SAF and SAW pillow (plummer) block housings are available with different standard sealing solutions.
Table 1 provides an overview of the characteristics and suitability of each sealing solution. Details are provided in the following text. This information should be used as a guideline, which cannot substitute for testing a seal in its application. Table 2 provides an overview about which seals fit what housing.
Labyrinth seals are the standard sealing solution for SAF and SAW housings. They are available in two variants depending on housing size:
- Labyrinth seals with the designation LER (fig. 1), also called triple ring seals, are supplied standard with small SAF housings (shaft diameter ≤ 2 5/8 inch). The rings form a multi-stage labyrinth seal with the housing seal grooves. If operating conditions warrant it, the sealing effect can be enhanced by filling the cavity between the housing and seal ring with grease.
- PosiTrac labyrinth seals, designation LOR (fig. 2), are supplied standard with larger SAF (shaft diameter ≥ 2 1/8 inch) and all SAW housings. These seals have an additional O-ring made of acrylonitrile-butadiene rubber (NBR) to make the labyrinth ring rotate with the shaft.
Labyrinth rings with an internal contact element
PosiTrac Plus seals (fig. 3) consist of a PosiTrac labyrinth ring (designation LOR) and a contact element made of acrylonitrile-butadiene rubber (NBR). The labyrinth ring is located on the shaft and held in place by an O-ring.
The contact element is located in the seal groove in the housing. It can be mounted either for best contaminant exclusion (fig. 4) or for best lubricant retention (fig. 5). When the contact element is mounted for best contaminant exclusion, the sealing effect can be enhanced by filling the seal cavity with grease. The designation for the contact element is B 10724 followed by a size code, for example B 10724-122.
Taconite heavy-duty seals
To further protect against the ingress of contaminants, SKF taconite seals have a grease fitting to purge grease and any trapped contaminants from the seal cavity, through the outboard seal.
Contact seals (fig. 8) are solid seals that fit into the seal groove. Contact seals are available for smaller housing sizes (SAF 513 and smaller) where PosiTrac Plus seals are not available. The designation for contact seals is B 9784 followed by a size code, e.g. B 9784-15.
Housings at the end of a shaft should have an end plug (end cover) (fig. 9) that fits into the seal groove in the housing. The plug consists of a metal plate with a strip made of acrylonitrilebutadiene rubber (NBR). Details of the permissible length of the shaft end are listed in the product tables for:
End plugs are identified by the designation EPR, followed by a size code, for example EPR 7.