Because of the number of variables, and the ways in which these variables are always changing, it is very tough to accurately gauge shaft seal performance on equipment in the field. As a result, sophisticated devices have been developed that allow performance variables to be closely controlled and precisely gauged in laboratory settings.

The tester shown in Figure 154 allows for the control of the test head temperature via either circulation of a heat transfer fluid or via electric heaters. In some cases, both methods are used together. Shaft speed is controlled, as is shaft-to-bore misalignment. The shaft surface is ground to specifications, and the amount of dynamic run-out can be adjusted. Seals are typically run to the point of failure (as defined and agreed on by all concerned parties prior to testing). Statistical analysis can then be used to evaluate and compare various performance capabilities. This analysis should be augmented by a detailed inspection of the seal, the test fluid, the test shaft, and the housing so that the cause of failure is completely understood.

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