Good shaft seal design must also take into account any and all shaft eccentricity. Eccentricity may manifest itself as shaft-to-bore misalignment (STBM) and/or dynamic run-out (DRO). As shown in Figure 134, shaft-to-bore misalignment is the amount (expressed as a Total Indicator Reading, TIR, in inches or millimeters) that the shaft center is offset relative to the bore center. A static measurement taken with the shaft at rest, STBM almost always exists to some degree but should never be more than 0.010 in (0.25 mm) TIR.

As Figure 135 shows, dynamic run-out is the amount (expressed as a TIR in inches or millimeters) that the shaft’s sealing surface does not rotate around the true center. A dynamic measurement taken by applying an indicator to the side of the shaft as it slowly rotates, DRO should never exceed 0.010 in (0.25 mm) TIR. As shown in Table 43, seal life decreases as DRO increases. Table 44 lists the maximum eccentricity values (STBM plus DRO) in both inches and millimeters for most common seals.

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