Ques. Under what conditions does a belt drive give the best results?
Ans. When the two pulleys are at the same level.
If the belt must occupy an inclined position it should not form a greater angle than 45 degrees with the horizontal.
Ques. What is a characteristic feature in the operation of belts, and why?
Ans. Belts in motion will always run to the highest side of a pulley; this is due partially to the greater speed in feet per minute developed at that point owing to the greater circumference of the pulley, and also to the effects of centrifugal force.
If, therefore, the highest sides of both pulleys be in line with each other, and the shafts of the respective pulleys be parallel to each other, there will be no tendency for the belt to leave the pulleys when once in its proper position. In order that these conditions be maintained, the belt should be no more than tight enough to prevent slipping, and the distance between the centers of the pulleys should be approximately 3.5 times the diameter of the larger one.
Fig. 2,818.—Hill clutch mechanism Smith type. The friction surfaces are wood to iron, the wood shoes being made from maple. All parts of the toggle gear are of steel and forgings with the exception of the connection lever which is of cast iron.
Ques. What minor appurtenances should be provided in a station?