In the diagram given below, the curve A refers to single belts, best oak tanned, curve B to similar light double belts, and the remaining curve C to heavy double belts. Each curve shows the horse-power that may be transmitted by a belt for each inch in width. Thus a single belt l in. wide will transmit about 3 horse-power when running at a speed of 2,000ft. per minute. Similarly, at that speed, a light double belt will transmit rather more than 4.2 horse-power per inch of width, while a heavy double belt would transmit about 5.4 horse-power. It will be noticed that the lines curve upward at the higher speeds, the decreased power thus shown being accounted for by the centrifugal force set up. To keep the belt central with the face of the pulley, the latter should be slightly rounded, say 3/8 in. or 1/2 in. per foot.

Power Transmitted by Leather Belts.