Lubricating oils, particularly relatively low-viscosity oils, are much more difficult to retain than greases. Therefore, HMS5 or CRW1 spring-loaded radial shaft seals (fig 1 and fig 2) are recommended in order to achieve the necessary radial load and resistance to dynamic runout and shaft-to-bore misalignment for a satisfactory sealing performance.
Standard HMS5 seals have a straight lip while CRW1 seals are designed with SKF WAVE lips to provide improved pumping ability, regardless of the direction of shaft rotation (fig 3). Another way of increasing a seal’s pumping ability is to add a helix pattern, i.e. hydrodynamic features, to the sealing lip design.
The rubber outside diameter, like the one found on HMS5 seals, helps compensate for small imperfections in the housing bore surface and is therefore recommended when the required housing bore surface is questionable.
For very tough operating conditions, where circumferential speeds are relatively low, metal face seals, like the HDDF seal (fig 4), can be used for both oil or grease retention.
V-rings (fig 5) may also be used to retain oil, provided they are installed on the oil side and supported axially on the shaft.