Figs. 2,804 and 2,805.—A good method of lacing a belt. The view at the left shows outer side of belt, and at the right, inner or pulley side.
Example.—If a steam engine, running 300 revolutions per minute, have a belt wheel 48 inches in diameter, and be belted to a dynamo having a pulley 12 inches in diameter, how many revolutions per minute will the dynamo make?
The speed of dynamo will be 300 × (48 ÷ 12) = 1,200 rev. per min.
Rule.—When the speed of the driving pulley and its diameter are known, and the diameter of the driven pulley is known, the speed of the driven pulley is found by multiplying the speed of the driver by its diameter in inches and dividing the product by the diameter of the driven pulley.
Example.—What will be the required speed of an engine having a belt wheel 46 inches in diameter to run a dynamo 1,500 revolutions per minute, the dynamo pulley being 11 inches in diameter?
The speed of the engine is 1,500 × (11 ÷ 46) = 359 rev. per min. nearly.
