Rule

Divide the power in pounds transmitted to the periphery of the pulley by the velocity of the surface of the drum.

Example

A cast-iron pulley, 4 feet in diameter, driven by a power of four horses, makes 100 revolutions per minute; what is the stress upon the belt?

33,000 X 4 = 132,000 lbs. 1 foot per minute.

4 X 3.1416 X 100 = 1256.64 feet velocity.

132000 Then ----------- = 105 lbs. - difference of the strut upon the belt and 1256.64 the resistance of the under side of it, S / C-1 = S, and S + s = P. P representing the stress transmitted by a belt, s the resistance of its under side, and P the sum of S + s, or the stress and resistance.

Illustration

What should be the resistance of the under side of a leather belt running over the semi-circumference of a cast-iron pulley, 1 foot in diameter, driven by a power of 200 lbs.!

200 / 2.4–1= 14285 lbs.