Sedimentation apparatus having an improved skimming mechanism

An improved rotary sedimentation apparatus of the type including a cylindrical tank having a bottom wall, at least one rake arm structure adapted to push thickened mixture inwardly toward the center of the bottom wall, a drive and lift unit that is located at the center of the tank and that is connected to the rake arm for rotating the rake arm about the center of the tank and for selectively raising the rake arm, wherein the improvement comprises:

• an inner skimmer blade, an outer skimmer blade, a support structure vertically affixed to the rake arm, means for slideably mounting the inner blade in a radial orientation relative to the tank and for vertically sliding movement upon the support structure, said drive and lift unit including a portion which is adapted to rotate with the rake arm but which does not change its elevation when the rake arm is lifted or lowered, a cable connected between said inner blade and said last mentioned part, said cable having a length adapted to suspend the inner blade at the surface level of the liquid in the clarifier, means for pivotally mounting the outer blade to the inner blade to permit the outer blade to swing about an axis that extends radially of the tank, and scum collecting means that cooperates with the outer blade to collect scum urged forwardly ahead of the outer blade.