Oil seals: Coaxiality and Eccentricity

Oil seals: Coaxiality and eccentricity

Coaxiality

The centerlines of the shaft and housing bore should be as closely matched as possible. Otherwise the deviation between both would lead to an improperly positioned sealing lip and force being unevenly distributed across it. This deviation should be kept within certain limits. If not, this would lead to one section of the sealing lip being subjected to more force (thus enlarging the contact area between lip and counterface), while tension over the opposite section will decrease (thus reducing its sealing effect). Sections exposed to more friction will suffer higher rates of wear, thus shorter duration of life and malfunction (leakages).

Eccentricity/Runout

Runout describes the dynamic eccentricity of the shaft. If the sealing lip is not being able to follow the shaft counterface, and this discrepancy is large enough to create a gap between seal and shaft, the medium to be sealed may escape through this gap. This is especially likely to happen at higher rotational speeds. It is advisable to avoid dynamic eccentricity, although minimal deviations would be compensated for by the elasticity of the sealing lip.