Non-contact seals, which are characterised by a final distance between sealing surfaces, in which the working medium (against which it is to be sealed) is located. The geometry of the sealing gap (size of the gap, length) and the pressure difference and the physical values of the working medium determine the sealing performance.
Given these framework conditions, sealing gaps can never be completely tight. On the other hand, it is beneficial that, as non-contact seals, they cause extremely low friction and are also non-wearing – when using clean oil.
In hydraulics, the axial gaps are predominant. In piston pumps, radial gaps also occur.