Both winches A and B, shown in the left illustration, can be turned either in the same or in opposite directions, this being accomplished by the use of a pairof wheels, of friction clutches, and of a third wheel c, which can be coupled between the two larger spur wheels. If both drums revolve in the same direction, they both wind up Both winches A and B can be turned either in the same or in opposite directions, this being accomplished by the use of a pair of wheels, of friction clutches, and of a third wheel c, which can be coupled between the two larger spur wheels. If both drums revolve in the same direction, they both wind up the rope, and thus elevate the load; whereas, in the other case, one drum winds up as much rope as the other pays out, and the load is therefore conveyed in a horizontal direction.
In a scheme such as is illustrated in the right figure, the load is supported on an endless rope which is wound round the conveying drum B, and by means of this drum can be drawn either backward or forward. The drum A is for lifting and lowering the load by shortening or lengthening the endless rope which supports it, this being accomplished by a pair of jockey pulleys, as shown in the illustration.