Experimental froth height measurements have been obtained on nine dual flow trays in a 150 mm diameter glass column. The froth heights can be predicted from Azbel theory, given the height of clear liquid. A comparison of predicted and experimental froth heights at the boiling point temperature in the water-steam system showed constant clear liquid height over a restricted vapor velocity range. Froth heights observed when distilling a ternary azeotropic mixture of ethyl acetate-ethanol-water showed considerable scatter for nine dualflow trays over an F number range from 0.5 to 2.0. The minimum capacity on dualflow trays was observed at an F number of 0.75 for the water-steam system. Turndown ratios, covering a given range of froth heights, were high for the ternary system at 3.60. New economic conditions in the competitive global environment require a reexamination of dualflow trays for low cost, low tray spacing, and good turndown ratios.