XIII
ROPE DRIVES[9]
There seems to be considerable difference in opinion regarding the various ways of applying rope to the sheaves in rope driving, viz., multiple- or separate-rope system, continuous-wrap or single-rope system with the rope from one of the grooves running on a traveling take-up device, continuous-wrap or single-rope system with the take-up working directly on all the wraps.
[9] Contributed to Power by R. Hoyt.
Fig. 85.
The multiple- or separate-rope system on a horizontal drive where the distance between centers is great enough so that the weight of the rope will give the required tension, having the tight or pulling part on the lower side and the sheaves of the same diameter, as in Fig. 85, should be very satisfactory, as old or worn ropes may be replaced by new ones of larger diameter, or some of the ropes may be tighter than others and still not alter the efficiency of the drive. It will be noticed in this case that a larger rope does not alter the proportional pitch diameters of the rope on the driving and driven sheaves; but if one of the sheaves is larger than the other, as in Figs. 86 and 87, and a new or larger rope is substituted for a worn or smaller one, or if some of the ropes are a great deal tighter than others, a differential action will be produced on the ropes owing to the fact that the larger or slack rope will not go as deeply into its grooves as the smaller or tight one. Consequently the proportionate pitch diameter on the rope on the driver and driven sheave will be changed. The action will depend upon whether the large or the small sheave is the driver. If the driver is the larger, and of course assuming that the slack or large rope is weaker than the combined tight or smaller ones, then it will have less strain on the pulling side; but if the driver is smaller, then the new or large rope will have greater strain on the pulling side. Whether the driver is larger or smaller, a large or slack rope affects the action oppositely to a small or tight rope. Fig. 87 shows how the action is reversed from Fig. 86.
Fig. 86.
