When placing in position shafts that are to be connected by belts, care should be taken to separate them by a proper distance, so that the belt may be allowed to sag a little when running. No arbitrary rule can be given, as the location is the determining condition, but a general rule may be stated as follows: Where narrow belts are to run over small pulleys, a separation of 15 ft. is a good average, as the belt may then have a sag of about 2 in. For larger belts, the shafts should be placed farther apart, say 20 to 25 ft., and a sag of 3 to 4 in. will be permitted. If possible, shafts should be arranged so that the sag of the belt will increase the arc of contact with the pulley.

Fig. 141.   Oak Tanned Leather Belting.

Fig. 141. - Oak-Tanned Leather Belting.

If they are not so arranged, the sag will lower the efficiency of the belt.