Shaft seals (WDR) are seals that are used to provide sufficient protection, e.g. for machine housings, shafts or push rods. The most common shaft seals and their designs are standardised in Germany in the DIN standard DIN 3760.
Radial oil seals (RWDR) are installed with a tight fit in the housing or housing cover. Their sealing lip runs on the surface of the rotating shaft and is usually pressed radially onto the surface of the shaft by a tubular spring (worm spring). In order to reduce wear on the rubber lip and to ensure the sealing effect, high demands are placed on the quality of the shaft surface; For this reason, the shaft is often ground free in the area of the sealing tread. Newer designs of the RWDR sometimes no longer have a worm spring (diaphragm shaft seals) or have a PTFE sealing lip.
Contrary to its original purpose, RWDR is also used as a fork seal ring on motorcycles to prevent oil and air from escaping between the standpipes and immersion tubes, thus ensuring the function of the damper integrated in the fork. When springing in and out, the seals move axially over the (usually chrome-plated and polished) immersion tubes.
In case of pressure differences between the areas separated by the seal, the open side of the seal ring should face the higher pressure area. The sealing lip is then pressed against the shaft by the pressure difference. In the reversed case, the sealing lip can be pushed away from the shaft against the spring force. The sealing effect is then lost.
