled by a control means (40,41). At the rearward end of the working cylinder (21), there is a rear chamber (50) into which the projection of the piston (51) immerses. Connected to the rear chamber (50) is a pressure gas reservoir (52) which is charged with each return stroke of the working piston and discharges with the subsequent working stroke.

A hydraulically operated hammer drill includes a housing in which a striking piston is displaceably disposed for alternating movement. The striking piston is driven in striking and return directions by a first operating pressure. A rotatable, tool receiving device is connected to the housing for receiving an insertion end of a drilling tool and permitting displacement of the insertion end in the longitudinal direction when charged by the striking piston. A rotation drive mechanism, driven by a second operating pressure, is mounted for rotatably driving the tool receiving device during longitudinal displacement of the insertion end. A control unit is disposed along a pressure conduit supplying the first operating pressure for alternatingly switching the direction of movement of the striking piston by controlling application of the driving medium to control faces of the striking piston. A first control member is responsive to the second operating pressure for reducing the first operating pressure when the second operating pressure exceeds a first limit value. A second control member varies the magnitude of the expulsion pressure when a second limit value is exceeded, the second limit value being a function of the magnitude of either the first or second operating pressure.