Rule.—Multiply the diameter of driven by its number of revolutions, and divide by the diameter of the driver.
SHAFTS AND PULLEYS.
To find the size of pulley needed to give the main shaft a certain number of revolutions, multiply the diameter of fly-wheel in inches by the number of revolutions of the engine, and divide by revolutions of main shaft.
To find the revolutions of main shaft when diameter of its pulley is given, multiply the diameter of fly-wheel in inches by its number of revolutions, and divide by the diameter of pulley in inches.
To find diameter of fly-wheel needed to drive a pulley at a given number of revolutions, multiply the diameter of pulley in inches by its number of revolutions, and divide by number of revolutions of the engine.
To find revolutions of an engine with a given fly-wheel to drive a pulley at a given number of revolutions, multiply the diameter of pulley in inches by its number of revolutions, and divide by the diameter of fly-wheel in inches.
Rule for finding the amount of heating surface in a locomotive boiler:
Find surface of flues by multiplying the diameter by 3.14 to get circumference, and multiply this product by the length of the flue, then multiply this result by the number of flues in the boiler, and divide by 144 to get number of square feet of surface in the flues.
Multiply length and width of fire box for number of square inches in crown sheet, then multiply the length and height of the fire box and the result by two, which gives the number of square inches in the sides; then multiply the width and height and multiply the result by two, which gives the number of square inches in the ends, from which subtract number of square inches in space left for door and flues—then add all these results together and divide by 144 to get the number of square feet in the fire box. Add same to number of square feet of flues, and the total will be the number of square feet in the boiler.
By dividing number of square feet by rated horse-power of boiler will give number of square feet of heating surface to each horse-power.