Abstract: In percussion drilling such as earth drilling, a hammer piston driven by pressure medium is axially reciprocally movable in a drill body to transfer impact energy to a drill shank connectable to a drill bit. The axial position of the drill shank in the drill body is monitored, and the impact energy of the hammer piston is varied as a function of said position. For this purpose a sensor in the drill body produces a signal corresponding to the axial position of the drill shank in the drill body. By means of a control valve, the signal is used to control the pressure of the pressure medium actuating the hammer piston, thereby varying the impact energy.

Abstract: A method and a device for swivelling a spray nozzle, especially for spraying concrete, over a sector between two turning positions. The speed of the swivelling movement is kept constant, regardless of the nozzle attitude. By overriding an automatic swivel control unit, the turning positions can be replaced, and once the override ceases, automatic swivelling resumes between the new turning positions.

Abstract: An apparatus for piped conveyance of material. The material to be conveyed is introduced into a conveyor pipe where it is caused to pass through a blocking section located upstream of a location where compressed air is introduced into the conveyor pipe. In the blocking section, which has an increasing through-flow area in the conveying direction, a material plug is formed by the action of compressed air introduced at the downstream end thereof. The plug seals in a direction upstream and is at its downstream end continuously broken up and blown downstream by means of compressed air.