TM 5-3895-374-24-2the new conveyor has been installed and trained to run under a no load situation. The belt will, however, likely have to bere-trained under actual loaded conditions. Use the procedure which follows to train the belt properly. The following causesof common belt performance are considered axiomatic.When all portions of a belt run off through a part of the conveyor length, the cause is probably in the alignment or levellingof the conveyor structures, idlers, or pulleys in that region.If one or more portions of the belt run off at all points along the conveyor, the cause is more likely in the belt itself, in thejoints of the belt, or in the loading of the belt. When the belt is loaded off-center, the center of gravity of the load tends tofind the center of the troughing idlers, thus leading the belt off on its lightly loaded edge (see figure 3-54).These basic rules can be used to diagnose belt running ills. Combinations of these rules sometimes produce cases thatdo not appear clear-cut as to cause, but if there is a sufficient number of belt revolutions the running pattern will becomeclear and the cause disclosed. The usual cases when a running pattern does not emerge are those of erratic running,which may be found with an unloaded belt that does not trough well, or a loaded belt that is not receiving its load uniformlycentered.A.FACTORS AFFECTING TRAINING OF A BELT1.PULLEYS AND SNUBSAll pulleys should be level and should have their axis at 90° to the intended path of the belt. They should be keptthat way and not shifted as a means of training, except that snub pulleys can have their axis shifted when othermeans of training have provided insufficient correction. Pulleys with their axis at other than 90' to the belt path willlead the belt in the direction of the edge of the belt that first contacts the misaligned pulley. When pulleys are notlevel, the belt tends to run to the low side. This is contrary to the old rule-of-thumb statement that a belt runs tothe high side of the pulley. When combinations of these two occur, the one having the stronger influence willbecome evident in the belt performance.2. CARRYING IDLERSThe belt can be trained with the troughing idlers in two ways. Shifting the idler axis with respect to the path of thebelt, commonly known as "knocking idlers," is effective where the entire belt runs to one side along some portionof the conveyor. The belt can be centered by knocking ahead (in the direction of belt travel) the end of the idler towhich the belt runs. Slots are provided on the troughing idler brackets. Shifting idlers in this way should be spreadover some length of the conveyor preceding the region of the trouble. It will be recognized that a belt might bemade to run straight with half the idlers knocked one way andpage 3 - 1254
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