The figures describe the air taps B and E. They consist each of a wheel with six compartments fitting as nearly air-tight as possible into a frame, which is cast in one piece with the grain inlet. The same frame also carries a small countershaft with a pinion which is geared into a large wheel, which in its turn revolves the main portion of the trap slowly. The wheel, with its six compartments, is 16 in. diameter, and 8 in. wide inside.