Abstract: A vibratory power screen normally has a generally planar and longitudinally extending frame having upstream and downstream ends and a pair of laterally spaced side members extending longitudinally between the ends. A generally planar screen is spanned longitudinally within the frame normally between its ends. The entire frame is tilted down from the upstream to the downstream end. Thus when particulate material is loaded onto the screen at the upstream end the particulate material migrates down along the screen to the downstream end with the smaller fractions falling through the screen. This sieve has respective pivot plates rotatably supporting beater shafts on the side members of the frame for rotation about respective substantially parallel adjustment axes extending transversely of the frame underneath the screen. Beater arms, which extend parallel to the screen from the beater shafts, have outer ends which engage the underside of the screen.