There is provided method and apparatus for creating a longitudinally disposed, sharp pulse of liquid, useful for pulseback renewal of liquid-entry faces of a panel-bed liquid filter or a panel-bed liquid-powder contactor. Perforations are disposed along the wall of a tank in a path generally parallel to the tank's axis. Stoppers are provided for stoppering the perforations. With the perforations so stoppered, a liquid is introduced at high pressure into the tank. Thereafter, a quick unstoppering of the perforations releases the liquid from the tank in form of a longitudinally disposed, sharp pulse of liquid moving in a direction perpendicular to the tank's axis. If the tank is placed vertically alongside or within a space that in normal operation receives liquid from a panel bed, the sharp pulse can effectively pulseback the panel bed.