XIV
A NEW SCHEME IN ROPE
TRANSMISSION[10]
The use of manila rope for transmitting power is becoming so common as to attract no comment, and it possesses so many advantages in its own field over any other method of conveying power that some objections really existing are overlooked. When a rope drive is installed according to modern practice, it is generally so successful and furnishes such an agreeable and smooth running drive that any possible objection is silenced by the many good qualities it evidently has. But, as a matter of fact, the American continuous method of installing a rope drive has a few serious drawbacks.
[10] Contributed to Power by Geo. F. Willis.
Were it possible to install a drive of say thirty ropes in such a manner that each one of the ropes had exactly the same strain on it that each other rope had, and this under varying conditions of speed and load, it is evident that the thirty ropes would work exactly as a belt of proper width to carry the load would, that the ropes would be running with exactly the same tension clear across the width of the drive, like the belt. But according to the best authorities on rope transmission, this ideal condition is impossible to obtain.
It is given as desirable, by writers on rope transmission problems, to use a take-up sheave for every twelve ropes, while ten is considered even better. The best results have been secured by using a take-up sheave for not more than eight ropes. But in any case the evil of differential driving still exists.
In truth, the only drive in which perfect conditions can exist, according to present practice, is one using but a single rope.
It is evident that when the load comes on the ropes, the entire number of ropes in use are only able to ultimately reach the same tension from the elasticity of the ropes themselves, as slipping in the grooves rarely occurs. But there is a continued and uneven strain on the ropes until the load becomes divided between them, and where ropes are used to drive a varying load, this strain must and does reduce the life of the ropes materially.