A plunger-type jig with the plunger beneath the screen. May be either single or multiple compartments. Its distinguishing features are (1) the stroke is produced with a cam operated by a lever and rocker-arm mechanism, (2) the weight of the column of water 1671 above the plunger is balanced by means of compressed air, (3) automatic operation is obtained by means of a submerged float that measures the specific gravity of the mass of coal, refuse, and water at the peak of the pulsion stroke, (4) refuse is withdrawn through a star gate extending the full width of the overflow lip, and (5) the slope of the screen plate is readily adjustable by means of heavy screws at the feed end. It is widely used on bituminous coal on sizes ranging up to a maximum of 6 in (15 cm).