Imbalance in Overhung Machinery

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An overhung machine is one where the fan or impeller lies outside of the bearings that support the shaft. Figure 1, below, shows an illustration of an overhung impeller.

Overhung Machine

Figure 1. Overhung impeller connected to a motor

Overhung machines tend to have high 1X forces because the weight is only supported from one side, i.e., it is cantilevered. This may result in higher failure rates compared to machinery running between bearings; therefore, balancing the machine is important.

When monitoring an overhung machine, take vibration readings at the bearing closest to the overhung fan or impeller. This will produce a higher amplitude signal compared to a bearing further away from the fan or impeller. Vibration signals at the bearings, for machines similar to the illustration in Figure 1, will be in phase.

Technologies such as Perpetual Industries patented XYO Balancer can be of great service in overhung machines. By automatically compensating for 1X imbalance forces in an overhung machine, XYO can reduce vibration and limit mechanical wear on the bearings and other rotating components.