Abstract: Discrete volumes, or slugs, of liquid are accelerated to high velocities utilizing energy stored by compressing the liquid. Liquid is forced into a pressure vessel already filled with liquid to effect the compression. A slug of liquid is ejected from the pressure vessel into a cumulation nozzle by the energy stored in the compressed liquid when a valve is rapidly opened. The valve is unseated when an unseating force exceeds a closing bias. The valve is then opened rapidly by an opening force generated by the compressed liquid. By repetitively introducing highly pressurized liquid into the pressure vessel, the valve automatically cycles to generate a series of pulsed liquid jets. Rapid opening of the valve is aided by an extension on the valve member which sealingly slides inside the passage of the cumulation nozzle to block release of liquid until the valve member accelerates sufficiently that the required opening rate is achieved as the extension clears the nozzle passage.