Abstract: The stock slurry pulsing rotary foils in a cylindrical paper making machine screen comprise sets which are shorter than the screen and respectively extend from opposite ends of the screen and have their inner end portions alternating in circumferentially spaced but axially overlapping relation. Thereby, the frequency of the hydraulic pulses transmitted directly to the accepts outlet is increased, but the total amplitude of the foil pulses transmitted to the outlet pipe is reduced, and this is accomplished without significant change in horsepower for driving the foil means, as compared with an arrangement of half the total number of foils wherein each foil extends throughout the effective length of the screen.