Seal Tolerance Charts

It is almost impossible, in practice, to manufacture seal components with absolute dimensional accuracy; actual production parts may vary slightly from dimensional drawings. Given this fact, it becomes necessary that the nominal dimensions of critical contact points fall within certain acceptable ranges or tolerances to allow for reliable operation. These tolerances for nominal diameters are published by the Rubber Manufacturers Association and are used by most major seal manufacturers. The tolerances recognize for instance, one critical point of contact in a shaft seal as the point between the seal OD and the housing bore. Shaft seals are typically press fit into a housing bore and to ensure a snug fit, the seal OD is produced larger than the housing bore. Typically, metal OD seals are .004" to .008" larger than the bore and rubber-covered OD's .006" to .012" larger than the bore depending on the bore size. Rubber-covered OD's are larger because the rubber OD needs to generate sufficient interference or sealing force between the OD and bore to prevent leakage and "creep" or movement of the seal within the bore. When designing or installing a shaft seal, the bore and seal OD tolerances should be considered to ensure proper equipment operation and reduce down time. The following table represents the recommended tolerances between bore and seal OD for a bore made from ferrous materials* operating under normal conditions.