Abstract: The invention concerns a drilling apparatus for enlarging a bore in the ground, comprising a drilling head (6) having a drilling bit (12); a percussion piston (14) which is driven by a drive medium (9) and which impacts against the drilling bit (12), and a hollow drill string (8) to which the drilling head (6) is fixed and through the cavity of which the drive medium (9) is passed to the percussion piston (14). The drill string (8) is surrounded by a hollow outer string (3) enclosing an annular space which surrounds the drill string (8) and through which the drive medium (9) is passed out of the borehole. The invention further concerns a method of enlarging an existing borehole, using a drilling head of that kind.

Abstract: The ground-drilling device comprises an elongated mount (10) comprising a track (11) for guiding a main carriage (25). The drive means for the main carriage (25) consists of a piston-cylinder unit (27) which extends below the track (11) under the main carriage and whose cylinder (28) is supported on the mount (10) via a link (29). The piston rod (30) engages the fore end of the main carriage (25). The piston-cylinder unit (27) does not project or only slightly projects beyond the rearward end of the mount (10).

Abstract: A pneumatic hammer is provided which includes a working piston (16) movable in a working cylinder (22) and defining therewith front and rear cylinder working chambers (23, 24, respectively). The working piston (16) impacts upon an anvil (15) to drive a drill bit (12) through utilizing a source of compressed air. An adjusting mechanism (37) adjusts the length of the return stroke of the working piston (16) in dependence upon the supply pressure of the compressed air.

Abstract: A pneumatic hammer is provided with an adjusting piston (37) dependent on the supply pressure, which adjusts the stroke length of the working piston (16). Thereby, the same pneumatic hammer may be operated both at low and high supply pressures. With high supply pressures, either the early ending of the acceleration phase or the early start of the compression phase or the shortening of the working cylinder shortens the stroke length. Thereby, the pneumatic hammer performs impacts with a substantially constant single-impact energy, regardless of the supply pressure. High supply pressures increase the impact frequency. This results in a considerably improved efficiency at a high drill capacity, a reduced wear and a reduced risk of ruptures of the components of the hammer.

Abstract: Mounted on a vehicle (10), the mast (20) of a boring rig is supported by an erection hinge (18). The erection hinge (18) is provided on a first carriage (19) having a support cylinder attached (28) to it for the purpose of support and erection of the mast (20). The hydraulic erection cylinder (24), attached to the vehicle (10), is connected to the second carriage (21). The mast (20) is extended to an oblique angle by the hydraulic erection cylinder (24). The final phase of the erection of the mast (20) is completed by the retraction of the secondary take-in cylinder (27), which connects the two carriages together. When in a horizontal position, the mast (20) can be guided in a longitudinal direction in order to have a more favorable position of the center of gravity on the vehicle (10).

Abstract: A hydraulic base-load motor (M1) drives a load with the working pressure generated at the motor rising with the load. When the working pressure reaches an upper limit pressure, a hydraulic stand-by motor (M2) is switched on. Since the pressure drops upon switching on the stand-by motor, the control device is designed such that, upon reaching a lower limit pressure, it deactivates the stand-by motor again, the lower limit pressure being less than half the upper limit pressure. This switching hysteresis prevents a repeated switching over of the stand-by motor.