Abstract: A method of erosive cutting of a hard material such as rock utilizes two spaced clusters of jets for high-pressure discharge of fluid in the course of their movement along the same longitudinal path over the hard material. One of the jet clusters has a fixed orientation for multiple-jet discharge at the hard material, while the other cluster of jets is subjected to oscillating excursions transverse to the direction of the path that both clusters are caused to follow. A cooling medium is directed at the working site between the two clusters. The result is a faster working rate and a more cleanly defined groove in the hard material, along the path of movement.

Abstract: In order to increase the delivery pressure of the reciprocating pump-actuating mechanism of hydraulic feed pumps having a high pumping capacity, stacks of thin spacer discs are provided on either side of a sealing ring sealingly engaged in a sealing position between the plunger and the cylindrical bushing, said stacks of spacer discs being axially movable along the plunger in the normal non-sealing position. A pressure-distributing bushing is disposed between the stack of spacer discs which faces the free end face of the plunger and the sealing ring, said pressure-distributing bushing rapidly compensating the pressure between said stack of spacer discs and the end face of the pressure-distributing bushing facing the sealing ring.

Abstract: To cut, bore or similarly machine rock, ore, stratified coal or other objects, a medium is delivered under high pressure through a supply pipe to a nozzle. The supply pipe is designed as a pendulum-type pipe, in particular in the form of a flexible high-pressure hose, and executes, together with the nozzle, rapid, for example oscillating and/or circular, movements along a guide. In this way, straight cuts and/or holes can be made very rapidly and simple in rock. The cut width can be controlled by the arrangement and fitting in particular of a plurality of nozzles, depending on the rock and pressure medium. In particular, an eccentric element which functions as a drive mechanism permits a circular movement of the nozzle.