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Page 400 | Volume 2 | Chapter 24 | Selection and Installation

Ques. Give a rule for determining the proper size of belt.

Ans. A single belt travelling 1,000 feet per minute will transmit one horse power per inch of width; a double belt will transmit twice this amount.

EXAMPLE.—What size of double belt is required to transmit 50 horse power at 4,000 ft. speed, and what diameter pulley must be used for 954 revolutions per minute at 4,000 ft. speed of belt?
Fig. 447. - Wrong way to run a belt.
Fig. 447.—Wrong way to run a belt. The pull should not come on the top side, because, with s1ack at bottom there is a tendency to slip.
The horse power transmitted per inch is
4000/1000 x 2 = 8

accordingly, the width of belt required to transmit 50 horse power is
50 ÷ 8 = 6.25, say 6".
For 4,000 ft. per minute belt speed, the distance in inches travelled by the belt per revolution of the pulley,
4,000 x 12 / 954 = 50.31 inches
This is equal to the circumference of the pulley, and the corresponding diameter is
50.31 / π = 16.1, say 16 inches.


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