Sealing surfaces are the workpiece surfaces against which a sealing element rests in its installation position. The decisive factor for the sealing effect is that the sealing element closes the gap between the two surfaces.
Each seal has at least two sealing surfaces. This can be explained using the example of a rod seal.
A groove in the outer part (cylinder) accommodates the sealing element, while the inner part (piston) is pushed in. The primary sealing effect occurs between the two sealing surfaces on the groove base of the outer part and the surface of the inner part.
The flanks of the installation groove can be regarded as additional sealing surfaces.