Cookies on the SKF website

We use cookies to ensure that we give you the best experience on our websites and web applications. By continuing without changing your browser settings, we assume you give your consent to receive cookies. However, you can change your browser cookie setting at any time.

Types of seals

The purpose of a seal is to prevent any contaminants from entering into a controller environment. External seals must be able to prevent media from passing between a stationary and rotating surface, e.g. a housing and shaft. Integral bearing seals must be able to keep contaminants out and lubricant in the bearing cavity.
To be effective, the seal should be sufficiently capable of deformation to be able to compensate for any surface irregularities but also be strong enough to withstand operating pressures. The materials from which the seal is made should also be able to withstand a wide range of operating temperatures, and have appropriate chemical resistance.
There are several seal types; for example, DIN 3750 distinguishes between the following basic types
  • seals in contact with stationary surfaces
  • seals in contact with sliding surfaces
  • non-contact seals
  • bellows and membranes.
The seals in contact with stationary surfaces are known as static seals and their effectiveness depends on the radial or axial deformation of their cross section when installed. Gaskets (fig 1) and O-rings (fig 2) are typical examples of static seals.
Seals in contact with sliding surfaces are called dynamic seals and are used to seal passages between machine components that move relative to each other either linearly or in the circumferential direction. These dynamic seals have to retain lubricant, exclude contaminants, separate different media and withstand differential pressures. There are various types of dynamic seals, including packing and piston seal rings, which are used for linear or oscillating movements. However, the most common seal is the radial shaft seal (fig 3), which is used in a wide variety of applications in all branches of industry.
Non-contact radial shaft seals function by virtue of the sealing effect of a narrow, relatively long gap, which can be arranged axially, radially or in combination. Non-contact seals, which range from simple gap-type seals to multi-stage labyrinths (fig 3) are practically without friction and do not wear.
Bellows and membranes are used to seal components that have limited movement relative to each other.
Bellows and membranes are used to seal components that have limited movement relative to each other.
Because of the importance of dynamic radial seals for the efficient sealing of bearing arrangements, the following information deals almost exclusively with radial seals, their various designs and executions.
SKF logo