Abstract: A device intended for building up high pulse liquid pressures may find suitable application in the mining industry and can be advantageously used in constructions of hydro-power installations. The device comprises a cylinder accommodating a two-step piston having an accelerating actuator. The piston step of smaller diameter is positioned, during the piston stroke, within a high-pressure chamber communicating with a liquid supply source and fitted with an opening for the liquid discharge. The piston step of smaller diameter is provided with a rod having a widening at the free end thereof, while the high-pressure chamber has a constricted portion passing into a widening towards the opening for the liquid discharge. At the initial stage of the piston stroke, the widening of the rod overlaps the constricted portion of the chamber to lock the liquid within the chamber between the constricted portion thereof and the piston step of smaller diameter, whereby high pressure of the particular liquid is built up.