In practice, there is little or no differential pressure. When the rotary shaft seal is exposed to pressure, the sealing lip is pressed against the shaft, thereby increasing the temperature. In some cases, the pressure may cause overturning of the sealing lip.
At higher peripheral speed and pressure above 0.2 bars, or at a lower peripheral speed and pressure of 0.5 bars, spare rings or specially designed rotary shaft seals with a stronger sealing lip and supporting metal insert must be used. For lower speeds, we recommend our PP types. However, permissible overpressure with PP-type shaft seals is limited (see diagram).
On request, we can provide shaft seals with special reinforced lip to withstand pressure over the indicated value. If spare rings are installed, standard shaft seals may also be used. However, spare rings increase the cost, and often the space required for their installation is not available. Sometimes the use of spare rings is not even possible since it requires a very precise fitting as well as very low shaft eccentricity