Abstract: A liquid jet cannon having a reciprocably movable piston device (6). The piston device is held in cocked position against the action of a gas pressure accumulator (19) by liquid pressure in a first chamber (15) until initiation of a power stroke. The power stroke is initiated by depressurization of a control chamber (16), whereby a valve (11) is moved to its open position so that a flow communication (39) is created between the first chamber (15) and a second chamber (17). The first chamber is thus rapidly depressurized so that the pressure in the gas pressure accumulator (19) drives the piston device (6) into a liquid chamber (14) to produce a liquid jet pulse for breakage of the hard material.

Abstract: A hard compact material such as rock is broken by directing a high velocity jet of relatively incompressible fluid, such as water, into a hole which is drilled in the material to be broken. The jet is generated by a nozzle in alignment with the hole and is suddenly arrested in the hole in appropriate position with respect to adjacent free surfaces of the material. A jet stagnation pressure is created in the hole of sufficient magnitude and duration or jet repetion rate to break the material towards the free surfaces. Preferably, a secondary nozzle emits fluid for filling partially or wholly the hole prior to generating the high velocity jet by a primary nozzle.

Abstract: A hard compact material, such as rock, is broken by delivering a hydraulic fluid, such as water, into at least one hole which has been pre-drilled in the material to be broken, the hole functioning as an hydraulic fluid cylinder. A piston is driven into the hole to impact the fluid to generate a high pressure in the fluid and to cause tensile stress cracks in the material by the established pressure. Due to the concentration of the stress at the bottom of the hole, the cracks are initiated and spread generally radially outwardly substantially normal to the principal stress direction. A plurality of said holes may be drilled and the cracks linked together by appropriate choice of form, depth, orientation, spacing and number of the holes. Preferably, the piston is driven into the hole by means of a gun at speeds ranging up to several hundred meters per second.