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BELTS. 329
Length of Belts.
Small belts, such as 4 inches wide or less, will work well
when the distance between the shafts is from 12 to 15 feet, larger
belts when from 20 to 25 feet, and for large main belts 25 to 30
feet distance is satisfactory.
Horse=Power Transmitted by Belting.
A single belt weighing about 15 ounces per square foot is
capable of transmitting one horse-power per inch of width,
when running at a speed of 800 feet per minute over pulleys of
proper size, both of equal diameter. As one horse-power is
33,000 foot-pounds of work per minute, this will make the tension
, , , , • • • 33000
due to the power the belt is transmitting = 8QQ
= 41 >< lbs.
per inch of width, but the total tension in the belt is, of course,
considerably more per inch of width, because the belt must be
tight enough to prevent its slipping on the pulley. For belts
lighter than 15 ounces per square foot it is better to allow 1000
running feet per horse-power per inch of width of belt. For light
double belts weighing 21 ounces per square foot, 600 running
feet per horse-power per inch of width may be allowed. For
double belts weighing 25 ounces per square foot, 500 running
feet per horse-power per inch of width may be allowed. Hence
the following formulas :
For light single belts weighing less than 15 ounces per
square foot,
H — _^-X— a - //X 10(j0 •
1000
b ~ v
For single belts weighing 15 to 16 ounces per square foot,
rr V X b H X 800
tl = h —
800 ° ~ v
For light double belts weighing about 21 ounces per square
foot,
v X b . H X 600
H -
600 v
For double belts weighing about 25 ounces per square foot,
_ * X_?_
b - HX 50°
H ~ 500 v
H = Horse-power.
b = Width of belt in inches.
v = Velocity of belt in feet per minute, which will be di-
ameter of pulley in inches multiplied by 3.1416 and by the num-
ber of revolutions per minute, and the product divided by 12.
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