Abstract: There is described a device for purifying liquids, with a grate, a toothed beam movable opposite thereto, and means to move said teeth in an endless path relative to said grate with a rising run and a falling run, in such a way that at the start of said falling run, said teeth perform a backward swinging to an unoperative position, and during the transition between the falling run and rising run, said teeth perform a further swinging in the same direction to a position wherein said teeth project anew through said grate.