Maintenance
FURNACE BLOWER ADJUSTMENT
Set adjustable motor pulley so blower will give approximately
The belt is drawn tight during shipment. Therefore both belt tension and sheave alignment must be rechecked by the installer. This is done when the furnace is placed in
service.
Improper belt tension and pulley misalignment are the major causes of furnace fan noise. It also causes failure of belts and bearings.
Sheave alignment is determined with a straight edge held across outer face of fan sheave. The face of motor sheave should be parallel to the straight edge at all points. See Figs.
Proper belt tension is more difficult to determine accurately. Too little tension will permit slippage causing belt wear. It may cause noise or squealing when the motor starts. Excessive tension increases motor load. It may cause the oil film between shaft and bearing to fail. This, in turn, causes the bearing to seize or burn out.
The proper belt tension is the minimum which will drive the blower without slippage. This varies with sheave diameter, fan size, and motor starting torque characteristics. The practical belt tension can best be determined by actual experience. When in doubt it is better to have the belt too loose rather than too tight. Belt tension can be judged by grasping the belt as shown. The belt should be deflected approximately one inch, without the motor moving, when moderate pressure is applied. See Fig. 39
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FIG. 36
FIG. 37
FIG. 38
FIG. 39
43
